MAX8506_技术文档

19-2918; Rev 1; 1/04

PWM Step-Down DC-DC Converters with 75mΩ

Bypass FET for WCDMA and cdmaOne Handsets

General Description

Features

The MAX8506/MAX8507/MAX8508 integrate a PWM step-

down DC-DC regulator and a 75mΩ (typ) bypass FET to

power the PA in WCDMA and cdmaOne™ cell phones.

The supply voltage range is from 2.6V to 5.5V, and the

guaranteed output current is 600mA. One megahertz

PWM switching allows for small external components.

♦ Integrated 75mΩ (typ) Bypass FET

♦ 38mV Dropout at 600mA Load

♦ Up to 94% Efficiency

♦ Dynamically Adjustable Output from 0.4V to 3.4V

(MAX8506, MAX8507)

The MAX8506 and MAX8507 are dynamically controlled

to provide varying output voltages from 0.4V to 3.4V. The

MAX8508 is externally programmed for fixed 0.75V to

3.4V output. Digital logic enables a high-power (HP)

bypass mode that connects the output directly to the bat-

tery for all versions. The MAX8506/MAX8507/MAX8508

are designed so the output settles in less than 30µs for a

full-scale change in output voltage and load current.

♦ Externally Fixed Output from 0.75V to 3.4V

(MAX8508)

♦ 1MHz Fixed-Frequency PWM Switching

♦ 600mA Guaranteed Output Current

♦ Shutdown Mode 0.1µA (typ)

♦ 16-Pin Thin QFN (4mm x 4mm, 0.8mm max Height)

The MAX8506/MAX8507/MAX8508 are offered in 16-pin

4mm x 4mm thin QFN packages (0.8mm max height).

Ordering Information

Applications

WCDMA/NCDMA Cell Phones

PART

TEMP RANGE

-40°C to +85°C

PIN-PACKAGE

16 Thin QFN

Wireless PDAs, Palmtops, and Notebook

Computers

MAX8506ETE

MAX8507ETE

MAX8508ETE

Wireless Modems

Pin Configurations appear at end of data sheet.

cdmaOne is a trademark of CDMA Development Group.

Typical Application Circuits (MAX8506/MAX8507)

OUTPUT

0.4V TO 3.4V OR V

INPUT

2.6V TO 5.5V

4.7µH

BATT

4.7µF

2.2µF

BATTP

LX

BATT

OUT

0.075Ω

MAX8506

MAX8507

SKIP

SHDN

REF

CURRENT-

LIMIT

CONTROL

REF

0.4Ω

0.3Ω

PWM

0.22µF

1MHz

OSC

REFIN

DAC

HP

GND

PGND

COMP

R *

C

C *

f

*

R

C

(kΩ)

10

15

C (pF) C (pF)

C f

MAX8506

MAX8507

1500

1000

100

C *

C

Typical Application Circuits continued at end of data sheet.

________________________________________________________________ Maxim Integrated Products

1

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at

1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

PWM Step-Down DC-DC Converters with 75mΩ

Bypass FET for WCDMA and cdmaOne Handsets

ABSOLUTE MAXIMUM RATINGS

Continuous Power Dissipation (T = +70°C)

A

BATTP, BATT, OUT, SHDN, SKIP, HP, REFIN,

16-Pin Thin QFN (derate 16.9mW/°C above +70°C) ...1.349W

Operating Temperature Range ...........................-40°C to +85°C

Junction Temperature......................................................+150°C

Storage Temperature Range.............................-65°C to +150°C

Lead Temperature (soldering, 10s) .................................+300°C

FB to GND ...........................................................-0.3V to +6V

PGND to GND .......................................................-0.3V to +0.3V

BATT to BATTP......................................................-0.3V to +0.3V

OUT, COMP, REF to GND.......................-0.3V to (V

+ 0.3V)

BATT

LX Current (Note 1)...............................................................1.6A

OUT Current (Note 1)............................................................3.2A

Output Short-Circuit Duration.....................................Continuous

Note 1: LX has internal clamp diodes to PGND and BATT. Applications that forward bias these diodes should take care not to exceed

the IC’s package power-dissipation limits.

