LTC3611IWP-TRPBF_技术文档

LTC3611

10A, 32V Monolithic

Synchronous Step-Down

DC/DC Converter

DESCRIPTION

FEATURES

TheLTC^®3611isahighefﬁciency,monolithicsynchronous

step-down DC/DC converter that can deliver up to 10A

output current from a 4.5V to 32V (36V maximum) input

supply. It uses a constant on-time valley current mode

control architecture to deliver very low duty cycle opera-

tion at high frequency with excellent transient response.

Theoperatingfrequencyisselectedbyanexternalresistor

n

10A Output Current

n

Wide V Range = 4.5V to 32V (36V Maximum)

IN

n

Internal N-Channel MOSFETs

True Current Mode Control

Optimized for High Step-Down Ratios

n

t

≤ 100ns

0N(MIN)

n

Extremely Fast Transient Response

Stable with Ceramic C

and is compensated for variations in V and V

.

OUT

IN

OUT

1ꢀ 0.6V Voltage Reference

The LTC3611 can be conﬁgured for discontinuous or

forced continuous operation at light load. Forced continu-

ous operation reduces noise and RF interference while

discontinuous mode provides high efﬁciency by reducing

switching losses at light loads.

Power Good Output Voltage Monitor

Adjustable On-Time/Switching Frequency (>1MHz)

Adjustable Current Limit

Programmable Soft-Start

Output Overvoltage Protection

Optional Short-Circuit Shutdown Timer

Low Shutdown I : 15μA

Available in a 9mm × 9mm 64-Pin QFN Package

Fault protection is provided by internal foldback current

limiting,anoutputovervoltagecomparatorandanoptional

short-circuitshutdowntimer.Soft-startcapabilityforsup-

ply sequencing is accomplished using an external timing

capacitor.Theregulatorcurrentlimitisuserprogrammable.

A power good output voltage monitor indicates when

the output is in regulation. The LTC3611 is available in a

compact 9mm × 9mm QFN package.

Q

APPLICATIONS

n

Point of Load Regulation

Distributed Power Systems

n

L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other

trademarks are the property of their respective owners. Protected by U.S. Patents including

5481178, 6100678, 6580258, 5847554, 6304066.

TYPICAL APPLICATION

Efﬁciency and Power Loss vs

Load Current

High Efﬁciency Step-Down Converter

100

90

80

70

60

50

40

30

20

10

0

10000

1000

100

10

V

= 2.5V

182k

OUT

V

OUT

V

I

0.1ꢀF

ON

V

IN

= 5V

V

IN

4.5V TO 32V

RUN/SS

V

IN

V

= 25V

IN

10ꢀF

×3

100pF

LTC3611

1ꢀH

V

2.5V

10A

OUT

SW

POWER LOSS,

= 5V

680pF

0.22ꢀF

100ꢀF

×2

V

IN

I

BOOST

TH

12.5k

POWER LOSS,

SGND INTV

CC

30.1k

9.5k

V

IN

= 25V

FCB

39.2k

11k

1

4.7ꢀF

V

INTV

CC

RNG

0.01

0.1

1

10

PGND

LOAD CURRENT (A)

PGOOD

3611 TA01b

EXTV

CC

V

FB

3611 TA01a

3611fb

1

LTC3611

ABSOLUTE MAXIMUM RATINGS

PIN CONFIGURATION

(Note 1)

TOP VIEW

Input Supply Voltage (V , I ).................. 36V to –0.3V

IN ON

Boosted Topside Driver Supply Voltage

(BOOST) ................................................ 42V to –0.3V

SW Voltage............................................... 36V to –5V

INTV , EXTV , (BOOST – SW), RUN/SS,

PGND 1

65

48 SGND

47 SGND

46 SGND

45 SGND

PGND 2

PGND

CC

PGND 3

SW 4

PGOOD Voltages...................................... 7V to –0.3V

FCB, V , V

TH FB

Operating Temperature Range

Voltages............ INTV + 0.3V to –0.3V

ON RNG

CC

SW 5

44 EXTV

CC

SW 6

43 V

FB

I , V Voltages....................................... 2.7V to –0.3V

SW 7

42 SGND

41 I

66

SW

SW 8

SW 9

ON

(Note 4) ............................................. –40°C to 125°C

Junction Temperature (Note 2) ............................. 125°C

Storage Temperature Range...................–55°C to 125°C

40 SGND

39 FCB

SW 10

SW 11

68

SGND

38 I

TH

PV 12

IN

37 V

RNG

PV 13

IN

36 PGOOD

35 V

67

PV

PV 14

IN

ON

IN

PV 15

IN

34 SGND

33 SGND

PV 16

IN

WP PACKAGE

64-LEAD (9mm × 9mm) QFN MULTIPAD

T

= 125°C, θ = 28°C/W

JA

JMAX

ORDER INFORMATION

LEAD FREE FINISH

LTC3611EWP#PBF

LTC3611IWP#PBF

LEAD BASED FINISH

LTC3611EWP

TAPE AND REEL

PART MARKING*

LTC3611WP

PACKAGE DESCRIPTION

TEMPERATURE RANGE

–40°C to 125°C

LTC3611EWP#TRPBF

LTC3611IWP#TRPBF

TAPE AND REEL

64-Lead (9mm × 9mm) Plastic QFN

PACKAGE DESCRIPTION

LTC3611WP

–40°C to 125°C

PART MARKING*

LTC3611WP

TEMPERATURE RANGE

–40°C to 125°C

LTC3611EWP#TR

LTC3611IWP#TR

64-Lead (9mm × 9mm) Plastic QFN

LTC3611IWP

LTC3611WP

–40°C to 125°C

Consult LTC Marketing for parts speciﬁed with wider operating temperature ranges. *The temperature grade is identiﬁed by a label on the shipping container.

For more information on lead free part marking, go to: http://www.linear.com/leadfree/

For more information on tape and reel speciﬁcations, go to: http://www.linear.com/tapeandreel/

3611fb

2

LTC3611

ELECTRICAL CHARACTERISTICS ^Thel denotes the speciﬁcations which apply over the full operating

temperature range, otherwise speciﬁcations are at T_A= 25°C. V_IN= 15V unless otherwise noted.

SYMBOL

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

Main Control Loop

V

Operating Input Voltage Range

4.5

32

V

IN

I

Input DC Supply Current

Normal

Shutdown Supply Current

Q

900

15

2000

30

ꢀA

V

Feedback Reference Voltage

LTC3611E

LTC3611I

I

= 1.2V (Note 3)

TH

FB

–40°C ≤ T ≤ 85°C

0.594

0.590

0.600

0.606

0.610

V

J

l

–40°C ≤ T ≤ 125°C

J

ΔV

Feedback Voltage Line Regulation

Feedback Voltage Load Regulation

Feedback Input Current

V

= 4V to 30V, I = 1.2V (Note 3)

0.002

–0.05

–5

%/V

%

FB(LINEREG)

FB(LOADREG)

IN

TH

I

= 0.5V to 1.9V (Note 3)

= 0.6V

–0.3

50

TH

I

V

nA

mS

V

FB

l

g

Error Ampliﬁer Transconductance

Forced Continuous Threshold

Forced Continuous Pin Current

On-Time

I

= 1.2V (Note 3)

1.4

1.7

2

m(EA)

TH

V

0.54

0.6

0.66

–2

FCB

I

t

V

= 0.6V

FCB

–1

ꢀA

FCB

ON

I

= 60μA, V = 1.5V

190

250

120

310

ns

ON

= 60μA, V = 0V

ON

t

I

Minimum On-Time

I

= 180μA, V = 0V

60

100

500

ns

ON(MIN)

ON

Minimum Off-Time

Maximum Valley Current

= 30μA, V = 1.5V

290

OFF(MIN)

ON

l

V

= 0V, V = 0.56V, FCB = 0V

6

8

10

15

A

VALLEY(MAX)

RNG

FB

= 1V, V = 0.56V, FCB = 0V

FB

I

Maximum Reverse Valley Current

V

= 0V, V = 0.64V, FCB = 0V

–4

–6

–8

–10

A

VALLEY(MIN)

RNG

FB

= 1V, V = 0.64V, FCB = 0V

FB

ΔV

Output Overvoltage Fault Threshold

RUN Pin Start Threshold

7

10

1.5

4

13

2

%

V

FB(OV)

l

V

0.8

RUN/SS(ON)

RUN/SS(LE)

RUN/SS(LT)

RUN/SS(C)

RUN/SS(D)

RUN Pin Latchoff Enable Threshold

RUN Pin Latchoff Threshold

Soft-Start Charge Current

RUN/SS Pin Rising

RUN/SS Pin Falling

4.5

4.2

–3

3

V

3.5

–1.2

1.8

3.4

3.5

V

I

V

= 0V

–0.5

0.8

ꢀA

V

RUN/SS

Soft-Start Discharge Current

Undervoltage Lockout

= 4.5V, V = 0V

FB

l

V

Falling

3.9

4

IN(UVLO)

IN

Undervoltage Lockout Release

Rising

V

IN(UVLOR)

R

Top Switch On-Resistance

Bottom Switch On-Resistance

15

9

22

14

mΩ

DS(ON)

3611fb

3

LTC3611

ELECTRICAL CHARACTERISTICS ^Thel denotes the speciﬁcations which apply over the full operating

temperature range, otherwise speciﬁcations are at T_A= 25°C. V_IN= 15V unless otherwise noted.

