LM73606QURNPRQ1_技术文档

LM73605-Q1, LM73606-Q1

SNVSB12B – NOVEMBER 2017 – REVISED MAY 2021

LM7360x-Q1 3.5-V to 36-V, 5-A or 6-A Synchronous

Step-Down Voltage Converter

1 Features

3 Description

•

AEC-Q100-qualified for automotive applications

– Device temperature grade 1: –40°C to +125°C

ambient operating temperature

– Device HBM ESD classification level 2 kV

– Device CDM ESD classification level C5

Wettable flanks QFN package (WQFN)

Low EMI and low switching noise

Low quiescent current

– 0.8 µA in shutdown (typical)

– 15 µA in active mode with no load (typical)

Wide voltage conversion range:

– t_ON-MIN= 60 ns (typical)

– t_OFF-MIN= 70 ns (typical)

The LM73605-Q1/LM73606-Q1 family of devices

are easy-to-use synchronous step-down DC/DC

converters capable of driving up to 5 A (LM73605-Q1)

or 6 A (LM73606-Q1) of load current from a supply

voltage ranging from 3.5 V to 36 V. The LM73605-

Q1/LM73606-Q1 provide exceptional efficiency and

output accuracy in a very small solution size.

Peak current-mode control is employed. Additional

features such as adjustable switching frequency,

synchronization to an external clock, power-good flag,

precision enable, adjustable soft start, and tracking

provide both flexible and easy-to-use solutions for

a wide range of applications. Automatic frequency

foldback at light load and optional external bias

improve efficiency over the entire load range. The

family requires few external components and has a

pinout designed for simple PCB layout with optimal

EMI and thermal performance. Protection features

include thermal shutdown, input undervoltage lookout,

cycle-cy-cycle current limiting, and hiccup short-

citcuit protection. The LM73605-Q1 and LM73606-Q1

devices are pin-to-pin compatible for easy current

scaling.

•

Low MOSFET ON-resistance:

– R_{DS_ON_HS}= 53 mΩ (typical)

– R_{DS_ON_LS}= 31 mΩ (typical)

•

Adjustable frequency range: 350 kHz to 2.2 MHz

Pin-selectable auto mode or forced PWM mode

Start-up into pre-biased load, fixed or adjustable

soft-start time, and tracking

Synchronizable to external clock, internal

compensation, power-good flag, and precision

enable

Cycle-by-cycle current limiting, hiccup, UVLO, and

thermal shutdown protections

Create a custom design with the WEBENCH^®

power designer using LM73605-Q1 or LM73606-

Q1

•

Device Information⁽¹⁾

PART NUMBER

PACKAGE

BODY SIZE (NOM)

LM73605-Q1

WQFN (30)

Wettable and non-

wettable flanks

6.00 mm × 4.00 mm

LM73606-Q1

(1) For all available packages, see the orderable addendum at

the end of the data sheet.

2 Applications

•

Automotive distributed power applications

Battery-powered applications

General-purpose wide V_INapplications

100

95

90

85

80

75

70

65

L

V_IN

V_OUT

SW

PVIN

C_BOOT

C_OUT

C_IN

EN

CBOOT

BIAS

RT

PGND

PGOOD

SS/TRK

R_FBT

60

SYNC/

MODE

Freq = 400 kHz

Freq = 2.2 MHz

FB

55

R_FBB

50

VCC

0.001

0.01 0.02 0.05 0.1 0.2

Load Current (A)

0.5

1

2 3 45

C_VCC

AGND

EFF_

Efficiency versus Load Current V_OUT= 5 V, V_IN= 12

V, Auto Mode

Simplified Schematic

An IMPORTANT NOTICE at the end of this data sheet addresses availability, warranty, changes, use in safety-critical applications,

intellectual property matters and other important disclaimers. PRODUCTION DATA.

LM73605-Q1, LM73606-Q1

SNVSB12B – NOVEMBER 2017 – REVISED MAY 2021

www.ti.com

Table of Contents

1 Features............................................................................1

2 Applications.....................................................................1

3 Description.......................................................................1

4 Revision History.............................................................. 2

5 Device Comparison.........................................................3

6 Pin Configuration and Functions...................................4

7 Specifications.................................................................. 6

7.1 Absolute Maximum Ratings........................................ 6

7.2 ESD Ratings............................................................... 6

7.3 Recommended Operating Conditions.........................6

7.4 Thermal Information....................................................7

7.5 Electrical Characteristics.............................................7

7.6 Timing Characteristics.................................................9

7.7 Switching Characteristics............................................9

7.8 System Characteristics............................................... 9

7.9 Typical Characteristics..............................................10

8 Detailed Description......................................................12

8.1 Overview...................................................................12

8.2 Functional Block Diagram.........................................12

8.3 Feature Description...................................................13

8.4 Device Functional Modes..........................................26

9 Layout.............................................................................47

9.1 Layout Guidelines..................................................... 47

9.2 Layout Example........................................................ 50

10 Device and Documentation Support..........................51

10.1 Device Support....................................................... 51

10.2 Documentation Support.......................................... 51

10.3 Receiving Notification of Documentation Updates..51

10.4 Receiving Notification of Documentation Updates..51

10.5 Support Resources................................................. 52

10.6 Support Resources................................................. 52

10.7 Trademarks.............................................................52

10.8 Electrostatic Discharge Caution..............................52

10.9 Glossary..................................................................52

4 Revision History

Changes from Revision A (November 2018) to Revision B (May 2021)

Page

•

Updated the numbering format for tables, figures, and cross-references throughout the document. ................1

Added "and non-wettable flanks" to the Device Information table......................................................................1

Added the Device Comparison Table ................................................................................................................ 3

Changes from Revision * (November 2017) to Revision A (November 2018)

Page

•

Added wording for new product..........................................................................................................................1

2

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5 Device Comparison

Table 5-1. Device Comparison Table

DEVICE NAME

WETTABLE (WF)/NON-WETTABLE FLANKS (NON-WF)

PACKAGE

QTY⁽¹⁾

LM73605QRNPRQ1

LM73605QRNPTQ1

LM73606QRNPRQ1

LM73606QRNPTQ1

LM73605QURNPRQ1

LM73606QURNPRQ1

WF

3000

250

WF

3000

250

WF

non-WF

3000

(1) See the Package Option Addendum for tape and reel details as well as links to order parts

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6 Pin Configuration and Functions

NC

30

NC

29

NC

28

NC

27

26

25

24

23

22

PGND

PVIN

SW

1

2

3

4

5

SW

CBOOT

VCC

21

20

19

18

17

6

7

DAP

PVIN

BIAS

AGND

8

RT

9

EN

SYNC/

MODE

SS/TRK

FB

10

11

16

PGOOD

13

14

NC

15

NC

12

NC

Figure 6-1. RNP Package 30-Pin Wettable Flanks QFN (WQFN) 6 mm × 4 mm × 0.8 mm Top View

Table 6-1. Pin Functions

I/O⁽¹⁾

DESCRIPTION

NO.

NAME

Switching output of the regulator. Internally connected to source of the HS FET and drain of the LS

FET. Connect to power inductor and bootstrap capacitor.

1, 2, 3, 4, 5

SW

P

Bootstrap capacitor connection for HS FET driver. Connect a high-quality 470-nF capacitor from

this pin to the SW pin.

6

7

CBOOT

VCC

Output of internal bias supply. Used as supply to internal control circuits and drivers. Connect a

high-quality 2.2-µF capacitor from this pin to GND. TI does not recommend loading this pin by

external circuitry.

P

Optional BIAS LDO supply input. TI recommends tying to V_OUTwhen 3.3 V ≤ V_OUT≤ 18 V, or tie to

an external 3.3-V or 5-V rail if available, to improve efficiency. BIAS pin voltage must not be greater

than V_IN. Tie to ground when not in use.

8

9

BIAS

RT

P

A

Switching frequency setting pin. Place a resistor from this pin to ground to set the switching

frequency. If floating, the default switching frequency is 500 kHz. Do not short to ground.

Soft-start control pin. Leave this pin floating for a fixed internal soft-start ramp. An external

capacitor can be connected from this pin to ground to extend the soft start time. A 2-µA current

sourced from this pin charges the capacitor to provide the ramp. Connect to external ramp for

tracking. Do not short to ground.

10

11

SS/TRK

A

Feedback input for output voltage regulation. Connect a resistor divider to set the output voltage.

Never short this pin to ground during operation.

FB

I

12–15, 27–

30

No internal connection. Connect to ground net and copper to improve heat sinking and board-level

reliability.

NC

—

Open drain power-good flag output. Connect to suitable voltage supply through a current limiting

resistor. High = V_OUTregulation OK, Low = V_OUTregulation fault. PGOOD = LOW when EN = low

and V_IN> 2 V.

16

17

PGOOD

O

I

Synchronization input and mode setting pin. Do not float. Tie to ground if not used.

Tie to ground: auto mode, higher efficiency at light loads;

Tie to logic high: forced PWM, constant switching frequency over load;

Tie to external clock source: forced PWM, synchronize to the rising edge of the external clock.

SYNC/MODE

4

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Table 6-1. Pin Functions (continued)

I/O⁽¹⁾

DESCRIPTION

NO.

NAME

Enable input to regulator. Do not float. High = ON, Low = OFF. Can be tied to PVIN. Precision

enable input allows adjustable input voltage UVLO using external resistor divider.

18

EN

I

Analog ground. Ground reference for internal circuitry. All electrical parameters are measured with

respect to this pin. Connect to system ground on PCB.

19

AGND

PVIN

PGND

DAP

G

Supply input to internal bias LDO and HS FET. Connect to input supply and input bypass capacitors

C_IN. C_INmust be placed right next to this pin and PGND pins on PCB, and connected with short

and wide traces.

20–22

23–26

EP

P

G

Power ground, connected to the source of LS FET internally. Connect to system ground, DAP/EP,

AGND, ground side of C_INand C_OUTon PCB. Path to C_INmust be as short as possible

Low impedance connection to AGND. Connect to system ground on PCB. Major heat dissipation

path for the device. Must be used for heat sinking by soldering to ground copper on PCB. Thermal

vias are preferred to improve heat dissipation to other layers.

(1) A = Analog, O = Output, I = Input, G = Ground, P = Power

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7 Specifications

7.1 Absolute Maximum Ratings

Over operating free-air temperature range of –40°C to +125°C (unless otherwise noted)⁽¹⁾

PARAMETER

MIN

–0.3

–0.1

–0.3

–3.5

–0.3

–40

MAX

UNIT

PVIN to PGND

EN to AGND

42

V_IN+ 0.3

FB, RT, SS/TRK to AGND

PGOOD to AGND

SYNC to AGND

5

Input voltages

20

V

5.5

BIAS to AGND

Lower of (V_IN+ 0.3) or 20

AGND to PGND

0.3

SW to PGND

V_IN+ 0.3

SW to PGND less than 10-ns transients

CBOOT to SW

42

5

Output voltages

V

VCC to AGND

5

Junction temperature, T_J

Storage temperature, T_stg

150

°C

–65

(1) Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are stress

ratings only, which do not imply functional operation of the device at these or any other conditions beyond those indicated under

Recommended Operating Conditions. Exposure to absolute-maximum-rated conditions for extended periods may affect device

reliability.

7.2 ESD Ratings

VALUE

±2000

±750

UNIT

Human-body model (HBM), per ANSI/ESDA/JEDEC JS-001⁽¹⁾

Charged-device model (CDM), per AEC Q100-011

V

V_(ESD)

Electrostatic discharge

(1) AEC Q100-002 indicates that HBM stressing shall be in accordance with the ANSI/ESDA/JEDEC JS-001 specification

7.3 Recommended Operating Conditions

Over operating free-air temperature range of –40°C to +125°C (unless otherwise noted)⁽¹⁾

MIN

3.5

0

MAX

UNIT

PVIN to PGND

EN

36

V_IN

FB

0

4.5

Input voltages

PGOOD

0

18

V

BIAS input not used

BIAS input used

AGND to PGND

V_OUT

0

0.3

0

Lower of (V_IN+ 0.3) or 18

–0.1

1

0.1

Output voltage

Output current

95% of V_IN

V

A

I_OUT, LM73605-Q1

I_OUT, LM73606-Q1

0

5

6

0

(1) Recommended operating rating indicate conditions for which the device is intended to be functional, but do not ensure specific

performance limits. For ensured specifications, see Section 7.5

6

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7.4 Thermal Information

LM73605/LM73606

THERMAL METRIC⁽¹⁾

RNP (WQFN)

UNIT

30 PINS

34.3

14.6

7.3

R_θJA

Junction-to-ambient thermal resistance

Junction-to-case (top) thermal resistance

°C/W

R_θJC(top)

R_θJB

Junction-to-board thermal resistance

ψ_JT

Junction-to-top characterization parameter

Junction-to-board characterization parameter

Junction-to-case (bottom) thermal resistance

0.1

ψ_JB

7.1

R_θJC(bot)

1

(1) For more information about traditional and new thermal metrics, see the Semiconductor and IC Package Thermal Metrics application

report.

7.5 Electrical Characteristics

Limits apply over the recommended operating junction temperature (T_J) range of –40°C to +125°C, unless otherwise stated.

Minimum and maximum limits are specified through test, design or statistical correlation. Typical values represent the most

likely parametric norm at T_J= 25°C, and are provided for reference purposes only. Unless otherwise stated, V_IN= 12 V.

PARAMETER

TEST CONDITIONS

MIN

TYP

MAX

UNIT

SUPPLY VOLTAGE (PVIN PINS)

Operating input voltage

range

V_IN

3.5

36

10

12

V

Shutdown quiescent current; V_EN= 0 V

measured at VIN pin⁽¹⁾

T_J= 25℃

I_SD

0.8

0.6

µA

Operating quiescent current V_EN= 2 V, V_FB= 1.5 V, V_BIAS= 3.3 V

from V_IN(non-switching)

I_{Q_NONSW}

external

ENABLE (EN PIN)

Enable input high level for

V_CCoutput

V_{EN_VCC_H}

V_{EN_VCC_L}

V_{EN_VOUT_H}

V_ENrising

1.15

V

Enable input low level for

V_CCoutput

V_ENfalling

0.3

Enable input high level for

V_OUT

V_ENrising

1.14

1.196

1.25

200

Enable input hysteresis for

V_OUT

V_{EN_VOUT_HYS}

V_ENfalling hysteresis

–100

1.4

mV

nA

I_{LKG_EN}

Enable input leakage current V_EN= 2 V

INTERNAL LDO (VCC PIN, BIAS PIN)

PWM operation

PFM operation

V_CCrising

3.27

3.1

V

V_CC

Internal V_CCvoltage

2.96

3.14

–605

3.09

–63

3.27

3.25

V

Internal V_CCundervoltage

lockout

V_{CC_UVLO}

V_CCfalling hysteresis

V_BIASrising

mV

V

V_{BIAS_ON}

Input changeover

V_BIASfalling hysteresis

mV

Operating quiescent current

I_{BIAS_NONSW}from external V_BIAS(non-

switching)

V_EN= 2 V, V_FB= 1.5 V, V_BIAS= 3.3 V

external

21

50

µA

VOLTAGE REFERENCE (FB PIN)

V_FB

Feedback voltage

PWM mode

V_FB= 1 V

0.987

1.006

0.2

1.017

60

V

Input leakage current at FB

I_{LKG_FB}

nA

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Limits apply over the recommended operating junction temperature (T_J) range of –40°C to +125°C, unless otherwise stated.

Minimum and maximum limits are specified through test, design or statistical correlation. Typical values represent the most

likely parametric norm at T_J= 25°C, and are provided for reference purposes only. Unless otherwise stated, V_IN= 12 V.