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional

operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to

absolute maximum rating conditions for extended periods may affect device reliability.

ELECTRICAL CHARACTERISTICS

(V

= V

= 3.6V, SHDN = SKIP = BATT, HP = GND, V

= 1.932V (MAX8506), V

= 1.70V (MAX8507),

REFIN

BATT

BATTP

REFIN

C

REF

= 0.22µF, T = -40°C to +85°C, unless otherwise noted. Typical values are at T = +25°C.) (Note 2)

A

PARAMETER

CONDITIONS

MIN

2.6

TYP

MAX

5.5

UNITS

Input BATT Voltage

V

Undervoltage Lockout Threshold

Undervoltage Lockout Hysteresis

V

rising

2.150

2.35

40

2.575

BATT

mV

SKIP = GND (normal mode)

SKIP = BATT, 1MHz switching

HP = BATT

180

1750

775

0.1

250

Quiescent Current

µA

Quiescent Current in Dropout

Shutdown Supply Current

1000

5

µA

SHDN = GND

V

= 1.932V, I

= 0.426V, I

= 1.700V, I

= 0.375V, I

= 0 to 600mA (MAX8506)

= 0 to 30mA (MAX8506)

= 0 to 600mA (MAX8507)

= 0 to 30mA (MAX8507)

3.375

0.740

3.375

0.740

250

3.40

0.75

3.40

0.75

485

535

0.1

3.425

0.760

3.425

0.760

REFIN

OUT

OUT Voltage Accuracy

V

MAX8506

MAX8507

OUT Input Resistance

REFIN Input Current

REFIN to OUT Gain

kΩ

µA

275

-1

+1

MAX8506

MAX8507

1.76

2.00

1.25

2.5

V/V

Reference Voltage

1.225

1.275

8.5

V

mV

µF

V

Reference Load Regulation

Reference Bypass Capacitor

FB Voltage Accuracy

FB Input Current

10µA < I

< 100µA

REF

0.1

0.22

0.75

0.03

0.4

FB = COMP (MAX8508)

= 1V (MAX8508)

0.7275

0.7725

0.175

0.825

V

µA

FB

V

= 3.6V

= 2.6V

= 3.6V

= 2.6V

BATT

P-Channel On-Resistance

N-Channel On-Resistance

I

= 180mA

Ω

LX

0.5

0.3

0.5

LX

0.35

HP/Bypass P-Channel

On-Resistance

= 180mA, V

= 3.6V

0.075

0.110

OUT

BATT

2

_______________________________________________________________________________________

PWM Step-Down DC-DC Converters with 75mΩ

Bypass FET for WCDMA and cdmaOne Handsets

ELECTRICAL CHARACTERISTICS (continued)

(V

= V

= 3.6V, SHDN = SKIP = BATT, HP = GND, V

= 1.932V (MAX8506), V

= 1.70V (MAX8507),

REFIN

BATT

BATTP

REFIN

C

REF

= 0.22µF, T = -40°C to +85°C, unless otherwise noted. Typical values are at T = +25°C.) (Note 2)

A

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

P-Channel Current-Limit

Threshold

1.00

1.25

1.50

A

SKIP = BATT (PWM mode)

-0.6

-0.45

0.05

-0.30

0.07

N-Channel Current-Limit

Threshold

A

SKIP = GND (normal mode)

0.03

P-Channel Pulse-Skipping

Current Threshold

SKIP = GND (normal mode)

0.050

0.8

0.125

1.5

0.170

2.5

HP/Bypass P-Channel

Current-Limit Threshold

V

= 3.1V

OUT

LX Leakage Current

OUT Leakage Current

Maximum Duty Cycle

-2

0.01

+2

µA

%

100

SKIP = GND (normal mode)