SYMBOL

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

Internal V Regulator

CC

l

V

Internal V Voltage

6V < V < 30V, V = 4V

EXTVCC

4.7

5

5.6

2

V

%

INTVCC

CC

IN

ΔV

Internal V Load Regulation

I

= 0mA to 20mA, V

= 4V

–0.1

4.7

LDO(LOADREG)

EXTVCC

CC

EXTVCC

V

EXTV Switchover Voltage

= 20mA, V

Rising

4.5

V

CC

EXTVCC

ΔV

EXTV Switch Drop Voltage

= 5V

150

500

300

m/V

EXTVCC

CC

EXTV Switchover Hysteresis

EXTVCC(HYS)

CC

PGOOD Output

ΔV

PGOOD Upper Threshold

PGOOD Lower Threshold

PGOOD Hysteresis

V

Rising

7

10

–10

1

13

–13

2.5

0.4

%

V

FBH

FB

Falling

–7

FBL

FB

Returning

FB(HYS)

FB

V

PGOOD Low Voltage

I

= 5mA

0.15

PGL

PGOOD

Note 3: The LTC3611 is tested in a feedback loop that adjusts V to

Note 1: Stresses beyond those listed under Absolute Maximum Ratings

may cause permanent damage to the device. Exposure to any Absolute

Maximum Rating condition for extended periods may affect device

reliability and lifetime.

FB

achieve a speciﬁed error ampliﬁer output voltage (I ). The speciﬁcation at

TH

85°C is not tested in production. This speciﬁcation is assured by design,

characterization, and correlation to testing at 125°C.

Note 4: The LTC3611E is guaranteed to meet performance speciﬁcations

from 0°C to 125°C. Speciﬁcations over the –40°C to 125°C operating

temperature range are assured by design, characterization and correlation

with statistical process controls. The LTC3611I is guaranteed over the full

–40°C to 125°C operating temperature range.

Note 2: T is calculated from the ambient temperature T and power

J

A

dissipation P as follows:

D

T = T + (P • 28°C/W) (θ is simulated per JESD51-7 high

J

A

D

JA

effective thermal conductivity test board)

θ

= 1°C/W (θ is simulated when heatsink is applied at the

JC

bottom of the package)

TYPICAL PERFORMANCE CHARACTERISTICS

Transient Response

(Discontinuous Mode)

Transient Response

Start-Up

V

OUT

200mV/DIV

OUT

200mV/DIV

RUN/SS

2V/DIV

IL

5A/DIV

IL

5A/DIV

V

OUT

1V/DIV

I

L

5A/DIV

LOAD

5A/DIV

3611 G03

3611 G01

3611 G02

40ms/DIV

40ꢀs/DIV

V

= 25V

LOAD STEP 0A TO 8A

LOAD = 1A TO 10A

IN

OUT

= 2.5V

= 0.5Ω

V

= 25V

V

= 25V

IN

OUT

R

= 2.5V

LOAD

OUT

FCB = 0

FIGURE 6 CIRCUIT

FCB = INTV

CC

FIGURE 6 CIRCUIT

3611fb

4

LTC3611

TYPICAL PERFORMANCE CHARACTERISTICS

Efﬁciency vs Load Current

Efﬁciency vs Input Voltage

Frequency vs Input Voltage

100

90

80

70

60

50

100

95

90

85

80

640

600

560

520

480

440

400

FCB = 5V

FIGURE 6 CIRCUIT

DISCONTINUOUS

I

= 10A

LOAD

CONTINUOUS

I

= 10A

LOAD

I

= 0A

30

LOAD

V

= 12V

IN

OUT

= 2.5V

I

= 1A

LOAD

20

EXTV = 5V

CC

FCB = 0V

FIGURE 6 CIRCUIT

0.01

0.1

1 10

5

10

15

25

30

35

5

10 15

20

25

35

LOAD CURRENT (A)

INPUT VOLTAGE (V)

3611 G06

3611 G04

3611 G05

Frequency vs Load Current

CONTINUOUS MODE

Load Regulation

I_THVoltage vs Load Current

0.80

0.60

0.40

0.20

0

650

600

550

500

450

400

350

300

250

200

150

100

50

2.5

2.0

1.5

1.0

0.5

0

FIGURE 6 CIRCUIT

DISCONTINUOUS MODE

CONTINUOUS

MODE

–0.20

–0.40

–0.60

–0.80

DISCONTINUOUS

MODE

0

15

0

2

4

6

8

10

0

2

4

6

8

10

0

5 10

LOAD CURRENT (A)

3611 G07

3611 G08

3611 G09

Load Current vs I_THVoltage and

V_RNG

On-Time vs I_ONCurrent

On-Time vs V_ONVoltage

10000

1000

100

1000

800

600

400

200

0

25

20

15

10

5

V

VON

= 0V

I

= 30ꢀA

ON

V

RNG

= 1V

0.7V

0.5V

0

–5

–10

10

0

1

2

3

0

0.5

1

I

1.5

2

2.5

3

1

10

100

I

ON

CURRENT (ꢀA)

V

ON

VOLTAGE (V)

TH

3611 G11

3611 G12

3611 G10

3611fb

5

LTC3611

TYPICAL PERFORMANCE CHARACTERISTICS

Maximum Valley Current Limit vs

RUN/SS Voltage

On-Time vs Temperature

V_RNGVoltage

20

18

15

12

9

300

250

200

150

FIGURE 6 CIRCUIT

I

= 30ꢀA

VON

ION

V

= 0V

15

10

5

6

100

50

0

3

0

0.5

0.6

0.7

0.8

0.9

1

1.65 1.9 2.15 2.4 2.65 2.9 3.15 3.4

–50 –25

0

25

50

75

100 125

V

RNG

VOLTAGE (V)

RUN/SS VOLTAGE (V)

TEMPERATURE (°C)

3611 G15

3611 G16

3611 G13

Maximum Valley Current Limit vs

Temperature

Input Voltage vs Maximum

Valley Current

Maximum Valley Current Limit

in Foldback

20

15

10

20

18

V

RNG

= 1V

V

RNG

= 1V

16

14

12

15

10

5

10

8

5

0

6

0

4

–50 –25

0

25

50

75 100 125

8

12 16 20 24 28 32 36

INPUT VOLTAGE (V)

3611 G27

0

0.1

0.2

0.3

(V)

0.4

0.5

0.6

4

TEMPERATURE (°C)

V

FB

3611 G17

3611 G14

Feedback Reference Voltage

vs Temperature

Error Ampliﬁer g_mvs Temperature

2.0

1.8

1.6

1.4

1.2

1.0

0.62

0.61

0.60

0.59

0.58

–50 –25

0

25

50

75 100 125

–50 –25

0

25

50

75

125

100

TEMPERATURE (°C)

3611 G18

3611 G19

3611fb

6

LTC3611

TYPICAL PERFORMANCE CHARACTERISTICS

Input and Shutdown Currents

vs Input Voltage

INTV_CCLoad Regulation

I_EXTVCCvs Frequency

1400

1200

1000

800

600

400

200

0

40

35

30

25

20

15

10

5

30

25

20

15

10

5

0.30

0.20

0.10

0

V

= 24V

IN

OUT

= 2.5V

EXTV OPEN

CC

SHUTDOWN

–0.10

–0.20

–0.30

–0.40

EXTV = 5V

CC

0

5

10

15

20

25

30

400

500

600

700

800

900 1000

0

10

20

30

40

50

INPUT VOLTAGE (V)

FREQUENCY (KHz)

INTV LOAD CURRENT (mA)

CC

3611 G20

3611 G21

3611 G28

EXTV_CCSwitch Resistance

vs Temperature

RUN/SS Pin Current

vs Temperature

FCB Pin Current vs Temperature

10

8

3

2

0

–0.25

–0.50

–0.75

PULL-DOWN CURRENT

6

1

4

0

–1.00

–1.25

–1.50

2

–1

PULL-UP CURRENT

0 25 50 75 100 125

0

–2

–50 –25

0

25

50

75

100 125

–50 –25

0

25

50

75 100 125

–50 –25

TEMPERATURE (°C)

3611 G24

3611 G23

3611 G22

RUN/SS Pin Current

vs Temperature

Undervoltage Lockout Threshold

vs Temperature

5.0

4.5

4.0

3.5

4.0

3.5

3.0

2.5

LATCHOFF ENABLE

LATCHOFF THRESHOLD

3.0

2.0

–50 –25

0

25

50

75 100 125

–50 –25

0

25

50

75 100 125

TEMPERATURE (°C)

3611 G25

3611 G26

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LTC3611

PIN FUNCTIONS

PGND (Pins 1, 2, 3, 56, 57, 58, 59, 60, 61, 62, 63, 64,

V

(Pin 37): Current Limit Range Input. The voltage

RNG

65): Power Ground. Connect this pin closely to the (–)

at this pin adjusts maximum valley current and can be

set from 0.7V to 1V by a resistive divider from INTV .

terminal of C

and the (–) terminal of C .

