Rainbow Electronics MAX8737 User Manual

General Description

The MAX8737 dual high-power linear regulator con­trollers 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 exter­nal 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 cur­rent 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 mag­nitude 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
(V

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

V

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

16

1234

12 11 10 9

15

14

13

5

6

7

8

DRV1

GND

N.C.

DRV2

N.C.

CS2

OUT2

REFIN2

CS1

OUT1

REFIN1

PGOOD2

PGOOD1

EN2

EN1

V

CC

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

PIN-PACKAGE

MAX8737ETE

16 Thin QFN-EP* 4mm x 4mm

MAX8737ETE+

16 Thin QFN-EP* 4mm x 4mm

*EP = Exposed pad.

+Denotes lead-free packaging.

TEMP RANGE

-40°C to +85°C

-40°C to +85°C

MAX8737

Dual, Low-Voltage Linear Regulator Controllers
with External MOSFETs

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

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.

VCCto 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 (V

CC

+ 0.3V)

Continuous Power Dissipation (T

A

= +70°C)
16-Pin 4mm x 4mm Thin QFN (derated 25mW/°C

above +70°C).............................................................2000mW

Operating Temperature Range

MAX8737ETE...................................................-40°C to +85°C

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

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

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

ELECTRICAL CHARACTERISTICS

(VCC= 5V, EN_ = CS_ = VCC, V

REFIN

= 1.0V, TA= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)

PARAMETER

CONDITIONS

UNITS

Supply Voltage Range V

CC

V

VCC Undervoltage Lockout
Threshold

Rising edge, 200mV hysteresis (typ) 4.1

4.6 V

VCC Quiescent Supply Current I

CC

EN1 = EN2 = V

CC

0.5 1 mA

VCC Shutdown Supply Current EN1 = EN2 = GND 0.1 5 µA

REFIN to OUT Offset Voltage V

OUT

_-5+5mV

OUT_ Input Bias Current I

OUT

_-1+1µA

DRIVERS

Output high; V

OUT

_ = V

REFIN

_ - 25mV,

I

LOAD

= 1mA

V

CC

-

0.3

VCC -

DRV_ Output Voltage Swing
(Note 1)

Output low; V

OUT

_ = V

REFIN

_ + 25mV,

I

LOAD

= 1mA

0.3

V

DRV_ Maximum Sourcing Current

V

OUT

_ = V

REFIN

_ - 25mV; V

DRV

= 3V 6 14 mA

DRV_ Maximum Sinking Current V

OUT

_ = V

REFIN

_ + 25mV; V

DRV

= 3V 6 14 mA

OUT_ to DRV_ Transconductance
(Large Signal)

0.8 S

DRV_ Power-Supply Rejection
Ratio

10Hz < f < 10kHz, I

DRV

= 1mA, C

DRV

=

10nF

-80 dB

DRV_ Soft-Start Charging Current

I

SOFT

40 170

µA

REFERENCE INPUT

REFIN_ Voltage Range

VCC = 4.75V to 5.5V 0.5 2.5 V

REFIN_ Input Bias Current I

REFIN

_V

REFIN

_ = 0 to 2.5V

-10

nA

FAULT PROTECTION

Thermal Shutdown Threshold T

SHDN

Hysteresis = 20°C

°C

TA = 0°C to +85°C 7 10 13

Current-Limit Threshold V

ILIM

VCS_ - V

OUT

_

T

A

= +85°C 7.5 10

mV

CS_ Input Current -1 +1 µA

Linear Regulator UVP Threshold
(Slow)

(

)

With respect to V

REFIN

; CS_ = V

CC

72 80 88 %

SYMBOL

MIN TYP MAX

4.75 5.50

4.35

0.05

0.03

G

MDRV

V

_

REFIN

-100

+125

UVP

SLOW

400

+100

12.5

MAX8737

Dual, Low-Voltage Linear Regulator Controllers

with External MOSFETs

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(VCC= 5V, EN_ = CS_ = VCC, V

REFIN

= 1.0V, TA= 0°C to +85°C, unless otherwise noted. Typical values are at TA= +25°C.)