PARAMETER

TEST CONDITIONS

MIN

TYP

MAX

UNIT

HIGH SIDE DRIVER (CBOOT PIN)

CBOOT - SW undervoltage

lockout

V_{CBOOT_UVLO}

1.6

2.2

2.7

V

CURRENT LIMITS AND HICCUP

LM73605-Q1

6

7.4

7.3

8.7

5.5

6.6

–5

8.35

9.85

6.1

Short-circuit, high-side

I_{HS_LIMIT}

A

current limit⁽²⁾

LM73606-Q1

LM73605-Q1

LM73606-Q1

LM73605-Q1

LM73606-Q1

4.79

5.8

I_{LS_LIMIT}

Low-side current limit⁽²⁾

Negative current limit

7.25

I_{NEG_LIMIT}

–6

V_HICCUP

I_{L_ZC}

Hiccup threshold on FB pin

Zero cross-current limit

0.36

1.8

0.4

0.06

0.44

2.2

V

A

SOFT START (SS/TRK PIN)

I_SSC

Soft-start charge current

2

1

µA

kΩ

Soft-start discharge

resistance

R_SSD

UVLO, TSD, OCP, or EN = 0

POWER GOOD (PGOOD PIN) and OVERVOLTAGE PROTECTION

Power-good overvoltage

threshold

V_{PGOOD_OV}

V_{PGOOD_UV}

% of FB voltage

106%

86%

110%

113%

93%

Power-good undervoltage

threshold

% of FB voltage

90%

1.2%

1.3

V_{PGOOD_HYS}Power-good hysteresis

Minimum input voltage for

V_{PGOOD_VALID}

50-µA pullup to PGOOD pin, V_EN= 0 V,

T_J= 25°C

2

V

proper PGOOD function

V_EN= 2.5V

V_EN= 0 V

40

30

100

90

R_PGOOD

Power-good ON-resistance

Ω

MOSFETS

High-side MOSFET ON-

resistance

(3)

R_{DS_ON_HS}

I_OUT= 1 A, V_BIAS= V_OUT= 3.3 V

53

31

90

55

mΩ

Low-side MOSFET ON-

resistance

R_{DS_ON_LS}

THERMAL SHUTDOWN

Thermal shutdown threshold Shutdown threshold

Recovery threshold

160

135

°C

(4)

T_SD

(1) Shutdown current includes leakage current of the switching transistors.

(2) This current limit was measured as the internal comparator trip point. Due to inherent delays in the current limit comparator and

drivers, the peak current limit measured in closed loop with faster slew rate will be larger, and valley current limit will be lower.

(3) Measured at pins

(4) Ensured by design

8

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7.6 Timing Characteristics

MIN

NOM

MAX

UNIT

CURRENT LIMITS AND HICCUP

Number of switching cycles before

hiccup is tripped

(1)

N_OC

t_OC

128

46

Cycles

ms

Overcurrent hiccup retry delay time

SOFT START (SS/TRK PIN)

t_SSInternal soft-start time

C_SS= OPEN, from EN rising edge to

PGOOD rising edge

3.5

6.3

ms

POWER GOOD (PGOOD PIN) and OVERVOLTAGE PROTECTION

t_{PGOOD_RISE}

t_{PGOOD_FALL}

PGOOD rising edge deglitch delay

PGOOD falling edge deglitch delay

80

140

200

µs

(1) Ensured by design

7.7 Switching Characteristics

PARAMETER

TEST CONDITIONS

MIN

TYP

MAX

UNIT

PWM LIMITS (SW PINS)

t_ON-MIN

t_OFF-MIN

t_ON-MAX

Minimum switch on-time

Minimum switch off-time

Maximum switch on-time

60

70

6

82

120

9

ns

µs

HS timeout in dropout

3

OSCILLATOR (RT and SYNC PINS)

f_OSCInternal oscillator frequency

R_T= Open

440

315

500

350

560

385

kHz

Minimum adjustable frequency by R_Tor

SYNC

R_T=115 kΩ, 0.1%

f_ADJ

Maximum adjustable frequency by R_Tor

SYNC

R_T= 17.4 kΩ, 0.1%

1980

0.4

2200

2420

2

kHz

V_{SYNC_HIGH}

V_{SYNC_LOW}

V_{MODE_HIGH}

Sync input high level threshold

V

Sync input low level threshold

Mode input high level threshold for FPWM

0.42

0.4

80

Mode input low level threshold for AUTO

mode

V_{MODE_LOW}

t_{SYNC_MIN}

V

Sync input minimum ON and OFF-time

ns

7.8 System Characteristics

The following specifications apply to the circuit found in typical schematic with appropriate modifications from typical bill of

materials. These parameters are not tested in production and represent typical performance only. Unless otherwise stated

the following conditions apply: T_A= 25°C, V_IN= 12 V, V_OUT= 3.3 V, f_SW= 500 kHz.

PARAMETER

TEST CONDITIONS

MIN

TYP

MAX

UNIT

Output voltage offset at no load in

auto mode

V_IN= 3.8 V to 36 V, V_SYNC= 0 V, auto mode I_OUT= 0

A

V_{FB_PFM}

V_DROP

I_{Q_SW}

2%

Minimum input to output voltage

differential to maintain specified

accuracy

V_OUT= 5 V, I_OUT= 3 A, f_SW= 2.2 MHz

0.4

V

Operating quiescent current

(switching)

V_EN= 3.3 V, I_OUT= 0 A, R_T= open, V_BIAS= V_OUT

3.3 V , R_FBT= 1 Meg

=

15

1

µA

LM73605-Q1:

V_SYNC= 0, I_OUT= 10 mA

I_{PEAK_MIN}

Minimum inductor peak current

A

LM73606-Q1:

V_SYNC= 0 V, I_OUT= 10 mA

1.3

f_SW= 500 kHz, I_OUT= 1 A

f_SW= 2.2 MHz, I_OUT= 1 A

While in frequency foldback

7

mA

Operating quiescent current from

external V_BIAS(switching)

I_{BIAS_SW}

D_MAX

t_DEAD

25

Maximum switch duty cycle

97.5%

Dead time between high-side and

low-side MOSFETs

4

ns

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7.9 Typical Characteristics

Unless otherwise specified, V_IN= 12 V. Curves represent most likely parametric norm at specified condition.

1600

1500

1400

1300

1200

1100

1000

900

75

70

65

60

55

50

45

40

35

30

25

20

VIN = 3.5 V

VIN = 12 V

VIN = 36 V

HS Switch

LS Switch

800

700

600

500

400

300

200

-40

-20

0

20

40

60

Temperature (°C)

80

100

120

-40

-20

0

20

40 60

Temperature (°C)

80

100 120 140

CHPAloRt

CHAR

Figure 7-2. Shutdown Quiescent Current

Figure 7-1. High-Side and Low-Side Switches

R_DS-ON

1.01

7.5

Temp = -40°C

Temp = 25°C

Temp = 125°C

1.009

1.008

1.007

1.006

1.005

1.004

1.003

1.002

1.001

1

7

6.5

6

HS

LS

5.5

5

3

6

9

12 15 18 21 24 27 30 33 36

VIN (V)

-40

-20

0

20

40

60

Temperature (°C)

80

100

120

CHAR

Figure 7-3. Feedback Voltage

Figure 7-4. LM73605-Q1 High-Side and Low-Side

Current Limits

2500

2250

9

8.4

7.8

7.2

6.6

6

2000

FREQ = 350 kHz

FREQ = 1 MHz

1750

FREQ = 2.2 MHz

1500

HS

LS

1250

1000

750

500

250

0

-40

-20

0

20

40

60

Temperature (°C)

80

100

120

-40

-20

0

20

40

60

Temperature (°C)

80

100

120

CHAR

Figure 7-6. Switching Frequency Set by R_T

Resistor

Figure 7-5. LM73605-Q1 High-Side and Low-Side

Current Limit

10

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550

540

530

520

510

500

490

480

470

460

1.28

1.2

1.12

1.04

0.96

0.88

0.8

VEN_VOUT Rising

VEN_VOUT Falling

VEN_VCC Rising

VEN_VCC Falling

VIN = 3.5 V

VIN = 12 V

VIN = 36 V

0.72

0.64

0.56

450

-40

-20

0

20

40 60

Temperature (°C)

80

100 120 140

-20

0

20

40

60

Temperature (°C)

80

100

120

CHAR

Figure 7-8. Enable Thresholds

Figure 7-7. Switching Frequency with RT Pin Open

Circuit

115

110

105

100

95

OV Tripping

OV Recovery

UV Recovery

UV Tripping

90

85

-40

-20

0

20

40

60

Temperature (°C)

80

100

120

CHAR

Figure 7-9. PGOOD Thresholds

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8 Detailed Description

8.1 Overview

The LM73605-Q1/6-Q1 easy-to-use synchronous step-down DC/DC converters that operate from a 3.5-V to

36-V supply voltage. It is capable of delivering up to 5-A (LM73605-Q1) or 6-A (LM73606-Q1) DC load current

with exceptional efficiency and thermal performance in a very small solution size.

The LM73605-Q1/6-Q1 fixed-frequency peak current-mode control with configurable auto or FPWM operation

mode. Auto mode provides very high efficiency at light loads, and FPWM mode maintains constant switching

frequency over entire load range.

The device is internally compensated, which reduces design time and the number of external components. The

switching frequency is programmable from 350 kHz to 2.2 MHz by an external resistor. The LM73605-Q1/6-Q1

can also synchronize to an external clock within the same frequency range. The wide switching frequency

range allows the device to be optimized for a wide range of system requirements. It can be optimized for small

solution size with higher frequency; or for high efficiency with lower switching frequency. The LM73605-Q1/6-Q1

very low quiescent current, which is critical for battery-operated systems. It allows for a wide range of voltage

conversion ratios due to very small minimum on-time (t_ON-MIN) and minimum off-time (t_OFF-MIN). Automated

frequency foldback is employed at very high or low duty cycles to further extend the operating range.

The LM73605-Q1/6-Q1 also a power-good (PGOOD) flag, precision enable, internal or adjustable soft start, pre-

biased start-up, and output voltage tracking. Protection features include thermal shutdown, undervoltage lockout

(UVLO), cycle-by-cycle current limiting, and short-circuit hiccup protection. It provides flexible and easy-to-use

solutions for a wide range of applications.

The family requires very few external components and has a pin out designed for simple, optimum PCB layout

for enhanced EMI and thermal performance. The LM73605-Q1/6-Q1 devices are available in a 30-pin WQFN

leadless package.

8.2 Functional Block Diagram

ENABLE

VCC

BIAS

LDO

PVIN

I_SSC

Internal

SS

V_BOOT

Precision

Enable

CBOOT

V_CC

SS/TRK

HS I Sense

I_CMD

+

V_BOOTV_SW

EA

+

REF

œ

R_C

C_C

œ

+

UVLO

FB

UVLO

FB

V_SW

OV/UV

Detector

SW

PFM

Detector

CONTROL LOGIC

PGood

PGOOD

TSD

Hiccup

Detector

+

œ

Slope Comp

Oscillator

CLK

I_LIMIT

AGND

LS I Sense

FPWM

SYNC/

MODE

RT

PGND

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8.3 Feature Description

8.3.1 Synchronous Step-Down Regulator

The LM73605-Q1/6-Q1 synchronous buck with both power MOSFETs integrated in the device. Figure 8-1 shows

a simplified schematic for synchronous and non-synchronous buck converters. The synchronous buck integrates

both high-side (HS) and low-side (LS) power MOSFETs. The non-synchronous buck integrates HS MOSFET and

works with a discrete power diode as LS rectifier.

Synchronous

Buck

Non Synchronous

Buck

L

VIN

SW

V_OUT

C_OUT

V_OUT

V_IN

C_IN

V_IN

C_IN

C_OUT

PGND

Figure 8-1. Simplified Synchronous versus Non-synchronous Buck Converters

A synchronous converter with integrated HS and LS MOSFETs offers benefits such as the following:

•

Less design effort

Lower external component count

Reduced total solution size

Higher efficiency at heavier load

Easier PCB design

More control flexibility

The main advantage of a synchronous converter is that the voltage drop across the LS MOSFET is lower

than the voltage drop across the power diode of a non-synchronous converter. Lower voltage drop translates

into less power dissipation and higher efficiency. The LM73605-Q1/6-Q1 HS and LS MOSFETs with very low

on-time resistance to improve efficiency. It is especially beneficial when the output voltage is low. Because the

LS MOSFET is integrated into these devices, at light loads a synchronous converter has the flexibility to operate

in either discontinuous or continuous conduction mode.

An integrated LS MOSFET also allows the controller to obtain inductor current information when the LS switch

is on. It allows the control loop to make more complex decisions based on HS and LS currents. It allows the

LM73605-Q1/6-Q1 to have peak and valley cycle-by-cycle current limiting for more robust protection.

8.3.2 Auto Mode and FPWM Mode

The LM73605-Q1/6-Q1 pin-configurable auto mode or FPWM options.

In auto mode, the device operates in diode emulation mode (DEM) at light loads. In DEM, inductor current stops

flowing when it reaches 0 A. This is also referred to as discontinuous conduction mode (DCM). This is the same

behavior as the non-synchronous regulator, with higher efficiency. At heavier load, when the inductor current

valley is above 0 A, the device operates in continuous conduction mode (CCM), where the switching frequency

is fixed and set by RT pin.

In auto mode, the peak inductor current has a minimum limit, I_{PEAK_MIN}, in the LM73605-Q1/6-Q1. When peak

current reaches I_{PEAK_MIN}, the switching frequency reduces to regulate the required load current. Switching

frequency lowers when load reduces. This is when the device operates in pulse frequency modulation (PFM).

PFM further improves efficiency by reducing switching losses. Light load efficiency is especially important for

battery-operated systems.

In forced PWM (FPWM) mode, the device operates in CCM regardless of load with the frequency set by RT pin

or synchronization input. Inductor current can go negative at light loads. At light loads, the efficiency is lower

than auto mode, due to higher conduction losses and switching losses. In FPWM, the device has fixed switching

frequency over the entire load range, which is beneficial to noise sensitive applications.

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Figure 8-2 shows the inductor current waveforms in each mode with heavy load, light load, and very light load.

The difference between the two modes is at lighter loads where inductor current valley reaches zero.

Auto Mode

FPWM Mode

I_L

CCM

Heavy

Loads

t

I_L

Light

Loads

CCM

DCM

PFM

t

I_L

Very Light

Loads

t

Figure 8-2. Inductor Current Waveforms at Auto Mode and FPWM Mode with Different Loads

In CCM, the inductor current peak-to-peak ripple can be estimated by Equation 1:

(V_IN- V_OUT

f_SWì L

)

V_OUT

I_Lripple

=

ì

V

IN

(1)

The average or DC value of the inductor current equals the load current, or output current I_OUT, in steady state.

Peak inductor current can be calculated by Equation 2:

I_PEAK= I_OUT+ I_Lripple/ 2

(2)

Valley inductor current can be calculated by Equation 3:

I_VALLEY= I_OUT– I_Lripple/ 2

(3)

In auto mode, the CCM-to-DCM boundary condition is when I_VALLEY= 0 A. When I_Lripple≥ I_{PEAK_MIN}, the load

current at the DCM boundary condition can be found by Equation 4. When the peak-to-peak ripple current is

smaller than I_Lripple≥ I_PEAK-MIN, the PFM boundary is reached first.

I_{OUT_DCM}= I_Lripple/ 2

(4)

when

I_Lripple≥ I_{PEAK_MIN}

•

In auto mode, the PFM operation boundary condition is when I_PEAK= I_{PEAK_MIN}. Frequency foldback occurs

when peak current drops to I_{PEAK_MIN}, regardless of whether it is in CCM or DCM operation. When current ripple

is small, I_Lripple< I_{PEAK_MIN}, the peak current reaches I_{PEAK_MIN}when it is still in CCM. The output current at CCM

PFM boundary can be found by Equation 5:

I_{OUT_CCM_PFM}= I_{PEAK_MIN}– I_Lripple/ 2

(5)

when

I_Lripple< I_{PEAK_MIN}

•

The current ripple increases with reduced frequency if load reduces. When valley current reaches zero, the

frequency continues to fold back with constant peak current and discontinuous current.

In FPWM mode, there is no I_PEAK-MINlimit. The peak current is defined by Equation 2 at light loads and heavy

loads.

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Mode setting only affects operation at light loads. There is no difference if load current is above the DCM and

PFM boundary conditions discussed above.

See the Section 8.3.9 section for mode setting options in the LM73605-Q1/6-Q1.

8.3.3 Fixed-Frequency Peak Current-Mode Control

The LM73605-Q1/6-Q1 synchronous switched mode voltage regulator employs fixed frequency peak current

mode control with advanced features. The fixed switching frequency is controlled by an internal clock. To get

accurate DC load regulation, a voltage feedback loop is implemented to generate peak current command. The

HS switch is turned on at the rising edge of the clock. As shown in Figure 8-3, during the HS switch on-time, t_ON

,

the SW pin voltage, V_SW, swings up to approximately V_IN, and the inductor current, I_L, increases with a linear

slope. The HS switch is turned off when the inductor current reaches the peak current command. During the HS

switch off-time, t_OFF, the LS switch is turned on. Inductor current discharges through the LS switch, which forces

the V_SWto swing below ground by the voltage drop across the LS switch. The LS switch is turned off at the

next clock cycle, before the HS switch is turned on. The regulation loop adjusts the peak current command to

maintain a constant output voltage.

