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General Description

The MAX8737 dual high-power linear regulator con-

trollers use external n-channel MOSFETs to generate

two independent low-voltage supplies for notebook

computers. The MAX8737 delivers low output voltages

from 0.5V to 2.5V (±5mV no-load accuracy). The exter-

nal components allow scalable current design with

loads up to 5A with excellent load regulation (1%). The

regulator operates from a low input voltage, which also

reduces the power dissipation in the external n-channel

MOSFET. The controller powers the external MOSFET

gate driver from the standard 5V system supply.

The MAX8737 includes current and thermal limits to

prevent damage to the linear regulator. The MAX8737

uses an external resistive divider to fold back the cur-

rent limit, reducing the overall power dissipation. The

MAX8737 uses an external resistive-divider in series

with the current-sense input (CS_), providing foldback

current-limit protection, and effectively reducing the

short-circuit power dissipation.

An output undervoltage timeout is available for low-cost

applications that omit the current-sense resistor. The

output undervoltage (UVP) timing depends on the mag-

nitude of the voltage at V

OUT

. The UVP detects and

shuts down the LDO if the output voltage drops out of

regulation. The controller uses an adjustable reference

input (REFIN_) to set the nominal output voltage

OUT_

), which minimizes the cost and makes the sta-

bility independent of the output voltage.

Each linear regulator features an adjustable soft-start

function, and generates a delayed power-good

(PGOOD) signal that signals when the linear regulator

is in regulation. The MAX8737 is a low-cost solution

requiring few external components and is available in a

small, 4mm x 4mm, 16-pin thin QFN package.

Applications

Notebook and Desktop Computers

Point-of-Load Regulators

MCH

and V

CCP

CPU Supplies

Low-Voltage Bias Supplies

Servers

Features

♦ Low-Cost Dual Linear Regulators

♦ Output Voltage Accuracy ±5mV

♦ Independent 0.5V to 2.5V Reference Inputs

♦ Foldback Current-Limit Protection

♦ Output Undervoltage-Lockout Protection

♦ Thermal Limit (Internal Sensor)

♦ 1.0V to 5.5V Input Supply Voltage (External FET

Drain)

♦ 5V Bias Supply Voltage

♦ Independent Power-Good Open-Drain Outputs

♦ Independent Enable Inputs

♦ Soft-Shutdown Output Discharge

♦ Low Supply Current (0.5mA)

♦ 5µA (max) Shutdown Supply Current

MAX8737

Dual, Low-Voltage Linear Regulator Controllers

with External MOSFETs

________________________________________________________________ Maxim Integrated Products 1

1234

12 11 10 9

DRV1

GND

N.C.

DRV2

N.C.

CS2

OUT2

REFIN2

CS1

OUT1

REFIN1

PGOOD2

PGOOD1

EN2

EN1

TOP VIEW

MAX8737

4mm x 4mm TQFN

Pin Configuration

19-3705; Rev 0; 5/05

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.

EVALUATION KIT

AVAILABLE

Ordering Information

PART

TEMP RANGE

PIN-PACKAGE

MAX8737ETE

-40°C to +85°C

16 Thin QFN-EP* 4mm x 4mm

MAX8737ETE+

-40°C to +85°C

16 Thin QFN-EP* 4mm x 4mm

*EP = Exposed pad.

+Denotes lead-free packaging.

Summary of content (15 pages)