VCC

IN

CC

It defaults to 0.7V if the V

results in a typical 10A current limit.

I (Pin38):CurrentControlThresholdandErrorAmpliﬁer

TH

Compensation Point. The current comparator threshold

increases with this control voltage. The voltage ranges

from 0V to 2.4V with 0.8V corresponding to zero sense

voltage (zero current).

pin is tied to ground which

RNG

SW (Pins 4, 5, 6, 7, 8, 9, 10, 11, 26, 55, 66): Switch

Node Connection to the Inductor. The (–) terminal of the

bootstrapcapacitorC alsoconnectshere.Thispinswings

B

from a diode voltage drop below ground up to V .

IN

PV (Pins 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22,

IN

23, 24, 25, 67): Main Input Supply. Decouple this pin to

power PGND with the input capacitance C .

IN

FCB (Pin 39): Forced Continuous Input. Tie this pin to

NC (Pin 27): No Connection.

ground to force continuous synchronous operation at low

SGND (Pins 28, 31, 32, 33, 34, 40, 42, 45, 46, 47, 48,

49, 50, 68): Signal Ground. All small-signal components

and compensation components should connect to this

ground, which in turn connects to PGND at one point.

load,toINTV to enable discontinuous mode operation at

CC

low load or to a resistive divider from a secondary output

when using a secondary winding.

I

(Pin41):On-TimeCurrentInput.TiearesistorfromV

IN

ON

BOOST (Pin 29): Boosted Floating Driver Supply. The

to this pin to set the one-shot timer current and thereby

(+) terminal of the bootstrap capacitor C connects here.

set the switching frequency.

B

This pin swings from a diode voltage drop below INTV

CC

V

(Pin 43): Error Ampliﬁer Feedback Input. This pin

FB

up to V + INTV .

IN

CC

connects the error ampliﬁer input to an external resistive

RUN/SS (Pin 30): Run Control and Soft-Start Input. A

capacitor to ground at this pin sets the ramp time to full

output current (approximately 3s/μF) and the time delay

for overcurrent latchoff (see Applications Information).

Forcing this pin below 0.8V shuts down the device.

divider from V

.

OUT

EXTV (Pin 44): External V Input. When EXTV ex-

CC

ceeds 4.7V, an internal switch connects this pin to INTV

CC

andshutsdowntheinternalregulatorsothatcontrollerand

gate drive power is drawn from EXTV . Do not exceed

CC

V

(Pin 35): On-Time Voltage Input. Voltage trip point

7V at this pin and ensure that EXTV < V .

ON

CC

IN

for the on-time comparator. Tying this pin to the output

SV (Pins 51, 52): Supply pin for internal PWM controller.

IN

volt-age or an external resistive divider from the output

makes the on-time proportional to V . The compara-

INTV (Pins 53, 54): Internal 5V Regulator Output. The

OUT

CC

tor input defaults to 0.7V when the pin is grounded and

driver and control circuits are powered from this voltage.

Decouple this pin to power ground with a minimum of

4.7μF low ESR tantalum or ceramic capacitor.

defaults to 2.4V when the pin is tied to INTV . Tie this

CC

pin to INTV in high V

R

applications to use a lower

CC

OUT

value.

ON

PGOOD (Pin 36): Power Good Output. Open drain logic

output that is pulled to ground when the output voltage

is not within 10% of the regulation point.

3611fb

8

LTC3611

FUNCTIONAL DIAGRAM

R

ON

SV

V

ON

35

I

FCB

39

EXTV

44

IN

ON

CC

41

51, 52

4.7V

PV

IN

0.7V

2.4V

1ꢀA

+

–

12, 13, 14, 15,

16, 17, 18, 19,

20, 21, 22, 23,

24, 25, 67

0.6V

REF

C

IN

0.6V

5V

REG

INTV

CC

+

–

53, 54

F

BOOST

29

V

I

VON

ION

t

=

(10pF)

R

S

ON

C

B

Q

FCNT

M1

ON

L1

20k

D

B

SW

+

–

+

–

V

OUT

4, 5, 6, 7, 8, 9,

10, 11, 26, 55,

66

SWITCH

LOGIC

I

REV

CMP

SHDN

OV

+

1.4V

0.7V

1

C

OUT

M2

C

VCC

V

RNG

37

PGND

×

1, 2, 3, 56, 57,

58, 59, 60, 61,

62, 63, 64, 65

(0.5 TO 2)

36

PGOOD

R2

0.54V

240k

+

1V

Q2 Q4

UV

–

Q6

I

THB

43

V

FB

Q3 Q1

R1

+

–

OV

SGND

+

–

0.66V

0.8V

28, 31, 32, 33, 34,

40, 42, 45, 46, 47,

48, 49, 50, 68

RUN

SHDN

SS

–

+

1.2ꢀA

EA

×3.3

NC

–

+

27

6V

0.6V

0.4V

38

30

3611 FD

I

RUN/SS

TH

C

SS

3611fb

9

LTC3611

OPERATION

Main Control Loop

Overvoltage and undervoltage comparators OV and UV

pull the PGOOD output low if the output feedback volt-

age exits a 10% window around the regulation point.

Furthermore, in an overvoltage condition, M1 is turned

off and M2 is turned on and held on until the overvoltage

condition clears.

The LTC3611 is a high efﬁciency monolithic synchronous,

step-down DC/DC converter utilizing a constant on-time,

currentmodearchitecture.Itoperatesfromaninputvoltage

rangeof4.5Vto32Vandprovidesaregulatedoutputvoltage

at up to 10A of output current. The internal synchronous

powerswitchincreasesefﬁciencyandeliminatestheneed

for an external Schottky diode. In normal operation, the

top MOSFET is turned on for a ﬁxed interval determined

by a one-shot timer OST. When the top MOSFET is turned

off, the bottom MOSFET is turned on until the current

Foldback current limiting is provided if the output is

shorted to ground. As V drops, the buffered current

FB

threshold voltage I

is pulled down by clamp Q3 to

THB

a 1V level set by Q4 and Q6. This reduces the inductor

valley current level to one sixth of its maximum value as

comparator I

trips, restarting the one-shot timer and

V

approaches 0V.

CMP

FB

initiating the next cycle. Inductor current is determined

by sensing the voltage between the PGND and SW pins

using the bottom MOSFET on-resistance. The voltage on

Pulling the RUN/SS pin low forces the controller into its

shutdown state, turning off both M1 and M2. Releasing

the pin allows an internal 1.2μA current source to charge

the I pin sets the comparator threshold corresponding

TH

up an external soft-start capacitor C . When this voltage

SS

to inductor valley current. The error ampliﬁer EA adjusts

reaches1.5V,thecontrollerturnsonandbeginsswitching,

this voltage by comparing the feedback signal V from

FB

but with the I voltage clamped at approximately 0.6V

TH

the output voltage with an internal 0.6V reference. If the

below the RUN/SS voltage. As C continues to charge,

SS

load current increases, it causes a drop in the feedback

the soft-start current limit is removed.

voltage relative to the reference. The I voltage then

TH

rises until the average inductor current again matches

INTV /EXTV Power

CC

the load current.