V

SW

D = t

/ T

SW

ON

V

IN

t

OFF

ON

0

t

-V

D

T

SW

I_L

I

L-PEAK

I

OUT

I

Lripple

I

L-VALLEY

0

t

Figure 8-3. SW Voltage and Inductor Current Waveforms in CCM

Duty cycle D is defined by the on-time of the HS switch over the switching period:

D = t_ON/ T_SW

where

(6)

•

T_SW= 1 / f_SWis the switching period

In an ideal buck converter where losses are ignored, D is proportional to the output voltage and inverse

proportional to the input voltage: D = V_OUT⁄ V_IN.

When the LM73605-Q1/6-Q1 set to operate in auto mode, the LS switch is turned off when its current reaches

zero ampere before the next clock cycle comes. Both HS switch and LS switch are off before the HS switch is

turned on at the next clock cycle.

8.3.4 Adjustable Output Voltage

The voltage regulation loop in the LM73605-Q1/6-Q1 the FB pin voltage to be the same as the internal reference

voltage. The output voltage of the LM73605-Q1/6-Q1 is set by a resistor divider to program the ratio from V_OUT

to V_FB. The resistor divider is connected from the output to ground with the mid-point connecting to the FB pin.

VOUT

R_FBT

FB

R_FBB

Figure 8-4. Output Voltage Setting by Resistor Divider

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The internal voltage reference and feedback loop produce precise voltage regulation over temperature. TI

recommends using divider resistors with 1% tolerance or better, and with temperature coefficient of 100 ppm or

lower. Typically, R_FBT= 10 kΩ to 100 kΩ is recommended. Larger R_FBTand R_FBBvalues reduce the quiescent

current going through the divider, which help maintain high efficiency at very light load. Larger divider values

also make the feedback path more susceptible to noise. If efficiency at very light load is critical in a certain

application, R_FBTup to 1 MΩ can be used.

R_FBBcan be calculated by Equation 7:

V_FB

R_FBB

=

R_FBT

V_OUT- V_FB

(7)

The minimum programmable V_OUTequals V_FB, with R_FBBopen. The maximum V_OUTis limited by the maximum

duty cycle at a given frequency:

D_MAX= 1 – (t_OFF-MIN/ T_SW

)

(8)

where

•

t_OFF-MINis the minimum off time of the HS switch

T_SW= 1 / f_SWis the switching period

Ideally, without frequency foldback, V_{OUT_MAX}= V_{IN_MIN}× D_MAX

.

Power losses in the circuit reduces the maximum output voltage. The LM73605-Q1/6-Q1 back switching

frequency under t_{OFF_MIN}condition to further extend V_{OUT_MAX}. The device maintains output regulation with

lower input voltage. The minimum foldback frequency is limited by the maximum HS on-time, t_{ON_MAX}. Maximum

output voltage with frequency foldback can be estimated by:

t_ON-MAX

t_ON-MAX+ t_OFF-MIN

V_{OUT _MAX}= V

ì

- I_OUTì (R_{DS_ON_HS}+ DCR)

IN_MIN

(9)

The voltage drops on the HS MOSFET and inductor DCR have been taken into account in Equation 9. The

switching losses were not included.

If the resistor divider is not connected properly, the output voltage cannot be regulated because the feedback

loop cannot obtain correct output voltage information. If the FB pin is shorted to ground or disconnected, the

output voltage is driven close to V_IN. The load connected to the output can be damaged under this condition. Do

not short FB to ground or leave it open circuit during operation.

The FB pin is a noise sensitive node. It is important to place the resistor divider as close as possible to the FB

pin, and route the feedback node with a short and thin trace. The trace connecting V_OUTto R_FBTcan be long,

but it must be routed away from the noisy area of the PCB. For more layout recommendations, see the Section 9

section.

8.3.5 Enable and UVLO

The LM73605-Q1/6-Q1 output voltage when the VCC voltage is higher than the undervoltage lock out (UVLO)

level, V_{CC_UVLO}, and the EN voltage is higher than V_{EN_VOUT_H}

.

The internal LDO output voltage VCC is turned on when the EN voltage is higher than V_{EN_VCC_H}. The precision

enable circuitry is also turned on when VCC is above UVLO. Normal operation of the LM73605-Q1/6-Q1 with

regulated output voltage is enabled when the EN voltage is greater than V_{EN_VOUT_H}. When the EN voltage is

less than V_{EN_VCC_L}, the device is in shutdown mode. The internal dividers make sure V_{EN_VOUT_H}is always

higher than V_{EN_VCC_H}

.

The EN pin cannot be left floating. The simplest way to enable the operation of the LM73605-Q1/6-Q1 is to

connect the EN pin to PVIN, which allows self-start-up of the LM73605-Q1/6-Q1 when V_INrises. Use of a pullup

resistor between PVIN and EN pins helps reduce noise coupling from PVIN pin to the EN pin.

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Many applications benefit from employing an enable divider to establish a customized system UVLO. This can

be used either for sequencing, system timing requirement, or to reduce the occurrence of deep discharge of a

battery power source. Figure 8-5 shows how to use a resistor divider to set a system UVLO level. An external

logic output can also be used to drive the EN pin for system sequencing.

VIN

R_ENT

ENABLE

R_ENB

Figure 8-5. System UVLO

With a selected R_ENT, the R_ENBcan be calculated by:

V_{EN_ VOUT _H}

R_ENB

=

R_ENT

V

- V_{EN_VOUT_H}

IN_ON_H

(10)

where

V_{IN_ON_H}is the desired supply voltage threshold to turn on this device

•

Note that the divider adds to supply quiescent current by V_IN/ (R_ENT+ R_ENB). Small R_ENTand R_ENBvalues add

more quiescent current loss. However, large divider values make the node more sensitive to noise. R_ENTin the

hundreds of kΩ range is a good starting point.

8.3.6 Internal LDO, V_{CC_UVLO}, and BIAS Input

The LM73605-Q1/6-Q1 an internal LDO, generating VCC voltage for control circuitry and MOSFET drivers. The

VCC pin must have a 1-µF to 4.7-µF bypass capacitor placed as close as possible to the pin and properly

grounded. Do not load the VCC pin or short it to ground during operation. Shorting VCC pin to ground during

operation can damage the device.

The UVLO on VCC voltage, V_{CC_UVLO}, turns off the regulation when VCC voltage is too low. It prevents the

LM73605-Q1/6-Q1 from operating until the VCC voltage is enough for the internal circuitry. Hysteresis on

V_{CC_UVLO}prevents the part from turning off during power up if V_INdroops due to input current demands. The

LDO generates VCC voltage from one of the two inputs: the supply voltage V_IN, or the BIAS input. When BIAS

is tied to ground, the LDO input is V_IN. When BIAS is tied to a voltage higher than 3.3 V, the LDO input is V_BIAS

BIAS voltage must be lower than both V_INand 18 V.

.

The BIAS input is designed to reduce the LDO power loss. The LDO power loss is:

P

_{LOSS_LDO}= I_LDO× (V_{IN_LDO}– V_{OUT_LDO})

(11)

The higher the difference between the input and output voltages of the LDO, the more loss occurs to supply the

same LDO output current. The BIAS input provides an option to supply the LDO with a lower voltage than V_IN,

to reduce the difference of the input and output voltages of the LDO and reduce power loss. For example, if the

LDO current is 10 mA at a certain frequency with V_IN= 24 V and V_OUT= 5 V. The LDO loss with BIAS tied to

ground is equal to 10 mA × (24 V – 3.27 V) = 207.3 mW, while the loss with BIAS tied to V_OUTis equal to 10 mA

× (5 – 3.27) = 17.3 mW.

The efficiency improvement is more significant at light and mid loads because the LDO loss is a higher

percentage in the total loss. The improvements is more significant with higher switching frequency because

the LDO current is higher at higher switching frequency. The improvement is more significant when V_IN» V_OUT

because the voltage difference is higher.

Figure 8-6 and Figure 8-7 show efficiency improvement with bias tied to V_OUTin a V_OUT= 5 V and f_SW= 2200

kHz application, in auto mode and FPWM mode, respectively.

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100

95

90

85

80

75

70

65

60

55

100

80

60

40

20

0

VIN = 12 V BIAS = VOUT

VIN = 12 V BIAS = GND

VIN = 24 V BIAS = VOUT

VIN = 24 V BIAS = GND

VIN = 12 V BIAS = VOUT

50

45

40

35

30

VIN = 12 V BIAS = GND

VIN = 24 V BIAS = VOUT

VIN = 24 V BIAS = GND

0.001

0.01 0.02 0.05 0.1 0.2 0.5

Load Current (A)

1

2

3 456

0.001

0.010.02 0.05 0.1 0.2 0.5

Load Current (A)

1

2

3 45 7 10

EFF_

V_OUT= 5 V

f_SW= 2200 kHz

Auto Mode

V_OUT= 5 V

f_SW= 2200 kHz

FPWM Mode

Figure 8-6. LM73606-Q1 Efficiency Comparison

With Bias = V_OUTto Bias = GND in Auto Mode

Figure 8-7. LM73606-Q1 Efficiency Comparison

With Bias = V_OUTto Bias = GND in FPWM Mode

TI recommends tying the BIAS pin to V_OUTwhen V_OUTis equal to or greater than 3.3 V and no greater than 18 V.

Tie the BIAS pin to ground when not in use. A ceramic capacitor, C_BIAS, can be used from the BIAS pin to ground

for bypassing. If V_OUThas high frequency noise or spikes during transients or fault conditions, a resistor (1 to 10

Ω) connected between V_OUTto BIAS can be used together with C_BIASfor filtering.

The VCC voltage is typically 3.27 V. When the LM73605-Q1/6-Q1 operating in PFM mode with frequency

foldback, VCC voltage is reduced to 3.1 V (typical) to further decrease the quiescent current and improve

efficiency at very light loads. Figure 8-8 shows an example of VCC voltage change with mode change.

3.5

3.4

3.3

3.2

3.1

3

2.9

2.8

2.7

2.6

2.5

2.4

2.3

2.2

2.1

2

Auto Mode

FPWM Mode

0.001

0.01 0.02 0.05 0.1 0.2

Load Current (A)

0.5

1

2 3 45

VCC_

V_OUT= 5 V

f_SW= 500 kHz

V_IN= 12 V

Figure 8-8. VCC Voltage versus Load Current

VCC voltage has an internal UVLO threshold, V_{CC_UVLO}. When VCC voltage is higher than V_{CC_UVLO}rising

threshold, the device is active and in normal operation if V_EN> V_{EN_VOUT_H}. If VCC voltage droops below

V_{CC_UVLO}falling threshold, the V_OUTis shut down.

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8.3.7 Soft Start and Voltage Tracking

The LM73605-Q1/6-Q1 controlled output voltage ramp during start-up. The soft-start feature reduces inrush

current during start-up and improves system performance and reliability.

If the SS/TRK pin is floating, the LM73605-Q1/6-Q1 up following the fixed internal soft-start ramp.

If longer soft-start time is desired, an external capacitor can be added from SS/TRK pin to ground. There is a

2-µA (typical) internal current source, I_SSC, to charge the external capacitor. For a desired soft-start time t_SS

capacitance of C_SScan be found by Equation 12.

,

C_SS= I_SSC× t_SS

(12)

where

•

C_SS= soft-start capacitor value (F)

I_SSC= soft-start charging current (A)

t_SS= desired soft-start time or times

The FB voltage always follows the lower potential of the internal voltage ramp or the voltage on the SS/TRK pin.

Thus, the soft-start time can only be extended longer than the internal soft-start time by connecting C_SS. Use

C_SSto extend soft-start time when there are a large amount of output capacitors, the output voltage is high, or

the output is heavily loaded during start-up.

LM73605-Q1/6-Q1 operating in diode emulation mode during start-up regardless of mode setting. The device is

capable of starting up into pre-biased output conditions. During start-up, the device sets the minimum inductor

current to zero to avoid back charging the input capacitors.

LM73605-Q1/6-Q1 can track an external voltage ramp applied to the SS/TRK pin, if the ramp is slower than

the internal soft-start ramp. The external ramp final voltage after start-up must be greater than 1.5 V to avoid

noise interfering with the reference voltage. Figure 8-9 shows how to use resistor divider to set V_OUTto follow an

external ramp.

EXT RAMP

R_TRT

SS/TRK

R_TRB

Figure 8-9. Soft-start Tracking External Ramp

V_OUTtracking also provides the option of ramping up faster than the internal start-up ramp. The FB voltage

always follows the lower potential of the internal voltage ramp and the voltage on the SS/TRK pin. Figure 8-10

shows the case when V_OUTramps slower than the internal ramp, while Figure 8-11 shows when V_OUTramps

faster than the internal ramp. If the tracking ramp is delayed after the internal ramp is completed, V_FBfollows the

tracking ramp even if it is faster than the internal ramp. Faster start-up time may result in large inductor current

during start-up. Use with special care.

Enable

Internal SS Ramp

Ext Tracking Signal to SS pin

V_OUT

Figure 8-10. Tracking With Longer Start-up Time Than the Internal Ramp

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Enable

Internal SS Ramp

Ext Tracking Signal to SS pin

V_OUT

Figure 8-11. Tracking With Shorter Start-up Time Than the Internal Ramp

The SS/TRK pin is discharged to ground by an internal pulldown resistor R_SSDwhen the output voltage is

shutting down, such as in the event of UVLO, thermal shutdown, hiccup, or V_EN= 0. If a large C_SSis used, and

the time when V_EN= 0 V is very short, the C_SSmay not be fully discharged before the next soft start. Under this

condition, the FB voltage follows the internal ramp slew rate until the voltage on C_SSis reached, then follow the

slew rate defined by C_SS

.

8.3.8 Adjustable Switching Frequency

The internal oscillator frequency is controlled by the impedance on the RT pin. If the RT pin is open circuit, the

LM73605-Q1/6-Q1 at default switching frequency, 500 kHz. The RT pin is not designed to be connected directly

to ground. To program the switching frequency by R_Tresistor, Equation 13, or Figure 8-12, or Table 8-1 can be

used to find the resistance value.

1

R_T(kW) =

f_SW(kHz) ì 2.675 ì 10^-5- 0.0007

(13)

120

110

100

90

80

70

60

50

40

30

20

10

200 400 600 800 1000 1200 1400 1600 1800 2000 2200

Frequency (kHz)

RT_F

Figure 8-12. R_TResistance versus Switching Frequency

Table 8-1. Typical Frequency Setting Resistance

SWITCHING FREQUENCY f_SW(kHz)

R_TRESISTANCE (kΩ)

350

400

115

100

500

78.7 (or open)

52.3

750

1000

1500

2000

2200

39.2

26.1

19.1

17.4

The choice of switching frequency is usually a compromise between conversion efficiency and the size of the

solution. Lower switching frequency has lower switching losses (including gate charge losses, switch transition

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losses, and so forth) and usually results in higher overall efficiency. However, higher switching frequency allows

the use of smaller power inductor and output capacitors, hence a more compact design. Lower inductance

also helps transient response (higher large signal slew rate of inductor current), and has lower DCR. The

optimal switching frequency is usually a trade-off in a given application and thus needs to be determined on a

case-by-case basis. The following are factors that need to be taken into account:

•

Input voltage range

Output voltage

Most frequent load current level or levels

External component choices

Solution size/cost requirements

Efficiency

Thermal management requirements

The choice of switching frequency can also be limited whether an operating condition triggers t_ON-MINor t_OFF-MIN

.

Minimum on-time, t_ON-MIN, is the smallest time that the HS switch can be on. Minimum off-time, t_OFF-MIN, is the

smallest duration that the HS switch can be off.

In CCM operation, t_ON-MINand t_{OFF_MIN}limit the voltage conversion range given a selected switching frequency,

f_SW. The minimum duty cycle allowed is:

D_MIN= t_ON-MIN× f_SW

(14)

The maximum duty cycle allowed is:

D_MAX= 1 – t_OFF-MIN× f_SW

(15)

Given an output voltage, the choice of the switching frequency affects the allowed input voltage range, solution

size and efficiency. The maximum operational supply voltage can be found by:

V_{IN_MAX}= V_OUT/ (f_SW× t_ON-MIN

)

(16)

At lower supply voltage, the switching frequency decreases once t_OFF-MINis tripped. The minimum V_INwithout

frequency foldback can be approximated by:

V_{IN_MIN}= V_OUT/ (1 – f_SW× t_OFF-MIN

)

(17)

With a desired V_OUT, the range of allowed V_INis narrower with higher switching frequency.