SKIP = BATT

0

Minimum Duty Cycle

%

12

COMP Clamp Low Voltage

COMP Clamp High Voltage

0.8

2.0

V

MAX8506

MAX8507

MAX8508

85

75

150

130

260

0.48

215

188

376

0.60

Transconductance

µS

V/A

150

0.36

Current-Sense Transresistance

OSCILLATOR

Internal Oscillator Frequency

LOGIC INPUTS (SHDN, HP, SKIP)

Logic-Input High Voltage

Logic-Input Low Voltage

Logic Input Current

0.8

1.6

1

1.2

MHz

V

= 2.6V to 5.5V

V

BATT

0.4

1

0.1

µA

THERMAL SHUTDOWN

Thermal-Shutdown Temperature

Thermal-Shutdown Hysteresis

+160

15

°C

Note 2: Specifications to -40°C are guaranteed by design, not production tested.

_______________________________________________________________________________________

3

PWM Step-Down DC-DC Converters with 75mΩ

Bypass FET for WCDMA and cdmaOne Handsets

Typical Operating Characteristics

(V

BATT

= V

= 3.6V, SHDN = SKIP = BATT, HP = GND, T = +25°C, unless otherwise noted.) (See the Typical Application Circuits.)

BATTP A

EFFICIENCY vs. OUTPUT VOLTAGE

IN NORMAL MODE

EFFICIENCY vs. OUTPUT VOLTAGE

IN PWM MODE

EFFICIENCY vs. INPUT VOLTAGE

100

90

80

70

60

50

100

90

80

70

60

50

R

LOAD

= 15Ω

R

LOAD

= 15Ω

90

80

70

60

50

V

OUT

= 3.4V

R

LOAD

= 10Ω

R

LOAD

= 10Ω

R

LOAD

= 5Ω

R

LOAD

= 5Ω

V

OUT

= 1.2V

V

OUT

= 0.4V

SKIP = GND

R

LOAD

= 10Ω

SKIP = GND

2.5

3.0

3.5

4.0

4.5

5.0

5.5

0

0.5 1.0 1.5 2.0 2.5 3.0 3.5

OUTPUT VOLTAGE (V)

0

0.5 1.0 1.5 2.0 2.5 3.0 3.5

OUTPUT VOLTAGE (V)

INPUT VOLTAGE (V)

SUPPLY CURRENT vs. SUPPLY VOLTAGE

IN PWM MODE

EFFICIENCY vs. LOAD CURRENT

DROPOUT VOLTAGE vs. LOAD CURRENT

100

90

80

70

60

50

150

120

90

60

30

0

6

5

4

3

2

1

0

V

IN

= 3.6V

V

OUT

= 2.5V;

HP = BATT

NORMAL MODE

V

OUT

= 1.2V

V

OUT

= 1.2V;

V

OUT

= 0.4V

PWM

V

OUT

= 2.5V;

PWM

V

OUT

= 1.2V;

NORMAL MODE

1

10

100

1000

0

500

1000

1500

2000

2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5

SUPPLY VOLTAGE (V)

LOAD CURRENT (mA)

SUPPLY CURRENT vs. SUPPLY VOLTAGE

IN NORMAL MODE

HEAVY-LOAD SWITCHING WAVEFORM

MAX8506 toc08

1000

900

800

700

600

500

400

300

200

100

SKIP = GND

V

LX

2V/div

V

OUT

= 3.4V

V

OUT

AC-COUPLED

20mV/div

V

OUT

= 1.2V

V

OUT

= 0.4V

V

OUT

= 1.2V

LOAD = 10Ω

2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5

SUPPLY VOLTAGE (V)

1µs/div

4

_______________________________________________________________________________________

PWM Step-Down DC-DC Converters with 75mΩ

Bypass FET for WCDMA and cdmaOne Handsets

Typical Operating Characteristics (continued)

(V

BATT

= V

= 3.6V, SHDN = SKIP = BATT, HP = GND, T = +25°C, unless otherwise noted.) (See the Typical Application Circuits.)