PowerforthetopandbottomMOSFETdriversandmostof

the internal controller circuitry is derived from the INTV

At light load, the inductor current can drop to zero and

become negative. This is detected by current reversal

CC

pin. The top MOSFET driver is powered from a ﬂoating

bootstrap capacitor C . This capacitor is recharged from

INTV throughanexternalSchottkydiodeD whenthetop

MOSFET is turned off. When the EXTV pin is grounded,

comparator I

which then shuts off M2 (see Func-

REV

B

tionalDiagram),resultingindiscontinuousoperation.Both

CC

B

switcheswillremainoffwiththeoutputcapacitorsupplying

the load current until the I voltage rises above the zero

CC

TH

an internal 5V low dropout regulator supplies the INTV

CC

current level (0.8V) to initiate another cycle. Discontinu-

ous mode operation is disabled by comparator F when

the FCB pin is brought below 0.6V, forcing continuous

synchronous operation.

power from V . If EXTV rises above 4.7V, the internal

IN

CC

regulator is turned off, and an internal switch connects

EXTV to INTV . This allows a high efﬁciency source

CC

connected to EXTV , such as an external 5V supply or

CC

a secondary output from the converter, to provide the

INTV power. Voltages up to 7V can be applied to EX T V

The operating frequency is determined implicitly by the

top MOSFET on-time and the duty cycle required to main-

tain regulation. The one-shot timer generates an on-time

that is proportional to the ideal duty cycle, thus holding

CC

for additional gate drive. If the input voltage is low and

INTV drops below 3.5V, undervoltage lockout circuitry

CC

prevents the power switches from turning on.

frequency approximately constant with changes in V .

IN

The nominal frequency can be adjusted with an external

resistor R .

ON

3611fb

10

LTC3611

APPLICATIONS INFORMATION

ThebasicLTC3611applicationcircuitisshownonthefront

page of this data sheet. External component selection is

primarily determined by the maximum load current. The

LTC3611usestheon-resistanceofthesynchronouspower

MOSFETfordeterminingtheinductorcurrent.Thedesired

amount of ripple current and operating frequency also

Operating Frequency

The choice of operating frequency is a tradeoff between

efﬁciency and component size. Low frequency operation

improves ef ﬁciency by reducing MOSFET switching losses

butrequireslargerinductanceand/orcapacitanceinorder

to maintain low output ripple voltage.

determinestheinductorvalue.Finally,C isselectedforits

IN

The operating frequency of LTC3611 applications is de-

termined implicitly by the one-shot timer that controls the

ability to handle the large RMS current into the converter

and C

is chosen with low enough ESR to meet the

OUT

on-time t of the top MOSFET switch. The on-time is set

output voltage ripple and transient speciﬁcation.

ON

by the current into the I pin and the voltage at the V

ON

V

ON

and PGOOD

pin according to:

The LTC3611 has an open-drain PGOOD output that

indicates when the output voltage is within 10% of the

V

t_ON

=

^VON(10pF)

I_ION

regulation point. The LTC3611 also has a V pin that

ON

allows the on-time to be adjusted. Tying the V pin high

ON

Tying a resistor R from V to the I pin yields an

ON

IN

ON

resultsinlowervaluesforR which is useful in high V

ON

OUT

on-time inversely proportional to V . The current out of

IN

applications. The V pin also provides a means to adjust

ON

the I pin is:

ON

the on-time to maintain constant frequency operation in

V

applications where V

changes and to correct minor

IN

OUT

I

=

ION

frequency shifts with changes in load current.

R_ON

V

Pin and I Adjust

For a step-down converter, this results in approximately

constant frequency operation as the input supply varies:

RNG

LIMIT

The V

pin is used to adjust the maximum inductor

RNG

valley current, which in turn determines the maximum

average output current that the LTC3611 can deliver. The

maximum output current is given by:

V_OUT

V_VONR_ON(10pF)

f =

[Hz]

I

= I

+ 1/2 ΔI ,

Toholdfrequencyconstantduringoutputvoltagechanges,

OUT(MAX)

VALLEY(MAX)

L

tie the V pin to V or to a resistive divider from V

ON

OUT

The I

CurrentLimitvsV

Characteristics.

is shown in the ﬁgure “Maximum Valley

VALLEY(MAX)

when V

> 2.4V. The V pin has internal clamps that

ON

Voltage”intheTypicalPerformance

RNG

limit its input to the one-shot timer. If the pin is tied below

0.7V,theinputtotheone-shotisclampedat0.7V.Similarly,

if the pin is tied above 2.4V, the input is clamped at 2.4V.

An external resistor divider from INTV can be used to

set the voltage on the V

be simply tied to ground force a default value equivalent

to 0.7V. Do not ﬂoat the V pin.

CC

pin from 1V to 1.4V, or it can

In high V

applications, tying V to INTV so that

RNG

OUT

ON CC

the comparator input is 2.4V results in a lower value for

R . Figures 1a and 1b show how R relates to switching

RNG

ON

frequency for several common output voltages.

3611fb

11

LTC3611

APPLICATIONS INFORMATION

1000

ascurrentincreases, constantfrequencyoperationcanbe

maintained. This is accomplished with a resistive divider

from the I pin to the V pin and V . The values

TH

ON

OUT

required will depend on the parasitic resistances in the

V

OUT

= 3.3V

speciﬁc application. A good starting point is to feed about

V

OUT

= 1.5V

V

OUT

= 2.5V

25% of the voltage change at the I pin to the V pin

TH

ON

as shown in Figure 2a. Place capacitance on the V pin

ON

to ﬁlter out the I variations at the switching frequency.

TH

The resistor load on I reduces the DC gain of the error

TH

amp and degrades load regulation, which can be avoided

100

1000

(kΩ)

10000

by using the PNP emitter follower of Figure 2b.

R

ON

3611 F01a

Minimum Off-time and Dropout Operation

Figure 1a. Switching Frequency vs R_ON(V_ON= 0V)

The minimum off-time t

is the smallest amount of

OFF(MIN)

1000

time that the LTC3611 is capable of turning on the bottom

MOSFET, tripping the current comparator and turning the

MOSFET back off. This time is generally about 250ns.

The minimum off-time limit imposes a maximum duty

V

= 12V

OUT

V

= 5V

OUT

cycle of t /(t

t

). If the maximum duty cycle

ON ON + OFF(MIN)

V

OUT

= 3.3V

is reached, due to a dropping input voltage for example,

then the output will drop out of regulation. The minimum

input voltage to avoid dropout is:

t

_ON+ t_OFF(MIN)

100

V_IN(MIN)= V_OUT

100

1000

(kΩ)

10000

t_ON

R

ON

3611 F01b

Figure 1b. Switching Frequency vs R_ON(V_ON= INTV_CC

)

A plot of maximum duty cycle vs frequency is shown in

Figure 3.

Because the voltage at the I pin is about 0.7V, the cur-

ON

rent into this pin is not exactly inversely proportional to

Setting the Output Voltage

V , especially in applications with lower input voltages.

IN

The LTC3611 develops a 0.6V reference voltage between

To correct for this error, an additional resistor R

con-

ON2

the feedback pin, V , and the signal ground as shown in

FB

nectedfromtheI pintothe5VINTV supply will fur ther

ON

CC

Figure 6. The output voltage is set by a resistive divider

stabilize the frequency.

according to the following formula:

5V

0.7V

R_ON2

=

R_ON

R2

R1

ꢀ

ꢁ

ꢃ

ꢄ

V_OUT= 0.6V 1+

ꢂ

ꢅ

Changes in the load current magnitude will also cause

frequency shift. Parasitic resistance in the MOSFET

switches and inductor reduce the effective voltage across

the inductance, resulting in increased duty cycle as the

loadcurrentincreases.Bylengtheningtheon-timeslightly

Toimprovethefrequencyresponse,afeedforwardcapaci-

tor C1 may also be used. Great care should be taken to

route the V line away from noise sources, such as the

FB

inductor or the SW line.

3611fb

12

LTC3611

APPLICATIONS INFORMATION

R

VON1

ripple. Highest efﬁciency operation is obtained at low

frequency with small ripple current. However, achieving

this requires a large inductor. There is a tradeoff between

component size, efﬁciency and operating frequency.

30k

V

OUT

ON

C

VON

R

VON2

100k

0.01ꢀF

LTC3611

R

C

I

TH

A reasonable starting point is to choose a ripple current

C

that is about 40% of I

. The largest ripple current

OUT(MAX)

occurs at the highest V . To guarantee that ripple current

IN

(2a)

does not exceed a speciﬁed maximum, the inductance

R

VON1

3k

should be chosen according to:

V

ON

OUT

C

R

VON

VON2

10k

ꢁ

ꢄ ꢁ

ꢄ

V_OUT

f ꢀI

V_OUT

0.01ꢀF

10k

LTC3611

L =

1ꢇ

INTV

ꢃ

ꢆ ꢃ

ꢆ

CC

R

C

V

ꢂ

ꢅ ꢂ

ꢅ

L(MAX)

IN(MAX)

Q1

2N5087

I

TH

C

3611 F02

Once the value for L is known, the type of inductor must

be selected. High efﬁciency converters generally cannot

affordthecorelossfoundinlowcostpowderedironcores.