The LM73605-Q1/6-Q1 an advanced frequency foldback algorithm under both t_{ON_MIN}and t_{OFF_MIN}conditions.

With frequency foldback, stable output voltage regulation is extended to wider range of supply voltages.

At very high V_INconditions where t_ON-MINlimitation is met, the switching frequency reduces to allow higher V_IN

while maintaining V_OUTregulation. Note that the peak-to-peak inductor current ripple will increase with higher

V_INand lower frequency. TI does not recommend designing the circuit to operate with t_{ON_MIN}under typical

conditions.

At very low V_INconditions, where t_OFF-MINlimitation is met, the switching frequency decreases until t_ON-MAX

condition is met. Such frequency foldback mechanism allows the LM73605-Q1/6-Q1 to have very low dropout

voltage regardless of frequency setting.

8.3.9 Frequency Synchronization and Mode Setting

The LM73605-Q1/6-Q1 switching action can synchronize to an external clock from 350 kHz to 2.2 MHz. TI

recommends connecting the external clock to the SYNC/MODE pin with an appropriate termination resistor.

Ground the SYNC/MODE pin if not used.

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SYNC/

MODE

EXT CLOCK

R

SYNC

Figure 8-13. Frequency Synchronization

Recommendations for the external clock include a high level no lower than 2 V, low level no higher than

0.4 V, duty cycle between 10% and 90%, and both positive and negative pulse width no shorter than 80 ns.

When the external clock fails at logic high or low, the LM73605-Q1/6-Q1 at the frequency programmed by the

R_Tresistor after a time-out period. TI recommends connecting a resistor to the RT pin such that the internal

oscillator frequency is the same as the external clock frequency. This allows the regulator to continue operating

at approximately the same switching frequency if the external clock fails with the same control loop behavior.

The SYNC/MODE pin is also used as an operation mode control input.

•

To set the operation in auto mode, connect SYNC/MODE pin to ground, or a logic signal lower than 0.3 V.

To set the operation in FPWM mode, connect SYNC/MODE pin to a bias voltage or logic signal greater than

0.6 V.

•

When the LM73605-Q1/6-Q1 synchronized to an external clock, the operation mode is FPWM.

Table 8-2 summarizes the operation mode and features according to the SYNC/MODE input signal. For more

details, see the Section 8.4.3 and Section 8.3.2 sections.

Table 8-2. SYNC/MODE Pin Settings and Operation Modes

SYNC/MODE

INPUT

SWITCHING

FREQUENCY

OPERATING

MODE

LIGHT LOAD BEHAVIOR

•

No negative inductor current, device operates in discontinuous conduction mode

(DCM) when current valley reaches 0 A.

Minimum peak inductor current is limited at I_{PEAK_MIN}; device operates in pulse

Logic low

Set by R_Tresistor

Auto mode

frequency modulation (PFM) mode when peak current reaches I_{PEAK_MIN}

.

Switching frequency reduces in PFM mode.

Logic high

•

Fixed frequency continuous conduction mode (CCM) regardless of load

Inductor current have negative portion at light loads

No I_{PEAK_MIN}

FPWM mode

Set by external

clock

External clock

8.3.10 Internal Compensation and C_FF

The LM73605-Q1/6-Q1 internally compensated. The internal compensation is designed such that the loop

response is stable over a wide operating frequency and output voltage range. The internal R-C values are 500

kΩ and 30 pF, respectively.

When large resistance value (MΩ) is used for R_FBT, the pole formed by an internal parasitic capacitor and R_FBT

can be low enough to reduce the phase margin. If only low ESR output capacitors (ceramic types) are used for

C_OUT, the control loop can have low phase margin. To provide a phase boost an external feedforward capacitor

(C_FF) can be added in parallel with R_FBT. Choose the C_FFcapacitor to provide most phase boost at the estimated

crossover frequency f_X:

K

f_X

=

V_OUTì C_OUT

(18)

where

•

K = 20.27 with LM73605-Q1

K = 24.16 with LM73606-Q1

Select C_OUTso that the f_Xis no higher than 1/6 of the switching frequency. Typically, f_X/ f_SW= 1/10 to 1/8

provides a good combination of stability and performance.

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Place the external feedforward capacitor in parallel with the top resistor divider R_FBTwhen additional phase

boost is needed.

VOUT

R_FBT

C_FF

FB

R_FBB

Figure 8-14. Feedforward Capacitor for Loop Compensation

The feedforward capacitor C_FFin parallel with R_FBTplaces an additional zero before the crossover frequency of

the control loop to boost phase margin. The zero frequency can be found by Equation 19:

f_Z-CFF= 1 / (2π × R_FBT× C_FF

)

(19)

An additional pole is also introduced with C_FFat the frequency of:

f_P-CFF= 1 / (2π × C_FF× (R_FBT// R_FBB))

(20)

Select the C_FFso that the bandwidth of the control loop without the C_FFis centered between f_Z-CFFand f_P-CFF

.

The zero at f_Z-CFFadds phase boost at the crossover frequency and improves transient response. The pole at

f_P-CFFhelps maintain proper gain margin at frequency beyond the crossover.

The need of C_FFdepends on R_FBTand C_OUT. Typically, choose R_FBT≤ 100 kΩ. C_FFmay not be required,

because the internal parasitic pole is at higher frequency. If C_OUThas larger ESR, and ESR zero f_Z-ESR= 1 / (2π

× ESR × C_OUT) is low enough to provide phase boost around the crossover frequency, do not use C_FF. Equation

21 was tested for ceramic output capacitors:

1

C_FF

=

ì

2 ì p ì f_x

R_FBTì (R_FBT// R_FBB

)

(21)

The C_FFcreates a time constant with R_FBTthat couples in the attenuated output voltage ripple to the FB node. If

the C_FFvalue is too large, it can couple too much ripple to the FB and affect V_OUTregulation. It can also couple

too much transient voltage deviation and falsely trigger PGOOD flag.

8.3.11 Bootstrap Capacitor and V_BOOT-UVLO

The driver of the HS switch requires a bias voltage higher than the V_INvoltage. The capacitor, C_BOOTin the

Figure 3-1, connected between CBOOT and SW pins works as a charge pump to boost voltage on the CBOOT

pin to (V_SW+ V_CC). A boot diode is integrated on the die to minimize external component count. TI recommends

a high-quality 0.47-µF, 6.3-V or higher voltage ceramic capacitor for C_BOOT. The V_{BOOT_UVLO}threshold is

designed to maintain proper HS switch operation. If the C_BOOTis not charged above this voltage with respect to

SW, the device initiates a charging sequence using the LS switch before turning on the HS switch.

8.3.12 Power-Good and Overvoltage Protection

The LM73605-Q1/6-Q1 a built-in power-good (PGOOD) flag to indicate whether the output voltage is at an

appropriate level or not. The PGOOD flag can be used for start-up sequencing of multiple rails. The PGOOD pin

is an open-drain output that requires a pullup resistor to an appropriate logic voltage (any voltage below 15 V).

The pin can sink 5 mA of current and maintain its specified logic low level. A typical pullup resistor value is 10

kΩ to 100 kΩ. When the FB voltage is higher than V_PGOOD-OVor lower than V_PGOOD-UVthreshold, the PGOOD

internal switch is turned on, and the PGOOD pin voltage is pulled low. When the FB is within the range, the

PGOOD switch is turned off, and the pin is pulled up to the voltage connected to the pullup resistor. The PGOOD

function also has a deglitch timer for about 140 µs for each transition. If it is desired to pull up PGOOD pin to a

voltage higher than 15 V, a resistor divider can be used to divide the voltage down.

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V_PU

R_PGT

PGOOD

R_PGB

Figure 8-15. Divider for PGOOD Pullup Voltage

With a given pullup voltage V_PU, select a desired voltage on the PGOOD pin, V_PG. With a selected R_PGT, the

R_PGBcan be found by:

V_PG

R_PGB

=

R_PGT

V_PU- V_PG

(22)

When the device is disabled, the output voltage is low, and the PGOOD flag indicates logic low as long as V_IN

2 V.

>

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8.3.13 Overcurrent and Short-Circuit Protection

The LM73605-Q1/6-Q1 protected from overcurrent conditions with cycle-by-cycle current limiting on both HS and

LS MOSFETs.

The HS switch is turned off when HS current goes beyond the peak current limit, I_HS-LIMIT. The LS switch can

only be turned off when LS current is below LS current limit, I_LS-LIMIT. If the LS switch current is higher than

I_LS-LIMITat the end of a switching cycle, the switching cycle is extended until the LS current reduces below the

limit.

Current limiting on both HS and LS switches provides tighter control of the maximum DC inductor current, or

output current. They also help prevent runaway current at extreme conditions. With the LM73605-Q1/6-Q1, the

maximum output current is always limited to:

I_{DC_LIMIT}= (I_{HS_LIMIT}+ I_{LS_LIMIT}) / 2

(23)

The LM73605-Q1/6-Q1 hiccup current protection at extreme overload conditions, including short-circuit

condition. Hiccup is only activated when V_OUTdroops below 40% (typical) of the regulation voltage and stays

below for 128 consecutive switching cycles. Under overcurrent conditions when V_OUThas not fallen below 40%

of regulation, the LM73605-Q1/6-Q1 operation with cycle-by-cycle HS and LS current limiting.

Hiccup is disabled during soft start. When hiccup is triggered, the device turns off V_OUTregulation and re-tries

soft start after a re-try delay time, T_OC= 46 ms (typical). The long wait time allows the device, and the load, to

cool down under such fault conditions. If the fault condition still exists when re-try, hiccup shuts down the device

and repeats the wait and re-try cycle. If the fault condition has been removed, the device starts up normally.

If tracking was used for initial sequencing, the device restarts using the internal soft-start ramp. Hiccup mode

helps reduce the device power dissipation and die temperature under severe overcurrent conditions and short

circuits. It improves system reliability and prolongs the life span of the device.

In FPWM mode, negative current protection is implemented to protect the switches from extreme negative

currents. When LS switch current reaches I_NEG-LIMIT, LS switch turns off, and HS switch turns on to conduct the

negative current. HS switch is turned off once its current reaches 0 A.

8.3.14 Thermal Shutdown

Thermal shutdown protection prevents the device from extreme junction temperature. The device is turned off

when the junction temperature exceeds 160°C (typical). After thermal shutdown occurs, hysteresis prevents

the device from switching until the junction temperature drops to approximately 135°C. When the junction

temperature falls below 135°C, the LM73605-Q1/6-Q1.

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8.4 Device Functional Modes

8.4.1 Shutdown Mode

The EN pin provides electrical on/off control of the device. When the EN pin voltage is below V_{EN_VCC_L}, the

device is in shutdown mode. The LDO output voltage V_CC= 0 V and the output voltage V_OUT= 0 V. In shutdown

mode, the quiescent current drops to a very low value.

8.4.2 Standby Mode

The internal LDO has a lower EN threshold than that required to start the regulator. When the EN pin voltage

is above V_{EN_VCC_H}, the internal LDO regulates the VCC voltage. The precision enable circuitry is turned on

once V_CCis above V_{CC_UVLO}. The device is in standby mode if EN voltage is below V_{EN_VOUT_H}. The internal

MOSFETs remains in tri-state unless the voltage on EN pin goes beyond V_{EN_VOUT_H}threshold. The LM73605-

Q1/6-Q1 also UVLO protection. If the VCC voltage is below the V_{CC_UVLO}level, the output of the regulator is

turned off.

8.4.3 Active Mode

The LM73605-Q1/6-Q1 in active mode when the EN voltage is above V_{EN_VOUT_H}, and V_CCis above V_{CC_UVLO}

.

The simplest way to enable the operation of the LM73605-Q1/6-Q1 is to pull up the EN pin to PVIN, which allows

self-start-up when the input voltage ramps up.

In active mode, depending on the load current and mode setting, the LM73605-Q1/6-Q1 in one of four modes:

1. CCM with fixed switching frequency when load current is above half of the peak-to-peak inductor current

ripple

2. DCM with fixed switching frequency when load current is lower than half of the peak-to-peak inductor current

ripple in CCM operation

3. PFM when switching frequency is decreased at very light load

4. Under overcurrent or overtemperature conditions, the device operates in one of the fault protection modes

See Table 8-2 for mode-setting details.

8.4.3.1 CCM Mode

In CCM operation, inductor current has a continuous triangular waveform. The HS switch is on at the beginning

of a switching cycle and the LS switch is turned off the end of each switching cycle. In auto mode, the

LM73605-Q1/6-Q1 in CCM when the load current is higher than ½ of the peak-to-peak inductor current (I_Lripple).

In FPWM mode, the LM73605-Q1/6-Q1 in CCM, regardless of load.

In CCM operation, the switching frequency is typically constant, unless t_ON-MIN, t_OFF-MIN, or I_PEAK-MINconditions

are met. The constant switching frequency is determined by RT pin setting, or the external synchronization clock

frequency. The duty cycle is also constant in CCM: D = V_OUT/ V_INif loss is ignored, regardless of load. The

peak-to-peak inductor ripple is constant with the same V_INand V_OUT, regardless of load.

With very high or very low supply voltages, when the t_ON-MINor t_OFF-MINcondition is met, the frequency reduces

to maintain V_OUTregulation with even higher or lower V_IN, respectively. When the I_{PEAK_MIN}condition is met in

auto mode, the switching frequency folds back to provide higher efficiency. I_{PEAK_MIN}is disabled in FPWM mode.

8.4.3.2 DCM Mode

DCM operation only happens in auto mode when the load current is lower than half of the CCM inductor current

ripple, and peak current is higher than I_PEAK-MIN. There is no DCM in FPWM mode. DCM is also known as

diode emulation mode. The LS FET is turned off when the inductor current ramps to 0 A. DCM has the same

switching frequency as CCM, which is set by the RT pin. Duty cycle and peak current reduces with lighter load in

DCM. DCM is more efficient than FPWM under the same condition, because of lower switching losses and lower

conduction losses. When the peak current reduces to I_{PEAK_MIN}at lighter load, the LM73605-Q1/6-Q1 in PFM

mode.

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8.4.3.3 PFM Mode

Pulse-frequency-modulation (PFM) mode is activated when peak current is lower than I_PEAK-MIN, only in auto

mode. Peak current is kept constant and V_OUTis regulated by frequency. Efficiency is greatly improved by

lowered switching losses, especially at very light loads.

In PFM operation, a small DC positive offset appears on V_OUT. The lower the frequency is folded back in PFM,

the more the DC offset is on V_OUT. See the V_OUTregulation curves in the Section 9.2.3. If the DC offset on V_OUT

is not acceptable, a dummy load at V_OUT, or lower R_FBTand R_FBBresistance values can be used to reduce the

offset. Alternatively, the device can be run in FPWM mode where the switching frequency is constant, and no

offset is added to affect the V_OUTaccuracy unless t_{ON_MIN}is reached.

8.4.3.4 Fault Protection Mode

The LM73605-Q1/6-Q1 hiccup current protection at extreme overload and short circuit conditions. Hiccup is

activated when V_OUTdroops below 40% (typical) of the regulation voltage and stays for 128 consecutive

switching cycles. Hiccup is disabled during soft start. In hiccup, the device turns off V_OUTand re-tries soft start

after 46-ms wait time. Cycle repeats until overcurrent fault condition has been removed. Hiccup mode helps

reduce the device power dissipation and die temperature under severe overcurrent conditions and short circuits.

It improves system reliability and prolongs the life span of the device.

Under overcurrent conditions when V_OUTdroops below regulation but above 40% of regulated voltage, the

LM73605-Q1/6-Q1 in cycle-by-cycle HS and LS current limiting protection mode.

Thermal shutdown prevents the device from extreme junction temperature by turning off the device when the

junction temperature exceeds 160°C (typical). After thermal shutdown occurs, hysteresis prevents the device

from switching until the junction temperature drops to approximately 135°C. When the junction temperature falls

below 135°C, the LM73605-Q1/6-Q1.

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Application and Implementation

Note

Information in the following applications sections is not part of the TI component specification, and

TI does not warrant its accuracy or completeness. TI’s customers are responsible for determining

suitability of components for their purposes. Customers should validate and test their design

implementation to confirm system functionality.