BATTP A

LIGHT-LOAD SWITCHING WAVEFORM

IN PWM MODE

IN NORMAL MODE

MAX8506 toc09

MAX8506 toc10

V

LX

V

LX

2V/div

V

OUT

V

OUT

AC-COUPLED

5mV/div

AC-COUPLED

20mV/div

V

OUT

= 0.4V

V

OUT

= 0.4V

LOAD = 10Ω, SKIP = GND

LOAD = 10Ω

1µs/div

400µs/div

EXITING AND ENTERING SHUTDOWN

REFIN TRANSIENT RESPONSE

MAX8506 toc11

MAX8506 toc12

REFIN

1V/div

SHDN

2V/div

0

SKIP = GND

V

OUT

V

1V/div

OUT

1V/div

SKIP = BATT

= 0.284V TO 1.420V

V

REFIN

V

OUT

= 1.8V, R

= 10Ω

LOAD

100µs/div

20µs/div

LINE TRANSIENT RESPONSE

HP TRANSIENT RESPONSE

MAX8506 toc14

MAX8506 toc13

HP

1V/div

V

IN

200mV/div

0

3.4V

SKIP = GND

V

OUT

V

OUT

1V/div

AC-COUPLED

20mV/div

SKIP = BATT

= 10Ω

1.8V

V

OUT

= 1.2V, R

= 10Ω

LOAD

V

OUT

= 1.8V, R

LOAD

20µs/div

_______________________________________________________________________________________

5

PWM Step-Down DC-DC Converters with 75mΩ

Bypass FET for WCDMA and cdmaOne Handsets

Pin Description

NAME

FUNCTION

MAX8506

MAX8507

MAX8508

Shutdown Control Input. Drive low for shutdown mode. Connect to BATT or logic high to

enable the IC.

1

2

3

1

2

3

SHDN

GND

REF

Ground. Connect to PGND and directly to EP.

Reference Output. Output of the internal 1.25V reference. Bypass to GND with a 0.22µF

capacitor.

External Reference Input. Connect to the output of a digital-to-analog converter for

dynamic adjustment of the output voltage.

4

5

—

5

REFIN

COMP

Compensation. Connect a compensation network from COMP to GND to stabilize the

regulator. See the Typical Application Circuits.

High-Power Bypass Control Input. Drive low for OUT to regulate to the voltage set by

REFIN (MAX8506/MAX8507) or the external resistors on FB (MAX8508). Drive HP high for

OUT to be connected to BATT by an internal bypass PFET.

6

HP

7

8

7

8

N.C.

No Connection. Connect to PGND.

Power Ground. Connect to GND.

PGND

Inductor Connection to the Drains of the Internal Power MOSFETs. LX is high impedance

in shutdown mode.

9

LX

Supply Voltage Input. Connect to a 2.6V to 5.5V source. Bypass BATTP to PGND with a

low-ESR 2.2µF capacitor. Connect BATTP to BATT.

10

BATTP

11, 13, 15

12, 14

11, 13, 15

12, 14

BATT

OUT

Supply Voltage Input. Connect all BATT pins to BATTP.

Regulator Output. Connect both OUT pins directly to the output voltage.

Skip Control Input. Connect to GND or drive low to enable pulse skipping under light

loads. Connect SKIP to BATT or logic high for forced-PWM mode.

16

SKIP

Output Feedback Sense Input. To set the output voltage, connect FB to the center of an

external resistive voltage-divider between OUT and GND. FB voltage regulates to 0.75V

when HP is low.