A variety of inductors designed for high current, low volt-

ageapplicationsareavailablefrommanufacturerssuchas

Sumida, Panasonic, Coiltronics, Coilcraft and Toko.

(2b)

Figure 2. Correcting Frequency Shift with Load Current Changes

2.0

C and C

Selection

OUT

IN

1.5

DROPOUT

REGION

The input capacitance C is required to ﬁlter the square

IN

wavecurrentatthedrainofthetopMOSFET.UsealowESR

1.0

0.5

0

capacitor sized to handle the maximum RMS current.

V_OUT

V

V_OUT

IN

I_RMSꢀI_OUT(MAX)

–1

V

IN

0

0.25

0.50

0.75

1.0

This formula has a maximum at V = 2V , where

IN

OUT

DUTY CYCLE (V /V

)

OUT IN

3611 F03

I

= I

/2. This simple worst-case condition is

RMS

OUT(MAX)

Figure 3. Maximum Switching Frequency vs Duty Cycle

commonly used for design because even signiﬁcant de-

viations do not offer much relief. Note that ripple current

ratings from capacitor manufacturers are often based on

only 2000 hours of life which makes it advisable to derate

the capacitor.

Inductor Selection

Given the desired input and output voltages, the induc-

tor value and operating frequency determine the ripple

current:

The selection of C

is primarily determined by the ESR

OUT

requiredtominimizevoltagerippleandloadsteptransients.

The output ripple ΔV

is approximately bounded by:

OUT

ꢁ

ꢃ

ꢂ

ꢄ

ꢆ

ꢅ

ꢁ

_OUTꢄ

V

V_OUT

f L

ꢀI =

1ꢇ

L

ꢃ

ꢆ

ꢂ

ꢅ

ꢇ

1

V

ꢂ

ꢅ

IN

ꢀV_OUTꢁ ꢀI_LESR+

ꢄ

8fC

ꢃ

_OUTꢆ

Lower ripple current reduces core losses in the inductor,

ESR losses in the output capacitors and output voltage

3611fb

13

LTC3611

APPLICATIONS INFORMATION

Since ΔI increases with input voltage, the output ripple

Discontinuous Mode Operation and FCB Pin

L

is highest at maximum input voltage. Typically, once the

ESR requirement is satisﬁed, the capacitance is adequate

for ﬁltering and has the necessary RMS current rating.

The FCB pin determines whether the bottom MOSFET

remains on when current reverses in the inductor. Tying

this pin above its 0.6V threshold enables discontinuous

operation where the bottom MOSFET turns off when in-

ductor current reverses. The load current at which current

reverses and discontinuous operation begins depends on

the amplitude of the inductor ripple current and will vary

Multiple capacitors placed in parallel may be needed to

meet the ESR and RMS current handling requirements.

Dry tantalum, special polymer, aluminum electrolytic and

ceramiccapacitorsareallavailableinsurfacemountpack-

ages. Special polymer capacitors offer very low ESR but

havelowercapacitancedensitythanothertypes.Tantalum

capacitors have the highest capacitance density but it is

important to only use types that have been surge tested

foruseinswitchingpowersupplies.Aluminumelectrolytic

capacitors have signiﬁcantly higher ESR, but can be used

incost-sensitiveapplicationsprovidingthatconsideration

is given to ripple current ratings and long term reliability.

Ceramic capacitors have excellent low ESR characteris-

tics but can have a high voltage coefﬁcient and audible

piezoelectriceffects.ThehighQofceramiccapacitorswith

traceinductancecanalsoleadtosigniﬁcantringing.When

usedasinputcapacitors,caremustbetakentoensurethat

ringing from inrush currents and switching does not pose

an overvoltage hazard to the power switches and control-

ler. To dampen input voltage transients, add a small 5μF

to 50μF aluminum electrolytic capacitor with an ESR in

the range of 0.5Ω to 2Ω. High performance through-hole

capacitors may also be used, but an additional ceramic

capacitor in parallel is recommended to reduce the effect

of their lead inductance.

with changes in V . Tying the FCB pin below the 0.6V

IN

threshold forces continuous synchronous operation, al-

lowing current to reverse at light loads and maintaining

high frequency operation.

In addition to providing a logic input to force continuous

operation, the FCB pin provides a means to maintain a

ﬂyback winding output when the primary is operating

in discontinuous mode. The secondary output V

is

OUT2

normally set as shown in Figure 4 by the turns ratio N

of the transformer. However, if the controller goes into

discontinuous mode and halts switching due to a light

primary load current, then V

will droop. An external

OUT2

resistor divider from V

to the FCB pin sets a minimum

OUT2

voltage V

below which continuous operation is

has risen above its minimum:

OUT2(MIN)

forced until V

OUT2

R4

R3

ꢀ

ꢁ

ꢃ

ꢄ

V_OUT2(MIN)= 0.6V 1+

ꢂ

ꢅ

Fault Conditions: Current Limit and Foldback

The LTC3611 has a current mode controller which inher-

ently limits the cycle-by-cycle inductor current not only

in steady state operation but also in transient. To further

limit current in the event of a short circuit to ground, the

LTC3611 includes foldback current limiting. If the output

fallsbymorethan25%,thenthemaximumsensevoltageis

progressively lowered to about one sixth of its full value.

Top MOSFET Driver Supply (C , D )

B

AnexternalbootstrapcapacitorC connectedtotheBOOST

B

pinsuppliesthegatedrivevoltageforthetopsideMOSFET.

This capacitor is charged through diode D from INTV

B

CC

when the switch node is low. When the top MOSFET turns

on, the switch node rises to V and the BOOST pin rises

IN

toapproximatelyV +INTV . Theboostcapacitorneeds

IN

CC

INTV Regulator and EXTV Connection

CC

to store about 100 times the gate charge required by the

top MOSFET. In most applications an 0.1μF to 0.47μF, X5R

or X7R dielectric capacitor is adequate.

An internal P-channel low dropout regulator produces the

5V supply that powers the drivers and internal circuitry

withintheLTC3611.TheINTV pincansupplyupto50mA

CC

3611fb

14

LTC3611

APPLICATIONS INFORMATION

SW

PGND

SGND

64 63 62 61 60 59 58 57 56 55 54 53 52 51 50 49

IN4148

1

2

48

47

46

45

44

43

42

41

40

39

38

37

36

35

34

33

PGND

SGND

V

OUT2

PGND

SW

+

C

SEC

1ꢀF

3

4

V

OUT1

T1

1:N

5

+

SW

EXTV

CC

C

OUT

6

SW

V

FB

7

SW

SGND

R4

8

SW

I

ON

LTC3611

9

SW

SGND

FCB

OPTIONAL EXTV

CC

10

11

12

13

14

15

16

SW

CONNECTION

5V < V < 7V

OUT2

SW

I

TH

V

IN

PV

V

RNG

IN

+

R3

PGOOD

C

IN

V

ON

SGND

17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

3611 F04

SGND

SW

Figure 4. Secondary Output Loop and EXTV_CCConnection

3. EXTV connectedtoanoutputderivedboostnetwork.

RMS and must be bypassed to ground with a minimum of

4.7μF tantalum or ceramic capacitor. Good bypassing is

necessary to supply the high transient currents required

by the MOSFET gate drivers.

CC

The low voltage output can be boosted using a charge

pump or ﬂyback winding to greater than 4.7V. The system

will start-up using the internal linear regulator until the

boosted output supply is available.

TheEXTV pin can be used to provide MOSFET gate drive

CC

and control power from the output or another external

Soft-Start and Latchoff with the RUN/SS Pin

source during normal operation. Whenever the EXTV

CC

The RUN/SS pin provides a means to shut down the

LTC3611 as well as a timer for soft-start and overcurrent

latchoff. Pulling the RUN/SS pin below 0.8V puts the

pin is above 4.7V the internal 5V regulator is shut off and

an internal 50mA P-channel switch connects the EXTV

CC

pin to INTV . INTV power is supplied from EXTV

CC

LTC3611 into a low quiescent current shutdown (I <

Q

until this pin drops below 4.5V. Do not apply more than

7V to the EXTV pin and ensure that EXTV ≤ V . The

30μA). Releasing the pin allows an internal 1.2μA current

CC

IN

source to charge up the external timing capacitor C . If

SS

following list summarizes the possible connections for

RUN/SS has been pulled all the way to ground, there is a

EXTV :

CC

delay before starting of about:

1. EXTV grounded. INTV is always powered from the

CC

internal 5V regulator.