PAGE 1
9-3705; Rev 0; 5/05 KIT ATION EVALU E L B AVAILA Dual, Low-Voltage Linear Regulator Controllers with External MOSFETs ♦ Low-Cost Dual Linear Regulators ♦ Output Voltage Accuracy ±5mV ♦ Independent 0.5V to 2.5V Reference Inputs ♦ Foldback Current-Limit Protection ♦ Output Undervoltage-Lockout Protection ♦ Thermal Limit (Internal Sensor) ♦ 1.0V to 5.
PAGE 2
MAX8737 Dual, Low-Voltage Linear Regulator Controllers with External MOSFETs ABSOLUTE MAXIMUM RATINGS VCC to GND ..............................................................-0.3V to +6V OUT1, OUT2 to GND................................................-0.3V to +6V REFIN1, REFIN2, PGOOD1, PGOOD2, EN1, EN2 to GND..........................................................-0.3V to +6V DRV1, DRV2, CS1, CS2 to GND.................-0.3V to (VCC + 0.
PAGE 3
Dual, Low-Voltage Linear Regulator Controllers with External MOSFETs (VCC = 5V, EN_ = CS_ = VCC, VREFIN = 1.0V, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.
PAGE 4
ELECTRICAL CHARACTERISTICS (continued) (VCC = 5V, EN_ = CS_ = VCC, VREFIN = 1.0V, TA = -40°C to +85°C, unless otherwise noted.) (Note 2) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS REFERENCE INPUT REFIN_ Voltage Range VREFIN_ VCC = 4.75V to 5.5V 0.5 2.5 V VCS_ - VOUT_ 6.5 13.5 mV FAULT PROTECTION Current-Limit Threshold VILIM Linear Regulator UVP Threshold (Slow) UVP(SLOW) With respect to VREFIN; CS_ = VCC 72 88 % Linear Regulator UVP Threshold (Fast) UVP(FAST) 54 66 % 0.
PAGE 5
Dual, Low-Voltage Linear Regulator Controllers with External MOSFETs SOFT-STOP (EN FALLING EDGE) SOFT-START (UVLO RISING EDGE) MAX8737 toc04 5V SOFT-STOP (UVLO FALLING EDGE) MAX8737 toc05 A 0 5V MAX8737 toc06 A 0 3V 3V 3V B 0 1.5V C 0 5V D 0 D 2ms/div A 0 2A B 0 0.1A MAX8737 toc09 A 2.1A B 2.7V C 1.7V 1.51V D 1.50V A 0 2A B 0 3.2V C C. LDO1 OUTPUT, 1V/div D. PGOOD1, 5V/div LOAD TRANSIENT (NO LOAD TO 2A) MAX8737 toc08 MAX8737 toc07 3.2V 2.8V A. 5V BIAS (VCC), 5V/div B.
PAGE 6
Typical Operating Characteristics (continued) (Circuit of Figure 1, TA = +25°C, unless otherwise noted.) MAX8737 toc10 50 OUT1 OUT2 A 0 C 0 1.50V D 20 10 0 -5 0 5 3 7.5 20 10 MAX8737 toc14 2 1.3 60 40 20 -20 0 180 -1 90 0 -2 -90 -180 -3 1.0 1.5 -40 -15 10 TRANSCONDUCTANCE (S) 35 85 60 TEMPERATURE (°C) 0.001 0.01 0.1 MAX8737 toc16 GAIN (dB) 40 20 0 -20 180 PHASE (°) 90 0 -90 -180 0.01 0.1 10 1.5V OUTPUT, 1A LOAD, COUT = (1) 10µF 1206 16V CERAMIC 60 0.
PAGE 7
Dual, Low-Voltage Linear Regulator Controllers with External MOSFETs PIN NAME FUNCTION 1 VCC Analog and Driver Supply Input. Connect to the system supply voltage (+5.0V). Bypass VCC to analog ground with a 1µF or greater ceramic capacitor. 2 CS1 Positive Current-Sense Input for LDO1. To enable (foldback) current limit, connect CS1 to the positive terminal of the current-sense element as shown in Figure 1.
PAGE 8
MAX8737 Dual, Low-Voltage Linear Regulator Controllers with External MOSFETs Detailed Description The MAX8737 is a dual, low-dropout, external n-channel linear regulator controller for low-voltage notebook computer power supplies. The linear regulator provides a 0.5V to 2.5V (±5mV no-load) output for powering the low-voltage supplies to desktop and notebook CPU chipsets (VCCP and VCC_MCH).