—

4

FB

EP

—

Exposed Pad. Connect directly to GND underneath the IC.

ponent size. Each device includes an internal synchro-

Detailed Description

nous rectifier for high efficiency, which eliminates the

need for an external Schottky diode. The normal operat-

ing mode uses constant-frequency PWM switching at

medium and heavy loads and automatically pulse skips

at light loads to reduce supply current and extend bat-

tery life. A forced-PWM mode switches at a constant

frequency, regardless of load, to provide a well-con-

trolled spectrum in noise-sensitive applications. Battery

life is maximized by the low-dropout (75mΩ) high-

power mode and a 0.1µA (typ) logic-controlled shut-

down mode.

The MAX8506/MAX8507/MAX8508 PWM step-down DC-

DC converters with integrated bypass PFET are opti-

mized for low-voltage, battery-powered applications

where high efficiency and small size are priorities. An

analog control signal dynamically adjusts the MAX8506/

MAX8507s’ output voltage from 0.4V to 3.4V with a set-

tling time of 30µs. The MAX8508 uses external feedback

resistors to set the output voltage from 0.75V to 3.4V.

The MAX8506/MAX8507/MAX8508 operate at a high

1MHz switching frequency that reduces external com-

6

_______________________________________________________________________________________

PWM Step-Down DC-DC Converters with 75mΩ

Bypass FET for WCDMA and cdmaOne Handsets

Then the main switch turns off and the magnetic field in

the inductor collapses while current flows through the

synchronous rectifier to the output filter capacitor and

the load. The synchronous rectifier is turned off when

the inductor current reaches zero. The MAX8506/

MAX8507/MAX8508 wait until the skip comparator

senses a low output voltage again.

PWM Control

The MAX8506/MAX8507/MAX8508 use a fixed-frequen-

cy, current-mode and PWM controller capable of achiev-

ing 100% duty cycle. Current-mode feedback provides

cycle-by-cycle current limiting and superior load and line

response, as well as overcurrent protection for the inter-

nal MOSFET and rectifier. A comparator at the P-channel

MOSFET switch detects overcurrent at 1.25A.

Forced-PWM Operation

Connect SKIP to BATT for forced-PWM operation.

Forced-PWM operation is desirable in sensitive RF and

data-acquisition applications to ensure that switching

harmonics do not interfere with sensitive IF and data-

sampling frequencies. A minimum load is not required

during forced-PWM operation since the synchronous

rectifier passes reverse-inductor current as needed to

allow constant-frequency operation with no load. Forced-

PWM operation uses higher supply current with no load

(1.75mA typ) compared to skip mode (180µA typ).

During PWM operation, the MAX8506/MAX8507/

MAX8508 regulate the output voltage by switching at a

constant frequency and then modulating the duty cycle

with PWM control. The error-amp output, the main

switch current-sense signal, and the slope-compensa-

tion ramp are all summed using a PWM comparator.

The comparator modulates the output power by adjust-

ing the peak inductor current during the first half of

each cycle based on the output-error voltage. The

MAX8506/MAX8507/MAX8508 have relatively low AC

loop gain coupled with a high-gain integrator to enable

the use of a small and low-valued output filter capaci-

tor. The resulting load regulation is 0.1% at 0 to 600mA.

100% Duty-Cycle Operation and Dropout

The maximum on-time can exceed one internal oscilla-

tor cycle, which permits operation at 100% duty cycle.

Near dropout, cycles can be skipped, reducing switch-

ing frequency. However, voltage ripple remains small

because the current ripple is still low. As the input volt-

age drops even further, the duty cycle increases until

the internal P-channel MOSFET stays on continuously.

Dropout voltage at 100% duty cycle is the output cur-

rent multiplied by the sum of the internal PMOS on-

resistance (400mΩ typ) and the inductor resistance.

For lower dropout, use the high-power bypass mode

(75mΩ typ).

Normal-Mode Operation

Connecting SKIP to GND enables normal operation. This

allows automatic PWM control at medium and heavy

loads and skip mode at light loads to improve efficiency

and reduce quiescent current to 180µA. Operating in

normal mode allows the MAX8506/MAX8507/MAX8508

to pulse skip when the peak inductor current drops

below 90mA. During skip operation, the MAX8506/

MAX8507/MAX8508 switch only as needed to service

the load, reducing the switching frequency and associat-

ed losses in the internal switch and synchronous rectifier.