1.5V

1.2μA

t_DELAY

=

C = 1.3s/μF C

SS SS

(

)

2. EXTV connectedtoanexternalsupply.Ahighefﬁciency

CC

supply compatible with the MOSFET gate drive require-

When the voltage on RUN/SS reaches 1.5V, the LTC3611

ments (typically 5V) can improve overall efﬁciency.

begins operating with a clamp on I of approximately

TH

3611fb

15

LTC3611

APPLICATIONS INFORMATION

0.9V. As the RUN/SS voltage rises to 3V, the clamp on I

is raised until its full 2.4V range is available. This takes an

additional 1.3s/μF, during which the load current is folded

back until the output reaches 75% of its ﬁnal value.

INTV

CC

R

TH

*

SS

V

IN

RUN/SS

3.3V OR 5V

RUN/SS

*

D2*

R

SS

D1

After the controller has been started and given adequate

2N7002

C

SS

C

SS

time to charge up the output capacitor, C is used as a

SS

3611 F05

short-circuittimer.AftertheRUN/SSpinchargesabove4V,

iftheoutputvoltagefallsbelow75%ofitsregulatedvalue,

then a short-circuit fault is assumed. A 1.8μA current then

*OPTIONAL TO OVERRIDE

OVERCURRENT LATCHOFF

(5a)

(5b)

beginsdischargingC . Ifthefaultconditionpersistsuntil

SS

Figure 5. RUN/SS Pin Interfacing with Latchoff Defeated

the RUN/SS pin drops to 3.5V, then the controller turns

off both power MOSFETs, shutting down the converter

permanently. The RUN/SS pin must be actively pulled

down to ground in order to restart operation.

Efﬁciency Considerations

The percent efﬁciency of a switching regulator is equal to

the output power divided by the input power times 100%.

It is often useful to analyze individual losses to determine

what is limiting the efﬁciency and which change would

produce the most improvement. Although all dissipative

elements in the circuit produce losses, four main sources

account for most of the losses in LTC3611 circuits:

Theovercurrentprotectiontimerrequiresthatthesoft-start

timing capacitor C be made large enough to guarantee

SS

thattheoutputisinregulationbythetimeC hasreached

SS

the 4V threshold. In general, this will depend upon the

size of the output capacitance, output voltage and load

current characteristic. A minimum soft-start capacitor

can be estimated from:

2

1. DC I R losses. These arise from the resistance of the

internalresistanceoftheMOSFETs,inductorandPCboard

traces and cause the efﬁciency to drop at high output

currents. In continuous mode the average output current

ﬂows through L, but is chopped between the top and bot-

–4

C

> C

V

R

(10 [F/V s])

SS

OUT OUT SENSE

Generally 0.1μF is more than sufﬁcient.

Overcurrentlatchoffoperationisnotalwaysneededorde-

sired. Loadcurrentisalreadylimitedduringashort-circuit

by the current foldback circuitry and latchoff operation

can prove annoying during troubleshooting. The feature

can be overridden by adding a pull-up current greater than

5μA to the RUN/SS pin. The additional current prevents

tom MOSFETs. If the two MOSFETs have approximately

2

the same R

, then the DC I R loss for one MOSFET

DS(ON)

can simply be determined by [R

+ R ] • I .

DS(ON)

L O

2. Transition loss. This loss arises from the brief amount

of time the top MOSFET spends in the saturated region

during switch node transitions. It depends upon the

input voltage, load current, driver strength and MOSFET

capacitance, among other factors. The loss is signiﬁcant

at input voltages above 20V and can be estimated from:

the discharge of C during a fault and also shortens

SS

the soft-start period. Using a resistor to V as shown

IN

in Figure 5a is simple, but slightly increases shutdown

current. Connecting a resistor to INTV as shown in

CC

–1

2

Figure 5b eliminates the additional shutdown current,

Transition Loss ≅ (1.7A ) V

I

C

f

IN OUT RSS

but requires a diode to isolate C . Any pull-up network

SS

3. INTV current. This is the sum of the MOSFET driver

CC

must be able to pull RUN/SS above the 4.2V maximum

threshold of the latchoff circuit and overcome the 4μA

maximum discharge current.

and control currents. This loss can be reduced by sup-

plying INTV current through the EXTV pin from a

CC

high efﬁciency source, such as an output derived boost

network or alternate supply if available.

3611fb

16

LTC3611

APPLICATIONS INFORMATION

4. C loss.Theinputcapacitorhasthedifﬁcultjobofﬁltering

Selecting a standard value of 1μH results in a maximum

ripple current of:

IN

the large RMS input current to the regulator. It must have

2

a very low ESR to minimize the AC I R loss and sufﬁcient

2.5V

550kHz 1μH

2.5V

12V

ꢁ

ꢂ

ꢄ

ꢅ

capacitance to prevent the RMS current from causing ad-

ditional upstream losses in fuses or batteries.

ꢀI_L=

1–

= 3.6A

ꢃ

ꢆ

(

)(

)

Other losses, including C

conduction loss during dead time and inductor core loss

generally account for less than 2% additional loss.

ESR loss, Schottky diode D1

OUT

Next, set up V

voltage and check the I

. Tying

RNG

LIMIT

V

to 1V will set the typical current limit to 15A, and

RNG

tying V

to GND will result in a typical current around

RNG

IN

10A. C is chosen for an RMS current rating of about 5A

Whenmakingadjustmentstoimproveefﬁciency,theinput

current is the best indicator of changes in efﬁciency. If

you make a change and the input current decreases, then

the efﬁciency has increased. If there is no change in input

current, then there is no change in efﬁciency.

at 85°C. The output capacitors are chosen for a low ESR

of 0.013Ω to minimize output voltage changes due to

inductor ripple current and load steps. The ripple voltage

will be only:

ΔV

= ΔI

(ESR)

OUT(RIPPLE)

L(MAX)

Checking Transient Response

= (3.6A) (0.013Ω) = 47mV

The regulator loop response can be checked by looking

at the load transient response. Switching regulators take

several cycles to respond to a step in load current. When

However, a 0A to 10A load step will cause an output

change of up to:

a load step occurs, V

immediately shifts by an amount

ΔV

= ΔI

(ESR) = (10A) (0.013Ω) =130mV

OUT

OUT(STEP)

LOAD

equal to ΔI

(ESR), where ESR is the effective series

LOAD

An optional 22μF ceramic output capacitor is included

to minimize the effect of ESL in the output ripple. The

complete circuit is shown in Figure 6.

resistance of C . ΔI

also begins to charge or dis-

OUT

LOAD

chargeC

generating a feedback error signal used by the

OUT

regulator to return V

this recovery time, V

to its steady-state value. During

can be monitored for overshoot

OUT

PC Board Layout Checklist

or ringing that would indicate a stability problem. The I

TH

When laying out a PC board follow one of the two sug-

gested approaches. The simple PC board layout requires

a dedicated ground plane layer. Also, for higher currents,

a multilayer board is recommended to help with heat

sinking of power components.

pin external components shown in Figure 6 will provide

adequate compensation for most applications. For a

detailed explanation of switching control loop theory see

Application Note 76.

Design Example

• The ground plane layer should not have any traces and

it should be as close as possible to the layer with the

LTC3611.

As a design example, take a supply with the following

speciﬁcations: V = 5V to 36V (12V nominal), V

=

IN

OUT

2.5V 5%, I

= 10A, f = 550kHz. First, calculate

OUT(MAX)

• Place C and C

all in one compact area, close to

OUT

IN

the timing resistor with V = V

:

ON

OUT

the LTC3611. It may help to have some components

2.5V

on the bottom side of the board.

R_ON

=

=187k

(2.4) 550kHz 10pF

)(

(

)

• Keep small-signal components close to the LTC3611.

• Ground connections (including LTC3611 SGND and

PGND) should be made through immediate vias to

the ground plane. Use several larger vias for power

components.

and choose the inductor for about 40% ripple current at

the maximum V :

IN

2.5V

550kHz 0.4 10A

2.5V

36V

ꢁ

ꢂ

ꢄ

ꢅ

L =

1ꢀ

=1μ H

ꢃ

ꢆ

(

)( )(

)

3611fb

17

LTC3611

APPLICATIONS INFORMATION

INTV

CC

V

IN

C

0.1ꢀF

50V

F

C

4.7ꢀF

6.3V

VCC

SW

PGND

SGND

64 63 62 61 60 59 58 57 56 55 54 53 52 51 50 49

1

2

48

47

46

45

44

43

42

41

40

39

38

37

36

35

34

33

PGND

SGND

EXTV

CC

C4

PGND

SW

0.01ꢀF

3

(OPTIONAL)

C2

R1

9.5k

1%

R2

30.1k

1%

V

OUT

4

C1

2.5V AT

10A

L1

1ꢀH

5

C5

22ꢀF

6.3V

C

SW

EXTV

CC

OUT1

(OPTIONAL)

V

OUT

6

100ꢀF

×2

SW

V

FB

R

182k

1%

ON

7

SW

SGND

(OPTIONAL)

8

SW

I

V

IN

GND

ON

LTC3611

9

C

ON

0.01ꢀF

SW

SGND

FCB

(OPTIONAL)

C

C1

680pF

10

11

12

13

14

15

16

R5

12.5k

SW

I

TH

V

IN

V

IN

5V TO 32V

PV

V

RNG

IN

GND

39.2k

R3

PGOOD

+

C

C6

100ꢀF

50V

IN

11k

V

ON

4.7ꢀF

50V

×2

C

C2

100pF

R

PG1

100k

SGND

(OPTIONAL)

R

VON

0Ω

INTV

CC

V

OUT

17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

SGND

SW

2Ω

R

SS1

0.01ꢀF

3611 F06

510k

C

L

= MURATA GRM32ER71H475K

= MURATA GRM43SR60J107M

V

IN

OUT

1

IN

C

SS

0.1ꢀF

INTV

CC

(OPTIONAL)

= COOPER HCP0703-IRO

C

B1

0.22ꢀF

D

B

C5: MURATA GRM31CR60J226KE19

CMDSH-3

KEEP POWER AND SIGNAL GROUNDS SEPARATE.