9.1 Application Information

The LM73605-Q1/6-Q1 step-down DC-DC voltage regulators. It is designed to operate with a wide supply

voltage range (3.5 V to 36 V), wide switching frequency range (350 kHz to 2.2 MHz), and wide output

voltage range: up to 95% V_IN. The LM73605-Q1/6-Q1 synchronous with both HS and LS MOSFETs integrated,

and it is capable of delivering a maximum output current of 5 A (LM73605-Q1) or 6 A (LM73606-Q1). The

following design procedure can be used to select component values for the LM73605-Q1/6-Q1. Alternately, the

WEBENCH® software may be used to generate a complete design. The WEBENCH® software uses an iterative

design procedure and accesses a comprehensive database of components when generating a design (see

Section 9.2.2.1). This section presents a simplified discussion of the design process.

9.2 Typical Application

The LM73605-Q1/6-Q1 only a few external components to perform high-efficiency power conversion, as shown

in Figure 9-1.

L

V_IN

V_OUT

SW

PVIN

EN

C_BOOT

C_OUT

C_IN

CBOOT

BIAS

RT

PGND

PGOOD

SS/TRK

R_FBT

SYNC/

MODE

FB

R_FBB

VCC

C_VCC

AGND

Figure 9-1. LM73605-Q1/6-Q1 Basic Schematic

The LM73605-Q1/6-Q1 also many practical features to meet a wide range of system design requirements and

optimization, such as UVLO, programmable soft-start time, start-up tracking, programmable switching frequency,

clock synchronization, and a power-good flag. Note that for ease of use, the feature pins do not require an

additional component when not in use. They can be either left floating or shorted to ground. Please refer to the

Section 6 for details.

A comprehensive schematic with all features utilized is shown in Figure 9-2.

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V_IN

R_ENT

L

C_IN

V_OUT

PVIN

PGND

EN

SW

C_OUT

C_BOOT

CBOOT

BIAS

R_ENB

SS/TRK

RT

PGOOD

FB

C_SS

R_FBT

R_FBB

R_T

AGND

VCC

SYNC/

MODE

C_VCC

R_SYNC

Figure 9-2. LM73605-Q1/6-Q1 Comprehensive Schematic with All Features Utilized

The external components must fulfill not only the needs of the power conversion, but also the stability criteria

of the control loop. The LM73605-Q1/6-Q1 optimized to work with a range of external components. For quick

component selection, Table 9-1 can be used.

Table 9-1. Typical Component Selection

f_SW(kHz)

350

V_OUT(V)

L (µH)

2.2

1.5

0.68

0.47

4.7

3.3

1.8

1.2

6.8

4.7

3.3

2.2

15

C_OUT(µF)⁽¹⁾

500

400

200

100

200

150

88

R_FBT(kΩ)

100

R_FBB(kΩ)

OPEN

43.5

25

R_T(kΩ)

115

1

500

78.7 or open

39.2

1000

2200

350

1

17.4

3.3

5

115

500

78.7 or open

39.2

1000

2200

350

44

17.4

120

88

115

500

5

25

78.7 or open

39.2

1000

2200

350

5

66

25

5

44

25

17.4

12

24

66

9.1

115

500

10

44

9.1

78.7 or open

39.2

1000

350

6.8

22

9.1

40

4.3

115

500

15

30

4.3

78.7 or open

(1) All the C_OUTvalues are after derating. Add more when using ceramics.

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9.2.1 Design Requirements

Detailed design procedure is described based on a design example. For this design example, use the

parameters listed in Table 9-2.

Table 9-2. Design Example Parameters

DESIGN PARAMETER

Typical input voltage

Output voltage

VALUE

12 V

5 V

Output current

5 A

Operating frequency

Soft-start time

500 kHz

11 ms

9.2.2 Detailed Design Procedure

9.2.2.1 Custom Design With WEBENCH® Tools

To create a custom design with the WEBENCH® Power Designer, click the LM73605-Q1 or LM73606-Q1

device.

1. Start by entering the input voltage (V_IN), output voltage (V_OUT), and output current (I_OUT) requirements.

2. Optimize the design for key parameters such as efficiency, footprint, and cost using the optimizer dial.

3. Compare the generated design with other possible solutions from Texas Instruments.

The WEBENCH Power Designer provides a customized schematic along with a list of materials with real-time

pricing and component availability.

In most cases, these actions are available:

•

Run electrical simulations to see important waveforms and circuit performance

Run thermal simulations to understand board thermal performance

Export customized schematic and layout into popular CAD formats

Print PDF reports for the design, and share the design with colleagues

Get more information about WEBENCH tools at www.ti.com/WEBENCH.

9.2.2.2 Output Voltage Setpoint

The output voltage of the LM73605-Q1/6-Q1 externally adjustable using a resistor divider network. The divider

network is comprised of top feedback resistor, R_FBT, and bottom feedback resistor, R_FBB. Use Equation 24 to

determine the output voltage of the converter.

≈

∆

«

’

÷

◊

R_FBT

R_FBB

V_OUT= V_FB

ì

1+

(24)

Typically, R_FBT= 10 kΩ to 100 kΩ is recommended. Larger R_FBTand R_FBBvalues reduce the quiescent current

going through the divider, which help maintain high efficiency at very light loads. Larger divider values also make

the feedback path more susceptible to noise. If efficiency at very light loads is critical in a certain application,

R_FBTup to 1 MΩ can be used.

V_FB

R_FBB

=

R_FBT

V_OUT- V_FB

(25)

R_FBT= 100 kΩ is selected here. R_FBB= 24.99 kΩ can be calculated to get 5-V output voltage.

9.2.2.3 Switching Frequency

The default switching frequency of the LM73605-Q1/6-Q1 set at 500 kHz. For this design, the RT pin can be

floating, and the LM73605-Q1/6-Q1 at 500 kHz in CCM mode. An R_Tresistor of 78.7 kΩ, calculated using

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Equation 13, Figure 8-12, or Table 8-1, can be connected from RT pin to ground to obtain 500-kHz operation

frequency as well.

The LM73605-Q1/6-Q1 switching action can synchronize to an external clock from 350 kHz to 2.2 MHz. TI

recommends connecting an external clock to the SYNC/MODE pin with a 50-Ω to 100-Ω termination resistor.

The SYNC/MODE pin must be grounded if not used.

RT pin is floating and SYNC/MODE pin is tied to ground in this design.

9.2.2.4 Input Capacitors

The LM73605-Q1/6-Q1 high-frequency ceramic input decoupling capacitors. Depending on the application, a

bulk input capacitor can also be added. The typical recommended ceramic decoupling capacitors include one

small, 0.1 µF to 1 µF, and one large, 10 µF to 22 µF, capacitors. TI recommends high-quality ceramic type X5R

or X7R capacitors. The voltage rating must be greater than the maximum input voltage. As a general rule, to

compensate the derating TI recommends a voltage rating of twice the maximum input voltage.

It is very important in buck regulator to place the small decoupling capacitor right next to the PVIN and PGND

pins. This capacitor is used to bypass the high frequency switching noise by providing a return path of the noise.

It prevents the noise from spreading to wider area of the board. The large bypass ceramic capacitor must also

be as close as possible to the PVIN and PGND pins.

Additionally, some bulk capacitance can be required, especially if the LM73605-Q1/6-Q1 circuit is not located

within approximately two inches from the input voltage source. This capacitor is used to provide damping to the

voltage spike due to the lead inductance of the cable. The optimum value for this capacitor is four times the

ceramic input capacitance with ESR close to the characteristic impedance of the LC filter formed by your input

inductance and your ceramic input capacitors. It is not critical that the electrolytic filter be at the optimum value

for damping, but it must be rated to handle the maximum input voltage including ripple voltage.

For this design, two 10-µF, X7R dielectric capacitors rated for 50 V are used for the input decoupling

capacitance, and a capacitor with a value of 0.47 µF for high-frequency filtering.

Note

DC bias effect: High capacitance ceramic capacitors have a DC bias derating effect, which have

a strong influence on the final effective capacitance. Therefore, the right capacitor value has to

be chosen carefully. Package size and voltage rating in combination with dielectric material are

responsible for differences between the rated capacitor value and the effective capacitance.

9.2.2.5 Inductor Selection

The first criterion for selecting an output inductor is the inductance. In most buck converters, this value is based

on the desired peak-to-peak ripple current in the inductor, I_Lripple. An inductance that gives a ripple current of

10% to 30% of the maximum output current (5 A or 6 A) is a good starting point. The inductance can be

calculated from Equation 26:

V

_IN- V_OUTìD

(

)

L =

ƒ_SWìI_Lripple

(26)

where

•

I_Lripple= (0.1 to 0.3) × I_{L_MAX}

I_{L_MAX}= 5 A for LM73605-Q1 and 6 A for LM73606-Q1

D = V_OUT/ V_IN

The selected I_Lrippleis between 10% to 30% of the rated current of the device.

As with switching frequency, the selection of the inductor is a tradeoff between size, cost, and performance.

Higher inductance gives lower ripple current and hence lower output voltage ripple. With peak current mode

control, the current ripple is the input signal to the control loop. A certain amount of ripple current is needed

to maintain the signal-to-noise ratio of the control loop. Within the same series (same size/height), a larger

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inductance has a higher series resistance (ESR). With similar ESR, size, height, or both are greater. Larger

inductance also has slower current slew rate during large load transients.

Lower inductance usually results in a smaller, less expensive component; however, the current ripple will be

higher, thus more output capacitor is needed to maintain the same amount of output voltage ripple. The RMS

current is higher with the same load current due to larger ripple. The switching loss is higher because the switch

current, which is the peak current, is higher when the HS switch turns off and LS switch turns on. Core loss of

the inductor is also larger with higher ripple. Core loss needs to be considered, especially with higher switching

frequencies. Check the ripple current over V_{IN_MIN}to V_{IN_MAX}range to make sure current ripple is reasonable

over entire supply voltage range.

For applications with large V_OUTand typical V_OUT/ V_IN> 50%, subharmonic oscillation can be a concern in peak

current-mode-controlled buck converters. Select inductance so that:

L ≥ V_OUT/ (N × f_SW

)

(27)

where

•

N = 3 with LM73605-Q1

N = 3.6 with LM73606-Q1

The second criterion is inductor saturation current rating. Because the maximum inductor current is limited by the

high-side switch current limit, it is advised to select an inductor with a saturation current higher than the I_LIMIT-HS

.

TI recommends selection of soft saturation inductors. A power inductor can be the major source of radiated

noise. When EMI is a concern in the application, select a shielded inductor, if possible.

For this design, 20% ripple of 5 A yields 5.8-µH inductance. A 4.7-µH inductor is selected, which gives 25%

ripple current.

9.2.2.6 Output Capacitor Selection

The output capacitor is responsible for filtering the inductor current, and supplying load current during transients.

Capacitor selection depends on application conditions as well as ripple and transient requirements. Best

performance is achieved by using ceramic capacitors or combinations of ceramic and other types of capacitors.

For high output voltage conditions, such as 12 V and above, finding ceramic capacitors that are rated for

an appropriate voltage becomes challenging. In such cases, choose a low-ESR SP-CAP^™or POSCAP^™-type

capacitor. It is a good idea to use a low-value ceramic capacitor in parallel with other capacitors, to bypass high

frequency noise between ground and V_OUT

.

For a given input and output requirement, Equation 28 gives an approximation for a minimum output capacitor

required.

2

»

…

ÿ

Ÿ

≈

’

1

r

Å

C_OUT

>

ì

ì(1+ D ) + D ì(1+ r)

∆

÷

(

)

÷

(f_SWìr ì DV_OUT/ I_OUT

)

12

Ÿ

⁄

«

◊

(28)

where

•

r = Ripple ratio of the inductor ripple current (I_Lripple/ 5 A or 6 A)

ΔV_OUT= Target output voltage undershoot, for example, 5% to 10% of V_OUT

D’ = 1 – duty cycle

f_SW= Switching frequency

I_OUT= Load current

Along with Equation 28, for the same requirement calculate the maximum ESR with Equation 29.

Å

D

1

ESR <

ì( + 0.5)

f_SWìC_OUT

r

(29)

The output capacitor is also the dominating factor in the loop response of a peak-current mode controlled buck

converter. A simplified estimation of the control loop crossover frequency can be found by Equation 18.

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Select C_OUTso that the f_Xis no higher than 1/6 of the switching frequency. Typically, f_X/ f_SW= 1/10 to 1/8

provides a good combination of stability and performance.

For this design, one 0.47-µF, 50-V X7R and four 22-µF, 16-V, X7R ceramic capacitors are used in parallel.

9.2.2.7 Feedforward Capacitor

The LM73605-Q1/6-Q1 internally compensated. Typically, select R_FBT≤ 100 kΩ, then C_FFis not needed. When

very low quiescent current is needed, R_FBT= 1 MΩ can be used. If C_OUTis mainly ceramic type low ESR

capacitors, an external feedforward capacitor, C_FF, can be needed to improve the phase margin. Add C_FFin

parallel with R_FBT. C_FFis chosen such that the phase boost is maximized at the estimated crossover frequency

f_X. Equation 21 was tested.

With this design, because R_FBT= 100 kΩ is selected, no C_FFis needed.

9.2.2.8 Bootstrap Capacitors

Every LM73605-Q1/6-Q1 design requires a bootstrap capacitor, C_BOOT. The recommended bootstrap capacitor

is 0.47 µF and rated at 6.3 V or greater. The bootstrap capacitor is located between the SW pin and the

CBOOT pin. The bootstrap capacitor must be a high-quality ceramic type with X7R or X5R grade dielectric for

temperature stability.

9.2.2.9 VCC Capacitor

The VCC pin is the output of an internal LDO for the LM73605-Q1/6-Q1. The input for this LDO comes from

either V_INor BIAS pin voltage. The recommended C_VCCcapacitor is 2.2 µF and rated at 6.3 V or greater. It must

be a high-quality ceramic type with X7R or X5R grade to insure stability. Never short VCC pin to ground during

operation.

9.2.2.10 BIAS

Because V_OUT= 5 V in this design, the BIAS pin is tied to V_OUTto reduce LDO power loss. The output voltage

is supplying the LDO current instead of the input voltage. The power saving is I_LDO× (V_IN– V_OUT). The power

saving is more significant when V_IN>> V_OUTand with higher frequency operation. To prevent V_OUTnoise and

transients from coupling to BIAS, a series resistor, 1 Ω to 10 Ω, can be added between V_OUTand BIAS. A

bypass capacitor with a value of 1 μF or higher can be added close to the BIAS pin to filter noise.

9.2.2.11 Soft Start

The SS/TRK pin can be floating to start up following the internal soft-start ramp. In order to extend the soft-start

time, an external soft-start capacitor can be used. Use Equation 12 to calculate the soft-start capacitor value.

With a desired soft-start time t_SS= 11 ms, a soft-start charging current of I_SSC= 2 µA (typical), and V_FB= 1.006 V

(typical), Equation 12 yields a soft-start capacitor value of 22 nF.

9.2.2.12 Undervoltage Lockout Setpoint

The system undervoltage lockout (UVLO) is adjusted using the external voltage divider network of R_ENTand

R_ENB. With one selected R_ENTvalue, R_ENBcan be found by Equation 10.

Note that the divider adds to supply quiescent current by V_IN/ (R_ENT+ R_ENB). Small R_ENTand R_ENBvalues add

more quiescent current loss. However, large divider values make the node more sensitive to noise.

In this design, EN pin is tied to PVIN pin with a 100-kΩ resistor.

9.2.2.13 PGOOD

For this design, a 100-kΩ resistor is used to pull up PGOOD to V_OUT

.