High-Power Bypass Mode

A high-power bypass mode is available for use when a

PA transmits at high power. This mode connects OUT

to BATT through the bypass PFET. Additionally, the

PWM buck converter is forced into 100% duty cycle to

further reduce dropout. The dropout in the bypass

PFET equals the load current multiplied by the on-resis-

tance (75Ω typ) in parallel with the buck converter and

inductor dropout resistance.

There are three steady-state operating conditions for

the MAX8506/MAX8507/MAX8508 in normal mode:

1) The device performs in continuous conduction for

heavy loads in a manner identical to forced-PWM

mode. 2) The inductor current becomes discontinuous

at medium loads, requiring the synchronous rectifier to

be turned off before the end of a cycle as the inductor

current reaches zero. 3) The device enters into skip

mode when the converter output voltage exceeds its

regulation limit before the inductor current reaches its

skip threshold level.

Undervoltage Lockout (UVLO)

The MAX8506/MAX8507/MAX8508 do not operate with

battery voltages below the UVLO threshold of 2.35V

(typ). The output remains off until the supply voltage

exceeds the UVLO threshold. This guarantees the

integrity of the output voltage regulation.

During skip mode, a switching cycle initiates when the

output voltage has dropped out of regulation. The P-

channel MOSFET switch turns on and conducts current

to the output-filter capacitor and load until the inductor

current reaches the pulse-skipping current threshold.

_______________________________________________________________________________________

7

PWM Step-Down DC-DC Converters with 75mΩ

Bypass FET for WCDMA and cdmaOne Handsets

The MAX8506/MAX8507s’ output voltage is dynamically

adjustable from 0.4V to 3.4V by the use of the REFIN

Synchronous Rectification

An N-channel synchronous rectifier operates during the

second half of each switching cycle (off-time). When

the inductor current falls below the N-channel current-

comparator threshold or when the PWM reaches the

end of the oscillator period, the synchronous rectifier

turns off. This prevents reverse current from the output

to the input in pulse-skipping mode. During PWM oper-

ation, the NEGLIM threshold adjusts to permit reverse

current during light loads. This allows regulation with a

constant switching frequency and eliminates minimum

load requirements for fixed-frequency operation.

input. The gain from V

to V

is internally set to

REFIN

OUT

1.76 (MAX8506) or 2.00 (MAX8507). V

can be adjust-

OUT

ed during operation by driving REFIN with an external

DAC. The MAX8506/MAX8507 output responds to full-

scale change in voltage and current in less than 30µs.

Using External Divider (MAX8508)

The MAX8508 is intended for two-step V

control

CC

applications where high efficiency is a priority. Select

an output voltage between 0.75V and 3.4V by connect-

ing FB to a resistive-divider between the output and

GND (see the MAX8508 Typical Application Circuit).

Select feedback resistor R2 in the 5kΩ to 50kΩ range.

R1 is then given by:

Shutdown Mode

Drive SHDN to GND to place the MAX8506/MAX8507/

MAX8508 in shutdown mode. In shutdown, the refer-

ence, control circuitry, internal switching MOSFET, and

synchronous rectifier turn off and the output becomes

high impedance. Input current falls to 0.1µA (typ) dur-

ing shutdown mode. Drive SHDN high to enable the IC.





V

OUT

R1 = R2 ×

−1









FB

where V = 0.75V.

FB

Current-Sense Comparators

The MAX8506/MAX8507/MAX8508 use several internal

current-sense comparators. In PWM operation, the PWM

comparator terminates the cycle-by-cycle on-time and

provides improved load and line response. A second cur-

rent-sense comparator used across the P-channel switch

controls entry into skip mode. A third current-sense com-

parator monitors current through the internal N-channel

MOSFET to prevent excessive reverse currents and

determine when to turn off the synchronous rectifier. A

fourth comparator used at the P-channel MOSFET

detects overcurrent. A fifth comparator used at the

bypass P-channel MOSFET detects overcurrent in the

HP mode or at dropout. This protects the system, exter-

nal components, and internal MOSFETs under overload

conditions.