PAGE 9
Dual, Low-Voltage Linear Regulator Controllers with External MOSFETs N1/N2: Si 4922DY C1 1.0µF VCC R6A 100kΩ R6B 100kΩ POWER GOOD 1 1.5V 2A (MAX) N1 CIN1 10µF MAX8737 N2 DRV1 RCS1 20mΩ R4A 10Ω CIN2 10µF DRV2 R3A 27Ω COUT1 10µF POWER GOOD 2 PGOOD2 PGOOD1 INPUT 1.8V TO 2.5V CSYS1* 100µF MAX8737 5V BIAS SUPPLY INPUT 1.25V TO 1.5V CSYS2* 100µF R3B 33Ω C2A 0.1µF C2B 0.22µF R4B 10Ω CS1 1.05V 3A (MAX) RCS2 20mΩ COUT2 22µF CS2 R5A 340Ω R5B 150Ω OUT1 OUT2 ON ON EN2 EN1 OFF R1A 33.
PAGE 10
MAX8737 Dual, Low-Voltage Linear Regulator Controllers with External MOSFETs RCS N1 INPUT 1.0V TO 5.5V OUTPUT COUT 4.7µF/A CIN R3 OUT CS DRV C2 0.4V C1 MAX8737 ERROR AMPLIFIER R6 PGOOD REF R2 DELAY LOGIC 88% ILIM_EN 75µs DELAY S Q 80% R EN 60% GND THE MAX8737 INCLUDES TWO LDOs AS SHOWN ABOVE. Figure 2.
PAGE 11
Dual, Low-Voltage Linear Regulator Controllers with External MOSFETs MAX8737 INPUT INPUT MAX8737 MAX8737 CIN DRV CIN DRV R3 R3 VOUT RCS C2 VOUT COUT RCS C2 R1 COUT CS CS OUT R2 OUT IMAX IMAX 10mV RCS 10mV RCS VOUT SIMPLE CURRENT-LIMIT PROTECTION VOUT FOLDBACK CURRENT-LIMIT PROTECTION Figure 3. Current-Limit Protection Slow UVP If the output drops below 80% of the nominal output voltage (VREFIN) for 75µs, the MAX8737 shuts down the LDO and pulls the DRV_ pin to ground.
PAGE 12
MAX8737 Dual, Low-Voltage Linear Regulator Controllers with External MOSFETs provide good transient response, the capacitor’s ESR should be minimized: ∆VOUT = ∆IOUT x ESR where ∆IOUT is the maximum peak-to-peak load current step, and ∆VOUT is the transient output-voltage tolerance. Example: The example below is used to demonstrate the stability calculation for the application circuit in Figure 1. 1) Choose VOUT = 1.
PAGE 13
Dual, Low-Voltage Linear Regulator Controllers with External MOSFETs VIN _ MIN − VOUT _ MAX ≥ IMAX (RDSON _ MAX + RCS ) where VIN_MIN is the minimum input voltage at the drain of the MOSFET. MOSFET Power Dissipation The maximum power dissipation of the MAX8737 depends on the thermal resistance of the external nchannel MOSFET package, the board layout, the temperature difference between the die and ambient air, and the rate of airflow.
PAGE 14
MAX8737 Dual, Low-Voltage Linear Regulator Controllers with External MOSFETs N1/N2: Si 4922DY 5V BIAS SUPPLY C1 1.0µF *A LOCAL 10µF CERAMIC CAPACITOR IS SUFFICIENT FOR MOST APPLICATIONS. IF THE MAX8737 IS POWERED FROM A HIGH-IMPEDANCE SOURCE, ADDITIONAL LOW-ESR POLYMER CAPACITORS ARE RECOMMENDED ON THE INPUT. VCC CS2 CS1 R6A 100kΩ POWER GOOD 1 R6B 100kΩ PGOOD1 INPUT 1.8V TO 2.5V POWER GOOD 2 PGOOD2 INPUT 1.25V TO 1.5V CSYS2* 100µF MAX8737 CIN1 10µF CSYS1* 100µF 1.
PAGE 15
Dual, Low-Voltage Linear Regulator Controllers with External MOSFETs 24L QFN THIN.EPS PACKAGE OUTLINE, 12, 16, 20, 24, 28L THIN QFN, 4x4x0.8mm 21-0139 D 1 2 PACKAGE OUTLINE, 12, 16, 20, 24, 28L THIN QFN, 4x4x0.8mm 21-0139 D 2 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.