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9.2.3 Application Curves

100

95

90

85

80

75

70

65

60

55

50

100

95

90

85

80

75

70

65

60

55

50

VIN = 5 V

VIN = 8 V

VIN = 12 V

VIN = 13.5 V

VIN = 18 V

VIN = 5 V

VIN = 8 V

VIN = 12 V

VIN = 13.5 V

VIN = 18 V

0.001

0.01 0.02 0.05 0.1 0.2 0.5

Load Current (A)

1

2

3 456

0

0.6 1.2 1.8 2.4

3

Load Current (A)

3.6 4.2 4.8 5.4

6

EFF_

V_OUT= 3.3 V

f_SW= 400 kHz

Auto Mode

V_OUT= 3.3 V

f_SW= 400 kHz

FPWM Mode

Figure 9-3. LM73606-Q1 Efficiency

Figure 9-4. LM73606-Q1 Efficiency

100

95

90

85

80

75

70

65

60

55

50

100

95

90

85

80

75

70

65

60

55

50

VIN = 5 V

VIN = 8V

VIN = 12 V

VIN = 5 V

VIN = 8V

VIN = 12 V

0.001

0.01 0.02 0.05 0.1 0.2

Load Current (A)

0.5

1

2

3 45

0

0.5

1

1.5

2

2.5

Load Current (A)

3

3.5

4

4.5

5

EFF_

V_OUT= 3.3 V

f_SW= 500 kHz

Auto Mode

V_OUT= 3.3 V

f_SW= 500 kHz

FPWM Mode

Figure 9-5. LM73605-Q1 Efficiency

Figure 9-6. LM73605-Q1 Efficiency

100

95

90

85

80

75

70

65

60

55

50

100

95

90

85

80

75

70

65

60

55

50

VIN = 5 V

VIN = 8V

VIN = 12 V

VIN = 5 V

VIN = 8V

VIN = 12 V

0.001

0.01 0.02 0.05 0.1 0.2

Load Current (A)

0.5

1

2

3 45

0

0.5

1

1.5

2

2.5

Load Current (A)

3

3.5

4

4.5

5

EFF_

V_OUT= 3.3 V

f_SW= 2200 kHz

Auto Mode

V_OUT= 3.3 V

f_SW= 2200 kHz

FPWM Mode

Figure 9-7. LM73605-Q1 Efficiency

Figure 9-8. LM73605-Q1 Efficiency

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100

95

90

85

80

75

70

65

60

55

50

100

95

90

85

80

75

70

65

60

55

50

VIN = 5 V

VIN = 8V

VIN = 12 V

VIN = 5 V

VIN = 8V

VIN = 12 V

0.001

0.01 0.02 0.05 0.1 0.2

Load Current (A)

0.5

1

2

3 45

0.001

0.01 0.02 0.05 0.1 0.2

Load Current (A)

0.5

1

2 3 45

EFF_

V_OUT= 3.3 V

f_SW= 350 kHz

Auto Mode

V_OUT= 3.3 V

f_SW= 1000 kHz

Auto Mode

Figure 9-9. LM73605-Q1 Efficiency

Figure 9-10. LM73605-Q1 Efficiency

100

95

90

85

80

75

70

65

60

55

50

100

95

90

85

80

75

70

65

60

55

50

VIN = 8 V

VIN = 12 V

VIN = 13.5 V

VIN = 18 V

VIN = 12 V

VIN = 13.5 V

VIN = 18 V

0.001

0.01 0.02 0.05 0.1 0.2 0.5

Load Current (A)

1

2

3 456

0

0.6 1.2 1.8 2.4

3

Load Current (A)

3.6 4.2 4.8 5.4

6

EFF_

V_OUT= 5 V

f_SW= 400 kHz

Auto Mode

V_OUT= 5 V

f_SW= 400 kHz

FPWM Mode

Figure 9-11. LM73606-Q1 Efficiency

Figure 9-12. LM73606-Q1 Efficiency

100

95

90

85

80

75

70

65

60

55

50

100

95

90

85

80

75

70

65

60

55

50

VIN = 7 V

VIN = 12 V

VIN = 24 V

VIN = 36 V

VIN = 12 V

VIN = 24 V

VIN = 36 V

0.001

0.01 0.02 0.05 0.1 0.2 0.5

Load Current (A)

1

2

3 456

0

0.6 1.2 1.8 2.4

3

Load Current (A)

3.6 4.2 4.8 5.4

6

EFF_

V_OUT= 5 V

f_SW= 500 kHz

Auto Mode

V_OUT= 5 V

f_SW= 500 kHz

FPWM Mode

Figure 9-13. LM73606-Q1 Efficiency

Figure 9-14. LM73606-Q1 Efficiency

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100

95

90

85

80

75

70

65

60

55

50

100

95

90

85

80

75

70

65

60

55

50

VIN = 7 V

VIN = 12 V

VIN = 24 V

VIN = 7 V

VIN = 12 V

VIN = 24 V

0.001

0.01 0.02 0.05 0.1 0.2 0.5

Load Current (A)

1

2

3 456

0

0.6 1.2 1.8 2.4

3

Load Current (A)

3.6 4.2 4.8 5.4

6

EFF_

V_OUT= 5 V

f_SW= 1000 kHz

Auto Mode

V_OUT= 5 V

f_SW= 1000 kHz

FPWM Mode

Figure 9-15. LM73606-Q1 Efficiency

Figure 9-16. LM73606-Q1 Efficiency

100

95

90

85

80

75

70

65

60

55

50

100

95

90

85

80

75

70

65

60

55

50

VIN = 7 V

VIN = 12 V

VIN = 24 V

VIN = 7 V

VIN = 12 V

VIN = 24 V

0.001

0.01 0.02 0.05 0.1 0.2 0.5

Load Current (A)

1

2

3 456

0

0.6 1.2 1.8 2.4

3

Load Current (A)

3.6 4.2 4.8 5.4

6

EFF_

V_OUT= 5 V

f_SW= 2200 kHz

Auto Mode

V_OUT= 5 V

f_SW= 2200 kHz

FPWM Mode

Figure 9-17. LM73606-Q1 Efficiency

Figure 9-18. LM73606-Q1 Efficiency

100

95

90

85

80

75

70

65

60

55

50

100

95

90

85

80

75

70

65

60

55

50

VIN = 14 V

VIN = 24V

VIN = 36 V

VIN = 14 V

VIN = 24V

VIN = 36 V

0.001

0.01 0.02 0.05 0.1 0.2

Load Current (A)

0.5

1

2

3 45

0

0.5

1

1.5

2

2.5

Load Current (A)

3

3.5

4

4.5

5

EFF_

V_OUT= 12 V

f_SW= 500 kHz

Auto Mode

V_OUT= 12 V

f_SW= 500 kHz

FPWM Mode

Figure 9-19. LM73605-Q1 Efficiency

Figure 9-20. LM73605-Q1 Efficiency

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5.2

5.16

5.12

5.08

5.04

5

5.05

5.04

5.03

5.02

5.01

5

VIN = 8 V

VIN = 12 V

VIN = 13.5 V

VIN = 18 V

4.99

4.98

4.97

4.96

4.95

4.96

4.92

4.88

4.84

4.8

VIN = 8 V

VIN = 12 V

VIN = 13.5 V

VIN = 18 V

0

0.6 1.2 1.8 2.4

3

Load Current (A)

3.6 4.2 4.8 5.4

6

0.001

0.01 0.02 0.05 0.1 0.2 0.5

Load Current (A)

1

2 3 456

REG_

V_OUT= 5 V

f_SW= 400 kHz

FPWM Mode

V_OUT= 5 V

f_SW= 400 kHz

Auto Mode

Figure 9-22. LM73606-Q1 Load and Line Regulation

Figure 9-21. LM73606-Q1 Load and Line Regulation

5.2

5.16

5.12

5.08

5.04

5

5.1

5.08

5.06

5.04

5.02

5

4.96

4.98

4.92

4.88

4.84

4.8

VIN = 7 V

VIN = 12 V

VIN = 24 V

VIN = 36 V

4.96

4.94

4.92

4.9

VIN = 7 V

VIN = 12 V

VIN = 24 V

VIN = 36 V

0.001

0.010.02 0.05 0.1 0.2 0.5

Load Current (A)

1

2

3 45 7 10

0

0.6 1.2 1.8 2.4

3

Load Current (A)

3.6 4.2 4.8 5.4

6

REG_

V_OUT= 5 V

f_SW= 500 kHz

Auto Mode

V_OUT= 5 V

f_SW= 500 kHz

FPWM Mode

Figure 9-23. LM73606-Q1 Load and Line Regulation Figure 9-24. LM73606-Q1 Load and Line Regulation

5.2

5.16

5.12

5.08

5.04

5

5.05

5.04

5.03

5.02

5.01

5

4.99

4.98

4.97

4.96

4.95

4.96

4.92

4.88

4.84

4.8

VIN = 7 V

VIN = 12 V

VIN = 24 V

VIN = 7 V

VIN = 12 V

VIN = 24 V

0

0.5

1

1.5

2

2.5

3

Load Current (A)

3.5

4

4.5

5

0.001

0.01 0.02 0.05 0.1 0.2

Load Current (A)

0.5

1

2 3 45

REG_

V_OUT= 5 V

f_SW= 2200 kHz

FPWM Mode

V_OUT= 5 V

f_SW= 2200 kHz

Auto Mode

Figure 9-26. LM73605-Q1 Load and Line Regulation

Figure 9-25. LM73605-Q1 Load and Line Regulation

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3.4

3.38

3.36

3.34

3.32

3.3

3.35

3.34

3.33

3.32

3.31

3.3

VIN = 5 V

VIN = 8 V

VIN = 12 V

VIN = 13.5 V

VIN = 18 V

3.28

3.29

3.28

3.27

3.26

3.25

VIN = 5 V

VIN = 8 V

VIN = 12 V

VIN = 13.5 V

VIN = 18 V

3.26

3.24

3.22

3.2

0.001

0.01 0.02 0.05 0.1 0.2 0.5

Load Current (A)

1

2

3 456

0

0.6 1.2 1.8 2.4

3

Load Current (A)

3.6 4.2 4.8 5.4

6

REG_

V_OUT= 3.3 V

f_SW= 400 kHz

Auto Mode

V_OUT= 3.3 V

f_SW= 400 kHz

FPWM Mode

Figure 9-27. LM73606-Q1 Load and Line Regulation Figure 9-28. LM73606-Q1 Load and Line Regulation

3.4

3.38

3.36

3.34

3.32

3.3

3.32

3.315

3.31

3.305

3.3

3.295

3.29

3.28

3.26

3.24

3.22

3.2

3.285

3.28

VIN = 5 V

VIN = 8V

VIN = 12 V

VIN = 5 V

VIN = 8V

VIN = 12 V

3.275

3.27

0.001

0.01 0.02 0.05 0.1 0.2

Load Current (A)

0.5

1

2 3 45

0.001

0.01 0.02 0.05 0.1 0.2

Load Current (A)

0.5

1

2 3 45

REG_

V_OUT= 3.3 V

f_SW= 2200 kHz

FPWM Mode

V_OUT= 3.3 V

f_SW= 2200 kHz

Auto Mode

Figure 9-30. LM73605-Q1 Load and Line Regulation

Figure 9-29. LM73605-Q1 Load and Line Regulation

3.4

3.38

3.36

3.34

3.32

3.3

3.4

3.38

3.36

3.34

3.32

3.3

3.28

3.26

VIN = 5 V

VIN = 8V

VIN = 12 V

VIN = 5 V

VIN = 8V

VIN = 12 V

3.24

3.22

3.2

3.24

3.22

3.2

0.001

0.01 0.02 0.05 0.1 0.2

Load Current (A)

0.5

1

2

3 45

0.001

0.01 0.02 0.05 0.1 0.2

Load Current (A)

0.5

1

2 3 45

REG_

V_OUT= 3.3 V

f_SW= 500 kHz

Auto Mode

V_OUT= 3.3 V

f_SW= 1000 kHz

Auto Mode

Figure 9-31. LM73605-Q1 Load and Line Regulation Figure 9-32. LM73605-Q1 Load and Line Regulation

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12.4

12.36

12.32

12.28

12.24

12.2

12.1

12.08

12.06

12.04

12.02

12

12.16

12.12

12.08

12.04

12

11.98

11.96

11.94

11.92

11.9

11.96

11.92

11.88

11.84

11.8

VIN = 14 V

VIN = 24V

VIN = 36 V

VIN = 14 V

VIN = 24V

VIN = 36 V

0.001

0.01 0.02 0.05 0.1 0.2

Load Current (A)

0.5

1

2

3 45

0.001

0.01 0.02 0.05 0.1 0.2

Load Current (A)

0.5

1

2 3 45

REG_

V_OUT= 12 V

f_SW= 500 kHz

Auto Mode

V_OUT= 12 V

f_SW= 500 kHz

FPWM Mode

Figure 9-33. LM73605-Q1 Load and Line Regulation Figure 9-34. LM73605-Q1 Load and Line Regulation

6

5.8

5.6

5.4

5.2

5

6

5.8

5.6

5.4

5.2

5

4.8

4.6

4.4

4.2

4

4.8

4.6

4.4

4.2

4

Load = 1.5 mA

Load = 1.5 A

Load = 3 A

Load = 1.5 mA

Load = 1.5 A

Load = 3 A

3.8

3.6

3.4

3.2

3.8

3.6

3.4

3.2

Load = 6 A

4

4.4

4.8

5.2

5.6

VIN (V)

6

6.4

6.8

4

4.4

4.8

5.2

5.6

VIN (V)

6

6.4

6.8

DO_5

V_OUT= 5 V

f_SW= 400 kHz

Auto Mode

V_OUT= 5 V

f_SW= 400 kHz

FPWM Mode

Figure 9-35. LM73606-Q1 Dropout Curve

Figure 9-36. LM73606-Q1 Dropout Curve

6

5.8

5.6

5.4

5.2

5

5.6

5.4

5.2

5

4.8

4.6

4.4

4.2

4

4.8

4.6

4.4

4.2

4

Load = 1.5mA

Load = 1A

Load = 3A

Load = 5A

Load = 1.5mA

Load = 1A

Load = 3A

Load = 5A

3.8

3.6

3.4

3.2

3.8

3.6

3.4

3.2

4

4.4

4.8

5.2

5.6

VIN (V)

6

6.4

6.8

4

4.4

4.8

5.2

5.6

VIN (V)

6

6.4

6.8

DO_5

V_OUT= 5 V

f_SW= 2200 kHz

Auto Mode

V_OUT= 5 V

f_SW= 2200 kHz

FPWM Mode

Figure 9-37. LM73605-Q1 Dropout Curve

Figure 9-38. LM73605-Q1 Dropout Curve

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6

5.8

5.6

5.4

5.2

5

6

5.8

5.6

5.4

5.2

5

4.8

4.6

4.4

4.2

4

4.8

4.6

4.4

4.2

4

Load = 1.5mA

Load = 1A

Load = 3A

Load = 5A

Load = 1.5mA

Load = 1A

Load = 3A

Load = 5A

3.8

3.6

3.4

3.2

3.8

3.6

3.4

3.2

4

4.4

4.8

5.2

5.6

VIN (V)

6

6.4

6.8

4

4.4

4.8

5.2

5.6

VIN (V)

6

6.4

6.8

DO_5

V_OUT= 5 V

f_SW= 500 kHz

Auto Mode

V_OUT= 5 V

f_SW= 1000 kHz

Auto Mode

Figure 9-39. LM73605-Q1 Dropout Curve

Figure 9-40. LM73605-Q1 Dropout Curve

3.5

3.4

3.3

3.2

3.1

3

3.4

3.3

3.2

3.1

3

2.9

2.8

2.7

2.6

2.5

2.9

2.8

2.7

2.6

2.5

Load = 1.5 mA

Load = 1.5 A

Load = 3 A

Load = 1.5 mA

Load = 1.5 A

Load = 3 A

Load = 6 A

3.5

4

4.5

5

5.5

VIN (V)

6

6.5

7

3.5

4

4.5

5

5.5

VIN (V)

6

6.5

7

DO_3

V_OUT= 3.3 V

f_SW= 400 kHz

Auto Mode

V_OUT= 3.3 V

f_SW= 400 kHz

FPWM Mode

Figure 9-41. LM73606-Q1 Dropout Curve

Figure 9-42. LM73606-Q1 Dropout Curve

3.5

13

12.8

3.4

3.3

3.2

3.1

3

12.6

12.4

12.2

12

11.8

11.6

11.4

11.2

11

2.9

2.8

2.7

2.6

2.5

Load = 1.5mA

Load = 1A

Load = 3A

Load = 5A

Load = 1.5mA

Load = 1A

Load = 3A

Load = 5A

10.8

10.6

10.4

10.2

10

11

11.4

11.8

12.2

12.6

VIN (V)

13

13.4

13.8

3.3

3.5

3.7

3.9

4.1

VIN (V)

4.3

4.5

4.7

4.9

DO_1

DO_3

V_OUT= 12 V

f_SW= 500 kHz

Auto Mode

V_OUT= 3.3 V

f_SW= 500 kHz

Auto Mode

Figure 9-44. LM73605-Q1 Dropout Curve

Figure 9-43. LM73605-Q1 Dropout Curve

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I_INDUCTOR

(1 A/DIV)

V_OUTRipple

(20 mV/DIV)

V_OUTRipple

(20 mV/DIV)

V_SW

(5 V/DIV)

Time (500 µs/DIV)

Time (2 µs/DIV)

V_IN= 12 V

I_OUT= 1 mA

V_OUT= 3.3 V

Auto Mode

f_SW= 500 kHz

V_IN= 12 V

I_OUT= 1 mA

V_OUT= 3.3 V

FPWM Mode

f_SW= 500 kHz

Figure 9-45. LM73606-Q1 Switching Waveform and Figure 9-46. LM73606-Q1 Switching Waveform and