CONNECT TO ONE POINT.

SW

Figure 6. Design Example: 5V to 32V Input to 2.5V/10A at 550kHz

• Useacompactplanefortheswitchnode(SW)toimprove

cooling of the MOSFETs and to keep EMI down.

• Segregate the signal and power grounds. All small

signal components should return to the SGND pin at

one point, which is then tied to the PGND pin.

• Use planes for V and V

to maintain good voltage

IN

OUT

ﬁltering and to keep power losses low.

• Connect the input capacitor(s) C close to the IC. This

IN

capacitor carries the MOSFET AC current.

• Flood all unused areas on all layers with copper. Flood-

ing with copper reduces the temperature rise of power

components. Connect these copper areas to any DC

• Keep the high dV/dT SW, BOOST and TG nodes away

from sensitive small-signal nodes.

net (V , V , GND or to any other DC rail in your

IN OUT

• Connect the INTV decoupling capacitor C

closely

VCC

CC

system).

to the INTV and PGND pins.

CC

When laying out a printed circuit board without a ground

plane, use the following checklist to ensure proper opera-

tion of the controller. These items are also illustrated in

Figure 7.

• Connect the top driver boost capacitor C closely to

B

the BOOST and SW pins.

• Connect the V pin decoupling capacitor C closely to

IN

F

the V and PGND pins.

IN

3611fb

18

LTC3611

APPLICATIONS INFORMATION

C

VCC

SW

64 63 62 61 60 59 58 57 56 55 54 53 52 51 50 49

1

2

48

47

46

45

44

43

42

41

40

39

38

37

36

35

34

33

PGND

SGND

PGND

SW

3

R1

R2

4

5

SW

EXTV

CC

C

OUT

6

SW

V

FB

7

SW

SGND

R

ON

8

SW

I

ON

LTC3611

V

OUT

9

SW

SGND

FCB

10

11

12

13

14

15

16

C

C1

SW

R

C

SW

I

TH

PV

V

RNG

IN

PGOOD

C

IN

V

ON

SGND

C

C2

17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

D

B

C

SS

B

R

F

3611 F07

Figure 7. LTC3611 Layout Diagram

3611fb

19

LTC3611

TYPICAL APPLICATIONS

3.3V Input to 1.5V/10A at 750kHz

INTV

CC

C

0.1ꢀF

50V

F

C

4.7ꢀF

6.3V

VCC

SW

PGND

SGND

64 63 62 61 60 59 58 57 56 55 54 53 52 51 50 49

1

2

48

47

46

45

44

43

42

41

40

39

38

37

36

35

34

33

PGND

SGND

V

= 5V

IN2

C4

0.01ꢀF

PGND

SW

3

(OPTIONAL)

C2

R2

30.1k

1%

V

OUT

4

R1

20.43k

1%

C1

1.5V AT

10A

L1

0.47ꢀH

5

C5

22ꢀF

6.3V

C

SW

EXTV

CC

OUT1

(OPTIONAL)

V

OUT

6

100ꢀF

×2

SW

V

FB

R

113k

1%

ON

7

SW

SGND

(OPTIONAL)

8

SW

I

V

IN

GND

ON

LTC3611

9

C

ON

0.01ꢀF

SW

SGND

FCB

(OPTIONAL)

C

C1

1500pF

10

11

12

13

14

15

16

R5

12.5k

SW

I

TH

V

IN

V

IN

3.3V

PV

V

RNG

IN

GND

39.2k

PGOOD

11k

+

C

C6

100ꢀF

50V

IN

V

ON

4.7ꢀF

C

C2

100pF

R

PG1

100k

50V

×2

SGND

(OPTIONAL)

INTV

CC

V

OUT

17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

SGND

C

VON

R

3611 TA02

(OPTIONAL)

SS1

510k

C

B1

0.22ꢀF

2Ω

C5: TAIYO YUDEN JMK316BJ226ML-T

V

IN

C

: MURATA GRM31CR71H475K

: MURATA GRM435R60J107M

C

SS

0.1ꢀF

IN

OUT1

(OPTIONAL)

INTV

CC

L1: TOKO FDV0630-R47M

KEEP POWER AND SIGNAL GROUNDS SEPARATE.

CONNECT TO ONE POINT.

3611fb

20

LTC3611

TYPICAL APPLICATIONS

5V to 24V Input to 1.2V/10A at 550kHz

INTV

CC

V

IN

C

0.1ꢀF

50V

F

C

4.7ꢀF

6.3V

VCC

SW

PGND

SGND

64 63 62 61 60 59 58 57 56 55 54 53 52 51 50 49

1

2

48

47

46

45

44

43

42

41

40

39

38

37

36

35

34

33

PGND

SGND

EXTV

CC

C4

PGND

SW

0.01ꢀF

3

(OPTIONAL)

R2

R1

30k

1%

V

OUT

4

C1

30.1k

1%

C2

1.2V AT

10A

L1

0.47ꢀH

5

C5

22ꢀF

6.3V

C

SW

EXTV

CC

OUT1

V

(OPTIONAL)

OUT

IN

6

100ꢀF

×2

SW

V

FB

R

182k

1%

ON

7

SW

SGND

(OPTIONAL)

8

SW

I

V

GND

ON

LTC3611

9

C

ON

0.01ꢀF

SW

SGND

FCB

(OPTIONAL)

C

C1

10

11

12

13

14

15

16

R5

4.75k

1500pF

SW

I

TH

V

IN

V

IN

5V TO 24V

PV

V

RNG

IN

GND

39.2k

PGOOD

11k

+

C

C6

100ꢀF

50V

IN

V

ON

4.7ꢀF

50V

×2

C

C2

100pF

R

PG1

100k

SGND

(OPTIONAL)

INTV

CC

V

OUT

17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

SGND

C

B1

0.22ꢀF

C

VON

R

3611 TA03

(OPTIONAL)

SS1

510k

C5: TAIYO YUDEN JMK316BJ226ML-T

INTV

V

IN

CC

2Ω

C

: MURATA GRM32ER71H475K

: MURATA GRM435R60J167M

C

SS

0.1ꢀF

IN

OUT1

(OPTIONAL)

D

B

CMDSH-3

L1: TOKO HCPO703-OR47

KEEP POWER AND SIGNAL GROUNDS SEPARATE.

CONNECT TO ONE POINT.

3611fb

21

LTC3611

TYPICAL APPLICATIONS

5V to 28V Input to 1.8V/10A All Ceramic 1MHz

INTV

CC

V

IN

C

0.1ꢀF

50V

F

C

4.7ꢀF

6.3V

VCC

SW

PGND

SGND

64 63 62 61 60 59 58 57 56 55 54 53 52 51 50 49

1

2

48

47

46

45

44

43

42

41

40

39

38

37

36

35

34

33

PGND

SGND

EXTV

CC

C4

0.01ꢀF

PGND

SW

3

(OPTIONAL)

C2

R1

10k

1%

R2

20k

1%

V

OUT

C1

4

1.8V AT

10A

47pF

L1

0.68ꢀH

5

C5

22ꢀF

6.3V

C

SW

EXTV

CC

OUT

V

OUT

6

100ꢀF

×2

SW

V

FB

R

102k

1%

ON

7

SW

SGND

(OPTIONAL)

8

SW

I

V

IN

GND

ON

LTC3611

9

C

ON

0.01ꢀF

SW

SGND

FCB

(OPTIONAL)

39.2k

C

C1

680pF

10

11

12

13

14

15

16

R5

12.7k

SW

I

TH

V

IN

V

IN

5V TO 28V

PV

V

RNG

IN

PGOOD

9.31k

C

IN

V

ON

4.7ꢀF

50V

×2

C

C2

100pF

R

PG1

SGND

100k

INTV

CC

V

OUT

17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

SGND

C

B1

0.22ꢀF

C

VON

R

3611 TA04

(OPTIONAL)

SS1

510k

C

: MURATA GRM32ER60J107ME20L

INTV

V

IN

OUT

: MURATA GRM32ER71H475K

CC

2Ω

C

SS

0.1ꢀF

IN

(OPTIONAL)

D

B

L1: VISHAY IHLP2525CZERR68M01

KEEP POWER AND SIGNAL GROUNDS SEPARATE.