Input Capacitor Selection

Capacitor ESR is a major contributor to input ripple in

high-frequency DC-DC converters. Ordinary aluminum-

electrolytic capacitors have high ESR and should be

avoided. Low-ESR tantalum or polymer capacitors are

better and provide a compact solution for space-con-

strained surface-mount designs. Ceramic capacitors

have the lowest overall ESR.

The input filter capacitor reduces peak currents and

noise at the input voltage source. Connect a low-ESR

bulk capacitor (2.2µF to 10µF) to the input. Select this

bulk capacitor to meet the input ripple requirements

and voltage rating rather than capacitance value. Use

the following equation to calculate the maximum RMS

input current:

Applications Information

I

OUT

I

=

× V

×(V − V

)

Setting the Output Voltage

RMS

OUT

IN

OUT

V

IN

Using a DAC (MAX8506/MAX8507)

The MAX8506/MAX8507 are optimized for highest sys-

tem efficiency when applying power to a linear PA in

CDMA handsets. When transmitting at less than full

power, the supply voltage to the PA is lowered in many

steps from 3.4V to as low as 0.4V to greatly reduce bat-

tery current (see the Typical Application Circuits). The

use of DC-DC converters such as the MAX8506/

MAX8507 dramatically extends talk time in these appli-

cations.

Compensation, Stability, and

Output Capacitor

The MAX8506/MAX8507/MAX8508 are externally com-

pensated by placing a resistor and a capacitor (see the

Typical Application Circuits, R and C ) in series from

C

COMP to GND. An additional capacitor (C ) may be

f

required from COMP to GND if high-ESR output capaci-

tors are used. The C capacitor integrates the current

C

from the transimpedance amplifier, averaging output

8

_______________________________________________________________________________________

PWM Step-Down DC-DC Converters with 75mΩ

Bypass FET for WCDMA and cdmaOne Handsets

Table 1. Suggested Inductors

PART

NUMBER

INDUCTANCE

(µH)

SATURATION

CURRENT (A)

SUPPLIER

ESR (mΩ)

DIMENSIONS (mm)

Murata

LQH32C-53

CDRH2D11

LBLQ2016

D312C

4.7

150

135

250

200

0.650

0.500

0.210

0.790

2.5 x 3.2 x 1.7

3.2 x 3.2 x 1.2

1.6 x 2.0 x 1.6

3.6 x 3.6 x 1.2

Sumida

Taiyo Yuden

TOKO

capacitor ripple. This sets the device speed for transient

response and allows the use of small ceramic output

capacitors because the phase-shifted capacitor ripple

does not disturb the current-regulation loop. The resistor

sets the proportional gain of the output error voltage by

PC Board Layout and Routing

Table 2. Component Suppliers

SUPPLIER

PHONE

WEBSITE

Murata

770-436-1300

847-956-0666

408-573-4150

847-297-0070

www.murata.com

www.sumida.com

www.t-yuden.com

www.tokoam.com

a factor of g x R . Increasing this resistor also increas-

m

C

Sumida

es the sensitivity of the control loop to output ripple.

Taiyo Yuden

TOKO

The resistor and capacitor set a compensation zero that

defines the system’s transient response. The load cre-

ates a dynamic pole, shifting in frequency with changes

in load. As the load decreases, the pole frequency

shifts to the left. System stability requires that the com-

pensation zero must be placed to ensure adequate

phase margin (at least 30° at unity gain). With a 4.7µF

High switching frequencies and large peak currents

make PC board layout a very important part of design.

Good design minimizes EMI, noise on the feedback

paths, and voltage gradients in the ground plane, all of

which can result in instability or regulation errors.