V_OUTRipple

I_INDUCTOR

(1 A/DIV)

V_OUTRipple

(20 mV/DIV)

V_OUTRipple

(20 mV/DIV)

V_SW

(5 V/DIV)

V_SW

(5 V/DIV)

Time (5 µs/DIV)

V_IN= 12 V

I_OUT= 100 mA

V_OUT= 3.3 V

Auto Mode

f_SW= 500 kHz

V_IN= 12 V

I_OUT= 100 mA

V_OUT= 3.3 V

FPWM Mode

f_SW= 500 kHz

Figure 9-47. LM73606-Q1 Switching Waveform and Figure 9-48. LM73606-Q1 Switching Waveform and

V_OUTRipple

I_INDUCTOR

(2 A/DIV)

(1 A/DIV)

V_OUTRipple

(20 mV/DIV)

V_OUTRipple

(20 mV/DIV)

V_SW

(5 V/DIV)

Time (2 µs/DIV)

Time (5 µs/DIV)

V_IN= 12 V

I_OUT= 6 A

V_OUT= 3.3 V

Auto Mode

f_SW= 500 kHz

V_IN= 3.66 V

I_OUT= 3 A

V_OUT= 3.3 V

Auto Mode

f_SWset at 500 kHz

Figure 9-49. LM73606-Q1 Switching Waveform and Figure 9-50. LM73606-Q1 Switching Waveform at

V_OUTRipple

Dropout

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I_INDUCTOR

(2 A/DIV)

V_OUT

(1 V/DIV)

V_OUT

(1 V/DIV)

I_INDUCTOR

(2 A/DIV)

V_SW

(5 V/DIV)

V_SW

(5 V/DIV)

Time (5 µs/DIV)

Time (50 ms/DIV)

V_IN= 12 V

V_OUTset at 3.3 V

f_SWset at 500 kHz

V_IN= 12 V

V_OUT= 3.3 V

f_SW= 500 kHz

I_OUT= 7.5 A

V_OUTdroops to 2 V

Figure 9-52. LM73606-Q1 Short-Circuit Hiccup

Protection and Recovery

Figure 9-51. LM73606-Q1 Overcurrent Behavior

Enable

(5 V/DIV)

Enable

(5 V/DIV)

V_OUT

(2 V/DIV)

V_OUT

(2 V/DIV)

I_INDUCTOR

(2 A/DIV)

PGOOD

(10 V/DIV)

Time (2 ms/DIV)

V_IN= 12 V

V_OUT= 3.3 V

FPWM Mode

f_SW= 500 kHz

V_IN= 12 V

V_OUT= 3.3 V

Auto Mode

f_SW= 500 kHz

I_OUT= 200 mA

Figure 9-53. LM73606-Q1 Soft Start With 200-mA

Load in FPWM Mode

Figure 9-54. LM73606-Q1 Soft Start With 200-mA

Load in Auto Mode

Enable

(5 V/DIV)

Enable

(5 V/DIV)

V_OUT

(2 V/DIV)

V_OUT

(2 V/DIV)

I_INDUCTOR

(2 A/DIV)

PGOOD

(5 V/DIV)

Time (2 ms/DIV)

V_IN= 12 V

I_OUT= 5 A

V_OUT= 3.3 V

Auto Mode

f_SW= 500 kHz

V_IN= 12 V

V_OUT= 3.3 V

Auto Mode

f_SW= 500 kHz

V_PRE-BIAS= 1.5 V

Figure 9-55. LM73606-Q1 Soft Start With 5-A Load

Figure 9-56. LM73606-Q1 Soft Start With Pre-

Biased Output Voltage

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I_OUT

(5 A/DIV)

I_INDUCTOR

(5 A/DIV)

V_OUT

(200 mV/

DIV AC)

V_OUT

(200 mV/

DIV AC)

Time (200 µs/DIV)

V_IN= 12 V

V_OUT= 3.3 V

f_SW= 500 kHz

Auto Mode

V_IN= 12 V

V_OUT= 3.3 V

f_SW= 500 kHz

FPWM Mode

I_OUT= 10 mA to 6 A to 10 mA

Figure 9-57. LM73606-Q1 Load Transients

Figure 9-58. LM73606-Q1 Load Transients

I_OUT

(5 A/DIV)

I_INDUCTOR

(5 A/DIV)

V_OUT

(500 mV/

DIV AC)

(500 mV/

DIV AC)

Time (200 µs/DIV)

V_IN= 12 V

V_OUT= 5 V

f_SW= 2200 kHz

Auto Mode

V_IN= 12 V

V_OUT= 5 V

f_SW= 2200 kHz

FPWM Mode

I_OUT= 10 mA to 5 A to 10 mA

Figure 9-59. LM73605-Q1 Load Transients

Figure 9-60. LM73605-Q1 Load Transients

V_IN

(20 V/DIV)

V_OUT

(200 mV/

DIV)

(200 mV/

DIV)

I_INDUCTOR

(2 A/DIV)

Time (200 µs/DIV)

I_OUT= 100 mA

V_OUT= 3.3 V

f_SW= 500 kHz

Auto Mode

I_OUT= 2 A

V_OUT= 3.3 V

f_SW= 500 kHz

Auto Mode

V_IN= 10 V to 35 V to 10 V

Figure 9-61. LM73606-Q1 Line Transients

Figure 9-62. LM73606-Q1 Line Transients

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I_INDUCTOR

LW_PK5

(1 A/DIV)

VHF1-PK5

VHF1-AV5

MW_PK5

MW_AV5

VHF2-PK5 FM-PK5

SW_PK5

SW_AV5

LW_AV5

V_OUTRipple

TVI-PK5

TVI-AV5

(20 mV/DIV)

CB_PK5

CB_AV5

V_SW

(5 V/DIV)

VHF2-AV5 FM-AV5

Time (500 µs/DIV)

Peak Value

Average Value

Peak Value

Average Value

V_IN= 12 V

f_SW= 400 kHz

C_FLT= 4 × 4.7 µF

V_OUT= 5 V

I_OUT= 4 A

V_IN= 12 V

f_SW= 400 kHz

C_FLT= 4 × 4.7 µF

V_OUT= 5 V

Tested on LM73606EVM-5V-400k

L_IN= 1 µH C_BULK= 10 µF

I_OUT= 4 A

Tested on LM73606EVM-5V-400k

L_IN= 1 µH C_BULK= 10 µF

Figure 9-64. LM73606-Q1 Conducted EMI Result

versus CISPR25 Limits - High Frequency

Figure 9-63. LM73606-Q1 Conducted EMI Result

versus CISPR25 Limits - Low Frequency

LW_PK5

VHF1-PK5

MW_PK5

VHF2-PK5 FM-PK5

SW PK5

SW AV5

LW_AV5

TVI-PK5

CB_PK5

CB_AV5

MW_AV5

VHF1-AV5

TVI-AV5

VHF2-AV5 FM-AV5

Peak Value

Average Value

Peak Value

Average Value

V_IN= 13.5 V

f_SW= 2.2 MHz

C_FLT= 3 × 2.2 µF

V_OUT= 5 V

I_OUT= 3.5 A

V_IN= 13.5 V

f_SW= 2.2 MHz

C_FLT= 3 × 2.2 µF

V_OUT= 5 V

I_OUT= 3.5 A

Tested on LM73605EVM-5V-2MHZ

L_IN= 0.6 µH

C_BULK= 10 µF

C_CHOKE= 2 × 2.2

µF

L_IN= 0.6 µH

C_BULK= 10 µF

C_CHOKE= 2 × 2.2

µF

CM Choke = ACM1211-102-2PL-TL01

Figure 9-65. LM73606-Q1 Conducted EMI Result

versus CISPR25 Limits - Low Frequency

Figure 9-66. LM73606-Q1 Conducted EMI Result

versus CISPR25 Limits - High Frequency

50

Peak_Limit

45

Peak detector _Vertical_Log

45

AVG_Limit

Peak detector _Horizontal_Log

Peak detector _Vertical_Bicon

40

Peak detector _Horizontal_Bicon

40

35

30

25

20

15

10

30

25

20

15

10

5

0

200

300

400

500

600

700

800

900

1000

30

40

50

60

70

80

90

100

110

120

130

140

150

160

170

180

190

200

Frequency (MHz)

Frequency(MHz)

V_IN= 13.5 V

f_SW= 400 kHz

C_FLT= 3 × 2.2 µF

V_OUT= 5 V

Tested on LM73606EVM-5V-400k

L_IN= 1 µH C_BULK= 10 µF

I_OUT= 5 A

V_IN= 13.5 V

f_SW= 400 kHz

C_FLT= 3 × 2.2 µF

V_OUT= 5 V

Tested on LM73606EVM-5V-400k

L_IN= 1 µH C_BULK= 10 µF

I_OUT= 5 A

Figure 9-68. LM73606-Q1 Radiated EMI Result

versus CISPR25 Limits - High Frequency

Figure 9-67. LM73606-Q1 Radiated EMI Result

versus CISPR25 Limits - Low Frequency

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50

45

40

35

30

25

20

15

10

5

50

45

40

35

30

25

20

15

10

Peak_Limit

AVG_Limit

Peak detector _Vertical_Log

Peak detector _Horizontal_Log

Peak detector_Vertical_Bicon

Peak Detector_Horizontal_Bicon

0

30

50

70

90

110

130

150

170

190

200

300

400

500

600

700

800

900

1000

Frequency(MHz)

Frequency (MHz)

V_IN= 13.5 V

f_SW= 2200 kHz

C_FLT= 3 × 2.2 µF

V_OUT= 5 V

I_OUT= 3 A

V_IN= 13.5 V

f_SW= 2200 kHz

C_FLT= 3 × 2.2 µF

V_OUT= 5 V

Tested on LM73605EVM-5V-2MHZ

L_IN= 0.6 µH C_BULK= 10 µF

I_OUT= 3 A

Tested on LM73605EVM-5V-2MHZ

L_IN= 0.6 µH

C_BULK= 10 µF

C_CHOKE= 2 × 2.2

µF

CM Choke = ACM1211-102-2PL-TL01

C_CHOKE= 2 × 2.2

µF

Figure 9-69. LM73606-Q1 Radiated EMI Result

versus CISPR25 Limits - Low Frequency

Figure 9-70. LM73606-Q1 Radiated EMI Result

versus CISPR25 Limits - High Frequency

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Power Supply Recommendations

The LM73605-Q1/6-Q1 designed to operate from an input voltage supply range from 3.5 V to 36 V. This input

supply must be able to withstand the maximum input current and maintain a voltage above 3.5 V at the PVIN pin.

The resistance of the input supply rail must be low enough that an input current transient does not cause a high

enough drop at the LM73605-Q1/6-Q1 supply that can cause a false UVLO fault triggering and system reset. If

the input supply is located more than a few inches from the LM73605-Q1/6-Q1, additional bulk capacitance can

be required in addition to the ceramic bypass capacitors. A 47-μF or 100-μF electrolytic capacitor is a typical

choice.

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9 Layout

9.1 Layout Guidelines

The performance of any switching converter depends heavily upon the layout of the PCB. Use the following

guidelines to design a PCB layout with optimum power conversion performance, EMI performance, and thermal

performance.

1. Place ceramic high frequency bypass capacitors as close as possible to the PVIN and PGND pins, which are

right next to each other on the package. Place the small value ceramic capacitor closest to the pins. This is

very important for EMI performance.

2. Use short and wide traces, or localized IC layer planes, for high current paths, such as V_IN, V_OUT, SW, and

GND connections. Short and wide copper traces reduce power loss and noise due to low parasitic resistance

and inductance. Wide copper traces also help reduce die temperature, because they also provide wide heat

dissipation paths. Use thick copper (2 oz) on high current layer or layers if possible.

3. Confine pulsing current paths (V_IN, SW, and ground return for V_IN) on the device layer as much as possible

to prevent switching noises from contaminating other layers.

4. C_BOOTcapacitor also contains pulsing current. Place C_BOOTclose to the pin and route to SW with short

trace. The pinout of the device makes it easy to optimize the C_BOOTplacement and routing.

5. Use a solid ground plane at the layer right underneath the device as a noise shielding and heat dissipation

path.

6. Place the VCC bypass capacitor close to the VCC pin. Tie the ground pad of the capacitor to the ground

plane using a via right next to it.

7. Use via next to AGND pin to the ground plane.

8. Minimize trace length to the FB pin. Both feedback resistors must be located right next to the FB pin. Tie the

ground side of R_FBBto the ground plane with a via right next to it. Place C_FFdirectly in parallel with R_FBTif

used.

9. If V_OUTaccuracy at the load is important, make sure the V_OUTsense point is made close to the load. Route

V_OUTsense to R_FBTthrough a path away from noisy nodes and preferably on a layer on the other side of the

ground plane. If BIAS is connected to V_OUT, do not use the same trace to route V_OUTto BIAS and to R_FBT

.

BIAS current contains pulsing driver current and it changes with operating mode. Use separated traces for

BIAS and V_OUTsense to optimize V_OUTregulation accuracy.

10. Provide adequate device heat sinking. Use an array of heat-sinking vias to connect the exposed pad to the

ground plane and the bottom PCB layer. Connect the DAP and NC pins on the short sides of the device

to the GND net, so that IC layer ground copper can provide an optimal dog-bone shape heat sink. Heat

generated on the die can flow directly from device junction to the DAP then to the copper and spread to

the wider copper outside of the device. Try to keep copper area solid on the top and bottom layer around

thermal vias on the DAP to optimize heat dissipation.

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9.1.1 Layout For EMI Reduction

To optimize EMI performance, place the components in the high di/dt current path, as shown in Figure 9-1, as

close as possible to each other. When the components are close to each other, the area of the loop enclosed by

these components, and the parasitic inductance of this loop, are minimized. The noises generated by the pulsing

current and parasitic inductances are then minimized.

BUCK

CONVERTER

L

VIN

V_IN

C_IN

SW

V_OUT

C_OUT

PGND

High di/dt current

Figure 9-1. Pulsing Current Path of Buck Converter

In a buck converter, the high di/dt current path is composed of the HS and LS MOSFETs and the input

capacitors. Because the two MOSFETs are integrated inside the device, they are closer to each other than in

discrete solutions. PVIN and PGND pins are the connections from the MOSFETs to the input capacitors. The first

step of the layout must be placing the input capacitors, especially the small value ceramic bypass one, as close

as possible to PVIN and PGND pins.

The LM73605-Q1/6-Q1 pinout is optimized for low EMI layout. Multiple pins are used for PVIN and PGND to

minimized bond wire resistances and inductances. The PVIN and PGND pins are right next to each other to

simplify optimal layout. The CBOOT pin is placed next to SW pin for easy and compact C_BOOTcapacitor layout.

9.1.2 Ground Plane

The ground plane of a PCB provides the best return path for the pulsing current on the device layer. Make sure

the ground plane is solid, especially the part right underneath the pulsing current paths. Solid copper under a

pulsing current path provide a mirrored return path for the high frequency components and minimize voltage

spikes generated by the pulsing current. It shields the layers on the other side of the plane from switching

noises. Route signal traces on the other side of the ground plane as much as possible. Use multiple vias in

parallel to connect the grounds on the device layer to the ground plane.

9.1.3 Optimize Thermal Performance

The key to thermal optimization on PCB design is to provide heat transferring paths from the device to the outer

large copper area. Use thick copper (2 oz) on high current layer or layers if possible. Use thermal vias under the

DAP to transfer heat to other layers. Connect NC pins to the GND net, so that GND copper can run underneath

the device to create dog-bone shaped heat sink. Try to leave copper solid on IC side as much as possible above

and below the device. Place components and route traces away from major heat transferring paths if possible,

to avoid blocking heat dissipation path. Try to leave copper solid, free of components and traces, around the

thermal vias on the other side of the board as well. Solid copper behaves as heat sink to spread the heat to a

larger area and provide more contact area to the air.

When calculating power dissipation, use the maximum input voltage and the average output current for the

application. Many common operating conditions are provided in the Section 9.2.3. Less common applications

can be derived through interpolation. In all designs, the junction temperature must be kept below the rated

maximum of 125°C.