CONNECT TO ONE POINT.

CMDSH-3

3611fb

22

LTC3611

PACKAGE DESCRIPTION

WP Package

64-Lead QFN Multipad (9mm × 9mm)

(Reference LTC DWG # 05-08-1812 Rev A)

SEATING PLANE

1.39

3.30

0.50

A

0.00 – 0.05

9.00

BSC

1.19

49 50 51 52 53 54

64

0.20 REF

0.30 – 0.50

B

1.92

48

0.53

(2x)

1

PAD 1

CORNER

2.01

3.06

0.87

3.50

1.17

0.30

(2x)

2.98

3.60

0.95

5

4.53

9.00

BSC

1.30

1.81

4.10

3.30

NX b

3.99

2.04

33

16

WP64 QFN REV A 0707

17

32

0.20 – 0.30

aaa C 2x

TOP VIEW

1.42

3.85

0.90 ± 0.10

NX

// ccc C

0.08 C

BOTTOM VIEW

(BOTTOM METALLIZATION DETAILS)

6

3.30

0.50

1.39

1.19

0.30 – 0.50

PIN1

0.53

(2x)

1.92

0.87

3.50

2.01

NOTE:

1.17

3.06

1. DIMENSIONING AND TOLERANCING CONFORM TO ASME Y14.5M-1994

2. ALL DIMENSIONS ARE IN MILLIMETERS, ANGLES ARE IN DEGREES (°)

3. N IS THE TOTAL NUMBER OF TERMINALS

4. THE LOCATION OF THE TERMINAL #1 IDENTIFIER AND TERMINAL NUMBERING

CONVENTION CONFORMS TO JEDEC PUBLICATION 95 SPP-002

0.30

(2x)

2.98

1.30

0.95

5

6

DIMENSION b APPLIES TO METALLIZED TERMINAL AND IS MEASURED

BETWEEN 0.15mm AND 0.30mm FROM THE TERMINAL TIP.

3.60

4.53

COPLANARITY APPLIES TO THE TERMINALS AND ALL OTHER SURFACE

METALLIZATION

1.81

2.04

4.10

2.30

SYMBOL TOLERANCE

3.30

aaa

bbb

ccc

0.15

0.10

3.99

0.20 – 0.30

3.85

1.42

RECOMMENDED SOLDER PAD LAYOUT

TOP VIEW

3611fb

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.

However,noresponsibilityisassumedforitsuse.LinearTechnologyCorporationmakesnorepresenta-

t ion t h a t t he in ter c onne c t ion o f i t s cir cui t s a s de s cr ib e d her ein w ill no t in fr inge on ex is t ing p a ten t r igh t s.

23

LTC3611

TYPICAL APPLICATION

14V to 32V Input to 12V/5A at 500kHz

C

VCC

4.7ꢀF

6.3V

INTV

V

CC

IN

C

0.1ꢀF

50V

F

SW

PGND

SGND

64 63 62 61 60 59 58 57 56 55 54 53 52 51 50 49

1

2

48

47

46

45

44

43

42

41

40

39

38

37

36

35

34

33

PGND

SGND

EXTV

CC

C4

0.01ꢀF

PGND

SW

3

(OPTIONAL)

C2

R1

1.58k

1%

R2

30.1k

1%

V

OUT

4

C1

12V AT

5A

L1

4.7ꢀH

5

+

C5

22ꢀF

25V

C

SW

EXTV

CC

OUT

(OPTIONAL)

V

OUT

6

180ꢀF

16V

SW

V

FB

R

1M

1%

ON

7

SW

SGND

(OPTIONAL)

8

SW

I

V

IN

GND

ON

LTC3611

9

C

ON

0.01ꢀF

SW

SGND

FCB

(OPTIONAL)

C

C1

560pF

10

11

12

13

14

15

16

R5

20k

SW

I

TH

V

IN

V

IN

14V TO 32V

PV

IN

PV

IN

PV

IN

PV

IN

PV

IN

V

RNG

GND

PGOOD

+

C

C6

100ꢀF

50V

IN

V

4.7ꢀF

50V

×2

ON

C

C2

100pF

R

PG1

SGND

100k

(OPTIONAL)

INTV

CC

I

NTVCC

17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32

SGND

C

R

SS1

B1

0.22ꢀF

C

3611 TA05

(OPTIONAL)

VON

510k

INTV

V

IN

CC

C

: GRM31CR71H475K

IN

C

SS

0.1ꢀF

: SANYO 16SVP180MX

OUT

(OPTIONAL)

D

B

L1: HCP0703-4R7-R

CMDSH-3

RUN/SS

KEEP POWER AND SIGNAL GROUNDS SEPARATE.

CONNECT TO ONE POINT.

RELATED PARTS

PART NUMBER DESCRIPTION

COMMENTS

LTC1778

LTC3411

LTC3412

LTC3414

LTC3418

LTC3610

LTC3770

No R

Current Mode Synchronous Step-Down Controller Up to 97% Efﬁciency, V : 4V to 36V, 0.8V ≤ V

≤ (0.9)(V ),

OUT IN

SENSE

IN

I

Up to 20A

OUT

1.25A (I ), 4MHz, Synchronous Step-Down DC/DC Converter 95% Efﬁciency, V : 2.5V to 5.5V, V : 0.8V, I : 60μA, I : <1μA,

OUT

IN

OUT

Q

SD

MS Package

95% Efﬁciency, V : 2.5V to 5.5V, V

2.5A (I ) 4MHz Synchronous Step-Down DC/DC Converter

: 0.8V, I : 60mA,

Q

OUT

IN

OUT(MIN)

I

: <1mA, TSSOP16E

SD

4A (I ), 4MHz, Synchronous Step-Down DC/DC Converter

95% Efﬁciency, V : 2.25V to 5.5V, V

SD

= 0.8V, I = 64μA,

OUT

IN

OUT(MIN)

Q

I

: <1μA, TSSOP20E Package

8A (I ), 4MHz, Synchronous Step-Down DC/DC Converter

95% Efﬁciency, V : 2.25V to 5.5V, V

= 0.8V, Thermally

OUT

IN

Enhanced 38-Lead QFN Package

12A Current Mode Monolithic Synchronous Step-Down Converter Up to 24V Input (28V Maximum), Current Mode Extremely Fast

Transient Response

Fast, No R

Step-Down Synchronous Controller with

0.67% 0.6V Reference Voltage; Programmable Margining;

True Current Mode; 4V ≤ V ≤ 32V

SENSE

Margining, Tracking, PLL

Low V , No R Synchronous Step-Down Controller

IN

LTC3778

LT3800

0.6V ≤ V

≤ (0.9) V , 4V ≤ V ≤ 36V, I

Up to 20A

OUT

SENSE

OUT

IN

60V Synchronous Step-Down Controller

10A Complete Switch Mode Power Supply

Current Mode, Output Slew Rate Control

92% Efﬁciency, V : 4.5V to 28V, V : 0.6V, True Current Mode

LTM4600HV

IN

OUT

Control, Ultrafast Transient Response

92% Efﬁciency, V : 4.5V to 28V, V : 0.6V, True Current Mode

LTM4601HV

LTM4602HV

LTM4603HV

12A Complete Switch Mode Power Supply

6A Complete Switch Mode Power Supply

IN

OUT

Control, Ultrafast Transient Response

92% Efﬁciency, V : 4.5V to 28V, V : 0.6V, True Current Mode

IN

OUT

Control, Ultrafast Transient Response

93% Efﬁciency, V : 4.5V to 28V, with PLL, Output Tracking and Margining

IN

3611fb

LT 0808 REV B • PRINTED IN USA

LinearTechnology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

24

●

(408) 432-1900 FAX: (408) 434-0507 www.linear.com


型号：	LTC3611IWP-TRPBF
厂家：	Linear
描述：	10A, 32V Monolithic Synchronous Step-Down DC/DC Converter 10A ， 32V单片同步降压型DC / DC转换器转换器
文件：	总24页 (文件大小：397K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

LTC3611IWP-TRPBF [Linear]

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