Connect the inductor, input filter capacitor, and output fil-

ter capacitor as close together as possible and keep their

traces short, direct, and wide. The external voltage- feed-

back network should be very close to the FB pin, within

0.2in (5mm). Keep noisy traces, such as those from the

LX pin, away from the voltage-feedback network. Position

the bypass capacitors as close as possible to their

respective supply and ground pins to minimize noise cou-

pling. For optimum performance, place input and output

capacitors as close to the device as possible. Connect

GND directly under the IC to the exposed paddle. Refer

to the MAX8506 evaluation kit for an example PC board

layout and routing scheme.

output capacitor, the recommended C and R for the

C

MAX8506 are 1500pF and 10kΩ, respectively. This pro-

vides adequate phase margin over the entire output

voltage and load range and optimizes the output-

voltage settling time for REFIN dynamic control. See the

Typical Application Circuits for recommended C and

C

R values for the MAX8507 and MAX8508.

C

Inductor Selection

A 4µH to 6µH inductor is recommended for most appli-

cations. For best efficiency, the inductor’s DC resistance

should be <400mΩ. Saturation current (I

) should be

SAT

greater than the maximum DC load at the PA’s supply

plus half the inductor current ripple. Two-step V

CC

applications typically require very small inductors with

in the 200mA to 300mA region. See Tables 1 and 2

I

SAT

for recommended inductors and suppliers.

_______________________________________________________________________________________

9

PWM Step-Down DC-DC Converters with 75mΩ

Bypass FET for WCDMA and cdmaOne Handsets

Typical Application Circuits (MAX8508) (continued)

OUTPUT

0.75V TO 3.4V OR V

INPUT

2.6V TO 5.5V

4.7µH

BATT

4.7µF

2.2µF

BATTP

LX

BATT

OUT

MAX8508

0.075Ω

SKIP

SHDN

0.4Ω

0.3Ω

REF

CURRENT-

LIMIT

CONTROL

REF

PWM

0.22µF

R1

R2

1MHz

OSC

FB

HP

0.75V

PGND

GND

COMP

R

C

5.6kΩ

C

f

2700pF

100pF

Pin Configurations

TOP VIEW

16 15 14 13

SHDN

GND

1

2

3

4

SHDN

GND

REF

1

2

3

4

12 OUT

11 BATT

10 BATTP

11 BATT

10 BATTP

MAX8506

MAX8507

MAX8508

REF

REFIN

9

LX

FB

9

LX

5

6

7

8

5

6

7

8

THIN QFN

4mm x 4mm

THIN QFN

4mm x 4mm

Chip Information

TRANSISTOR COUNT: 2020

PROCESS: BiCMOS

10 ______________________________________________________________________________________

PWM Step-Down DC-DC Converters with 75mΩ

Bypass FET for WCDMA and cdmaOne Handsets

Package Information

(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,

go to www.maxim-ic.com/packages.)

PACKAGE OUTLINE

12,16,20,24L QFN THIN, 4x4x0.8 mm

1

21-0139

B

2

PACKAGE OUTLINE

12,16,20,24L QFN THIN, 4x4x0.8 mm

2

21-0139

B

2

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are

implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 11

Printed USA

is a registered trademark of Maxim Integrated Products.

This datasheet has been download from:

www.datasheetcatalog.com

Datasheets for electronics components.


型号：	MAX8506
厂家：	MAXIM INTEGRATED PRODUCTS
描述：	PWM Step-Down DC-DC Converters with 75m? Bypass FET for WCDMA and cdmaOne Handsets PWM降压型75mΩ旁路FET的DC -DC转换器，用于WCDMA和cdmaOne手机转换器 CD 手机
文件：	总12页 (文件大小：385K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

MAX8506 [MAXIM]

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MAX8506ETE+T

MAX8506EVKIT

MAX8506|MAX8507|MAX8508

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MAX8507ETE

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MAX8508ETE

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MAX8508ETE+T

MAX8508ETE-T