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The thermal characteristics of the LM73605-Q1/6-Q1 are specified using the parameter R_θJA, which characterize

thermal resistance from the junction of the silicon to the ambient in a specific system. Although the value of R_θJA

is dependant on many variables, it still can be used to approximate the operating junction temperature of the

device. To obtain an estimate of the device junction temperature, you can use Equation 30:

T_J= P_{IC_LOSS}× R_θJA+ T_A

(30)

where

•

T_J= Junction temperature in °C

P_{IC_LOSS}= V_IN× I_IN× (1 − efficiency) − 1.1 × I_OUT× DCR

DCR = Inductor DC parasitic resistance in Ω

R_θJA= Junction-to-ambient thermal resistance of the device in °C/W

T_A= Ambient temperature in °C.

The maximum operating junction temperature of the LM73605-Q1/6-Q1 is 125°C. R_θJAis highly related to PCB

size and layout, as well as environmental factors such as heat sinking and air flow. Figure 9-2 shows measured

results of R_θJAwith different copper area on 2-layer boards and 4-layer boards, with 1-W and 2-W power

dissipation on the LM73605-Q1/6-Q1.

30

1W @0 fpm - 2layer

28

1W @0 fpm - 4layer

26

2W @0 fpm - 2layer

2W @0 fpm - 4layer

24

22

20

18

16

14

12

10

20

30

30mm × 30mm

40

40mm × 40mm

50

50mm × 50mm

60

70

80

70mm ×70mm

Copper Area

Figure 9-2. Measured R_θJAversus PCB Copper Area on 2-Layer Boards and 4-Layer Boards

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9.2 Layout Example

A layout example is shown in Figure 9-3. A four-layer board is used with 2-oz copper on the top and bottom

layers and 1-oz copper on the inner two layers. Figure 9-3 shows the relative scale of the LM73605-Q1/6-Q1

with 0805 and 1210 input and output capacitors, 7-mm × 7-mm inductor and 0603 case size for all other passive

components. The trace width of the signal connections are not to scale.

The components are placed on the top layer and the high current paths are routed on the top layer as well. The

remaining space on the top layer can be filled with GND polygon. Thermal vias are used under the DAP and

around the device. The GND copper was extended to the outside of the device, which serves as copper heat

sink.

The mid-layer 1 is right underneath the top layer. It is a solid ground plane, which serves as noise shielding and

heat dissipation path.

The V_OUTsense trace is routed on the third layer, which is mid-layer 2. Ground plane provided noise shielding

for the sense trace. The V_OUTto BIAS connection is routed by a separate trace.

The bottom layer is also a solid ground copper in this example. Solid copper provides best heat sinking for the

device. If components and traces need to be on the bottom layer, leave the area around thermal vias as solid

as possible. Try not to cut heat dissipation path by a trace. The board can be used for various frequencies and

output voltages, with component variation. For more details, see the LM73605/LM73606 EVM User's Guide.

Figure 9-3. LM73605-Q1/6-Q1 Layout Example

50

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LM73605-Q1, LM73606-Q1

SNVSB12B – NOVEMBER 2017 – REVISED MAY 2021

www.ti.com

10 Device and Documentation Support

10.1 Device Support

10.1.1 Third-Party Products Disclaimer

TI'S PUBLICATION OF INFORMATION REGARDING THIRD-PARTY PRODUCTS OR SERVICES DOES NOT

CONSTITUTE AN ENDORSEMENT REGARDING THE SUITABILITY OF SUCH PRODUCTS OR SERVICES

OR A WARRANTY, REPRESENTATION OR ENDORSEMENT OF SUCH PRODUCTS OR SERVICES, EITHER

ALONE OR IN COMBINATION WITH ANY TI PRODUCT OR SERVICE.

10.1.2 Development Support

10.1.2.1 Custom Design With WEBENCH® Tools

Click here to create a custom design using the LM73605-Q1 or LM73606-Q1 device with the WEBENCH®

Power Designer.

1. Start by entering the input voltage (V_IN), output voltage (V_OUT), and output current (I_OUT) requirements.

2. Optimize the design for key parameters such as efficiency, footprint, and cost using the optimizer dial.

3. Compare the generated design with other possible solutions from Texas Instruments.

The WEBENCH Power Designer provides a customized schematic along with a list of materials with real-time

pricing and component availability.

In most cases, these actions are available:

•

Run electrical simulations to see important waveforms and circuit performance

Run thermal simulations to understand board thermal performance

Export customized schematic and layout into popular CAD formats

Print PDF reports for the design, and share the design with colleagues

Get more information about WEBENCH tools at www.ti.com/WEBENCH.

10.2 Documentation Support

10.2.1 Related Documentation

For related documentation see the following:

•

AN-2020 Thermal Design By Insight, Not Hindsight

10.3 Receiving Notification of Documentation Updates

To receive notification of documentation updates, navigate to the device product folder on ti.com. Click on

Subscribe to updates to register and receive a weekly digest of any product information that has changed. For

change details, review the revision history included in any revised document.

10.4 Receiving Notification of Documentation Updates

To receive notification of documentation updates, navigate to the device product folder on ti.com. In the upper

right corner, click on Alert me to register and receive a weekly digest of any product information that has

changed. For change details, review the revision history included in any revised document.

Submit Document Feedback

51

Product Folder Links: LM73605-Q1 LM73606-Q1

LM73605-Q1, LM73606-Q1

SNVSB12B – NOVEMBER 2017 – REVISED MAY 2021

www.ti.com

10.5 Support Resources

10.6 Support Resources

TI E2E^™support forums are an engineer's go-to source for fast, verified answers and design help — straight

from the experts. Search existing answers or ask your own question to get the quick design help you need.

Linked content is provided "AS IS" by the respective contributors. They do not constitute TI specifications and do

not necessarily reflect TI's views; see TI's Terms of Use.

10.7 Trademarks

SP-CAP^™is a trademark of Panasonic.

POSCAP^™is a trademark of Sanyo Electric Co., Ltd..

TI E2E^™is a trademark of Texas Instruments.

WEBENCH^®is a registered trademark of Texas Instruments.

All trademarks are the property of their respective owners.

10.8 Electrostatic Discharge Caution

This integrated circuit can be damaged by ESD. Texas Instruments recommends that all integrated circuits be handled

with appropriate precautions. Failure to observe proper handling and installation procedures can cause damage.

ESD damage can range from subtle performance degradation to complete device failure. Precision integrated circuits may

be more susceptible to damage because very small parametric changes could cause the device not to meet its published

specifications.

10.9 Glossary

TI Glossary

This glossary lists and explains terms, acronyms, and definitions.

52

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SNVSB12B – NOVEMBER 2017 – REVISED MAY 2021

www.ti.com

Mechanical, Packaging, and Orderable Information

The following pages include mechanical, packaging, and orderable information. This information is the most

current data available for the designated devices. This data is subject to change without notice and revision of

this document. For browser-based versions of this data sheet, refer to the left-hand navigation.

Submit Document Feedback

53

Product Folder Links: LM73605-Q1 LM73606-Q1

PACKAGE MATERIALS INFORMATION

www.ti.com

17-May-2021

TAPE AND REEL INFORMATION

*All dimensions are nominal

Device

Package Package Pins

Type Drawing

SPQ

Reel

A0

B0

K0

P1

W

Pin1

Diameter Width (mm) (mm) (mm) (mm) (mm) Quadrant

(mm) W1 (mm)

LM73605QRNPRQ1

LM73605QRNPTQ1

LM73605QURNPRQ1

LM73606QRNPRQ1

LM73606QRNPTQ1

LM73606QURNPRQ1

WQFN

RNP

30

3000

250

330.0

180.0

330.0

180.0

330.0

16.4

4.25

6.25

0.95

8.0

16.0

Q1

3000

250

3000

Pack Materials-Page 1

PACKAGE MATERIALS INFORMATION

www.ti.com

17-May-2021

*All dimensions are nominal

Device

Package Type Package Drawing Pins

SPQ

Length (mm) Width (mm) Height (mm)

LM73605QRNPRQ1

LM73605QRNPTQ1

LM73605QURNPRQ1

LM73606QRNPRQ1

LM73606QRNPTQ1

LM73606QURNPRQ1

WQFN

RNP

30

3000

250

367.0

213.0

367.0

213.0

367.0

191.0

367.0

191.0

367.0

38.0

35.0

38.0

35.0

38.0

3000

250

3000

Pack Materials-Page 2

GENERIC PACKAGE VIEW

RNP 30

4 x 6, 0.5 mm pitch

WQFN - 0.8 mm max height

PLASTIC QUAD FLATPACK - NO LEAD

This image is a representation of the package family, actual package may vary.

Refer to the product data sheet for package details.

4225831/A

www.ti.com

PACKAGE OUTLINE

RNP0030A

WQFN - 0.8 mm max height

S

C

A

L

E

2

.

7

0

PLASTIC QUAD FLATPACK - NO LEAD

4.1

3.9

B

A

PIN 1 INDEX AREA

6.1

5.9

0.1 MIN

(0.05)

E

SCAL

C

T

SECTION A-A

TYPICAL

0.8

0.7

C

SEATING PLANE

0.08

0.05

0.00

2.2 0.1

2X 1.5

(0.2) TYP

EXPOSED

THERMAL PAD

12

15

26X 0.5

11

16

SYMM

A

4.6 0.1

2X

5

1

26

0.3

PIN 1 ID

(OPTIONAL)

30

27

30X

0.2

0.1

0.05

SYMM

0.5

0.3

8X

C A B

0.65

0.45

22X

4222145/C 02/2018

NOTES:

1. All linear dimensions are in millimeters. Any dimensions in parenthesis are for reference only. Dimensioning and tolerancing

per ASME Y14.5M.

2. This drawing is subject to change without notice.

3. The package thermal pad must be soldered to the printed circuit board for thermal and mechanical performance.

www.ti.com

EXAMPLE BOARD LAYOUT

RNP0030A

WQFN - 0.8 mm max height

PLASTIC QUAD FLATPACK - NO LEAD

(2.2)

SYMM

8X (0.6)

30

27

22X (0.75)

1

26

30X (0.25)

2X

(2.05)

(0.5) TYP

SYMM

(5.8)

(4.6)

6X

(1.16)

(R0.05) TYP

16

11

(

0.2) TYP

VIA

12

15

6X (0.85)

(3.65)

LAND PATTERN EXAMPLE

SCALE:15X

0.07 MAX

ALL AROUND

0.07 MIN

ALL AROUND

SOLDER MASK

OPENING

METAL

SOLDER MASK

OPENING

METAL UNDER

SOLDER MASK

NON SOLDER MASK

SOLDER MASK

DEFINED

(PREFERRED)

SOLDER MASK DETAILS

4222145/C 02/2018

NOTES: (continued)

4. This package is designed to be soldered to a thermal pad on the board. For more information, see Texas Instruments literature

number SLUA271 (www.ti.com/lit/slua271).

www.ti.com

EXAMPLE STENCIL DESIGN

RNP0030A

WQFN - 0.8 mm max height

PLASTIC QUAD FLATPACK - NO LEAD

SYMM

(0.59) TYP

30

8X (0.6)

27

22X (0.75)

1

26

30X (0.25)

26X (0.5)

(1.16)

TYP

(0.58)

TYP

SYMM

(5.8)

METAL

TYP

8X (0.96)

16

11

(R0.05) TYP

12

15

8X (0.98)

(3.65)

SOLDER PASTE EXAMPLE

BASED ON 0.125 mm THICK STENCIL

EXPOSED PAD

74.4% PRINTED SOLDER COVERAGE BY AREA

SCALE:20X

4222145/C 02/2018

NOTES: (continued)

5. Laser cutting apertures with trapezoidal walls and rounded corners may offer better paste release. IPC-7525 may have alternate

design recommendations.

www.ti.com

PACKAGE OUTLINE

RNP0030C

WQFN - 0.8 mm max height

S

C

A

L

E

2

.

7

0

PLASTIC QUAD FLATPACK - NO LEAD

4.1

3.9

B

A

PIN 1 INDEX AREA

6.1

5.9

0.8

0.7

C

SEATING PLANE

0.08

0.05

0.00

2.2 0.1

2X 1.5

(0.2) TYP

EXPOSED

THERMAL PAD

12

15

26X 0.5

11

16

SYMM

4.6 0.1

2X

5

1

26

0.3

30X

PIN 1 ID

(OPTIONAL)

30

27

0.2

SYMM

0.5

0.3

0.1

C A B

8X

0.05

0.65

0.45

22X

4225790/A 03/2020

NOTES:

1. All linear dimensions are in millimeters. Any dimensions in parenthesis are for reference only. Dimensioning and tolerancing

per ASME Y14.5M.

2. This drawing is subject to change without notice.

3. The package thermal pad must be soldered to the printed circuit board for thermal and mechanical performance.

www.ti.com

EXAMPLE BOARD LAYOUT

RNP0030C

WQFN - 0.8 mm max height

PLASTIC QUAD FLATPACK - NO LEAD

(2.2)

SYMM

8X (0.6)

30

27

22X (0.75)

1

26

30X (0.25)

2X

(2.05)

(0.5) TYP

SYMM

(5.8)

(4.6)

6X

(1.16)

(R0.05) TYP

16

11

(

0.2) TYP

VIA

12

15

6X (0.85)

(3.65)

LAND PATTERN EXAMPLE

EXPOSED METAL SHOWN

SCALE:15X

0.07 MAX

ALL AROUND

0.07 MIN

ALL AROUND

SOLDER MASK

OPENING

METAL

EXPOSED

METAL

EXPOSED

METAL

SOLDER MASK

OPENING

METAL UNDER

SOLDER MASK

NON SOLDER MASK

SOLDER MASK

DEFINED

(PREFERRED)

SOLDER MASK DETAILS

4225790/A 03/2020

NOTES: (continued)

4. This package is designed to be soldered to a thermal pad on the board. For more information, see Texas Instruments literature

number SLUA271 (www.ti.com/lit/slua271).

www.ti.com

EXAMPLE STENCIL DESIGN

RNP0030C

WQFN - 0.8 mm max height

PLASTIC QUAD FLATPACK - NO LEAD

SYMM

(0.59) TYP

30

8X (0.6)

27

22X (0.75)

1

26

30X (0.25)

26X (0.5)

(1.16)

TYP

(0.58)

TYP

SYMM

(5.8)

METAL

TYP

8X (0.96)

16

11

(R0.05) TYP

12

15

8X (0.98)

(3.65)

SOLDER PASTE EXAMPLE

BASED ON 0.125 mm THICK STENCIL

EXPOSED PAD

74.4% PRINTED SOLDER COVERAGE BY AREA

SCALE:20X

4225790/A 03/2020

NOTES: (continued)

5. Laser cutting apertures with trapezoidal walls and rounded corners may offer better paste release. IPC-7525 may have alternate

design recommendations.

www.ti.com

IMPORTANT NOTICE AND DISCLAIMER

TI PROVIDES TECHNICAL AND RELIABILITY DATA (INCLUDING DATASHEETS), DESIGN RESOURCES (INCLUDING REFERENCE

DESIGNS), APPLICATION OR OTHER DESIGN ADVICE, WEB TOOLS, SAFETY INFORMATION, AND OTHER RESOURCES “AS IS”

AND WITH ALL FAULTS, AND DISCLAIMS ALL WARRANTIES, EXPRESS AND IMPLIED, INCLUDING WITHOUT LIMITATION ANY

IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE OR NON-INFRINGEMENT OF THIRD

PARTY INTELLECTUAL PROPERTY RIGHTS.

These resources are intended for skilled developers designing with TI products. You are solely responsible for (1) selecting the appropriate

TI products for your application, (2) designing, validating and testing your application, and (3) ensuring your application meets applicable

standards, and any other safety, security, or other requirements. These resources are subject to change without notice. TI grants you

permission to use these resources only for development of an application that uses the TI products described in the resource. Other

reproduction and display of these resources is prohibited. No license is granted to any other TI intellectual property right or to any third party

intellectual property right. TI disclaims responsibility for, and you will fully indemnify TI and its representatives against, any claims, damages,

costs, losses, and liabilities arising out of your use of these resources.

TI’s products are provided subject to TI’s Terms of Sale (https:www.ti.com/legal/termsofsale.html) or other applicable terms available either

on ti.com or provided in conjunction with such TI products. TI’s provision of these resources does not expand or otherwise alter TI’s

applicable warranties or warranty disclaimers for TI products.IMPORTANT NOTICE

Mailing Address: Texas Instruments, Post Office Box 655303, Dallas, Texas 75265


型号：	LM73606QURNPRQ1
厂家：	TEXAS INSTRUMENTS
描述：	LM7360x-Q1 3.5-V to 36-V, 5-A or 6-A Synchronous Step-Down Voltage Converter
文件：	总65页 (文件大小：5702K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

LM73606QURNPRQ1 [TI]

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