PARAMETER

CONDITIONS

UNITS

Linear Regulator UVP Threshold
(Fast)

(

)

With respect to V

REFIN

; CS_ = V

CC

54 60 66 %

Slow Short-Circuit Timer Duration

)

With respect to V

REFIN

; CS_ = V

CC

75 µs

Fast Short-Circuit Timer Duration

)

With respect to V

REFIN

; CS_ = V

CC

5µs

Discharge-Mode On-Resistance
OUT_ Pin

R

OUT

10 Ω

INPUTS AND OUTPUTS

EN_ Input Low Level 0.6 V

EN_ Input High Level Rising edge, 200mV (typ) hysteresis 1.6 V

Enable Leakage Current -1 +1 µA

Power-Good Trip Threshold
(Lower)

With respect to error comparator threshold,
hysteresis = 4% (falling edge)

-15 -12 -9 %

Power-Good Startup Delay 2ms

Power-Good Propagation Delay

OUT_ forced 2% beyond PGOOD_ trip
threshold

1µs

Power-Good Output Low Voltage

I

SINK

= 4mA 0.3 V

V

_ = 1.0V (PGOOD_ high impedance),

ELECTRICAL CHARACTERISTICS

(VCC= 5V, EN_ = CS_ = VCC, V

REFIN

= 1.0V, TA= -40°C to +85°C, unless otherwise noted.) (Note 2)

PARAMETER

SYMBOL

CONDITIONS

MIN

TYP

MAX

UNITS

Supply Voltage Range V

CC

V

VCC Undervoltage Lockout
Threshold

Rising edge 200mV hysteresis (typ) 4.1 4.6 V

VCC Quiescent Supply Current I

CC

EN1 = EN2 = V

CC

1.5 mA

VCC Shutdown Supply Current EN1 = EN2 = GND 5 µA

REFIN to OUT Offset Voltage V

OUT

_-7+7mV

DRIVERS

Output high; V

OUT

_ = V

REFIN

_ - 25mV;

I

LOAD

= 1mA

V

CC

-

0.3

DRV_ Output Voltage Swing
(Note 1)

Output low; V

OUT

_ = V

REFIN

_ + 25mV:

I

LOAD

= 1mA

0.3

V

DRV_ Maximum Sourcing Current

V

OUT

_ = V

REFIN

_ - 25mV; V

DRV

= 3V 3.5 mA

DRV_ Maximum Sinking Current V

OUT

_ = V

REFIN

_ + 25mV; V

DRV

= 3V 3.5 mA

DRV_ Soft-Start Charging Current

I

SOFT

40 400 µA

SYMBOL

UVP

FAST

t

UVP(SLOW

t

UVP(FAST

t

PGOOD

MIN TYP MAX

4.75 5.50

MAX8737

Dual, Low-Voltage Linear Regulator Controllers
with External MOSFETs

4 _______________________________________________________________________________________

ELECTRICAL CHARACTERISTICS (continued)

(VCC= 5V, EN_ = CS_ = VCC, V

REFIN

= 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

VCC = 4.75V to 5.5V 0.5 2.5 V

FAULT PROTECTION

Current-Limit Threshold V

ILIM

VCS_ - V

OUT

_ 6.5

mV

Linear Regulator UVP Threshold
(Slow)

(

)

With respect to V

REFIN

; CS_ = V

CC

72 88 %

Linear Regulator UVP Threshold
(Fast)

(

)

With respect to V

REFIN

; CS_ = V

CC

54 66 %

INPUTS AND OUTPUTS

EN_ Input Low Level 0.6 V

EN_ Input High Level 1.6 V

Power-Good Trip Threshold
(Lower)

With respect to error comparator threshold,
hysteresis = 4% (falling edge)

-15 -9 %

Power-Good Output Low Voltage

I

SINK

= 4mA 0.3 V

Note 1: Low threshold n-channel MOSFET is required for 2.5V (±2%) output.
Note 2: Specifications to -40°C are guaranteed by design, not production tested.

Typical Operating Characteristics

(Circuit of Figure 1, TA = +25°C, unless otherwise noted.)

OUTPUT-VOLTAGE DEVIATION

vs. LOAD CURRENT

MAX8737 toc01

LOAD CURRENT (A)

OUTPUT-VOLTAGE DEVIATION (mV)

1.51.00.5

-4

-3

-2

-1

0

1

2

3

4

5

-5
0 2.0

V

OUT

= 1.5V

FOLDBACK CURRENT LIMIT

vs. OUTPUT VOLTAGE

MAX8737 toc02

OUTPUT VOLTAGE (V)

CURRENT LIMIT (A)

1.00.5

0.4

0.8

1.2

1.6

2.0

2.4

2.8

3.2

0

0 1.5

1ms/div

SOFT-START

(EN RISING EDGE)

5V

3V

C

A

D

MAX8737 toc03

0

0

0

0

1.5V

5V

A. EN1, 5V/div
B. DRV1, 2V/div
NO LOAD

C. LDO1 OUTPUT, 1V/div
D. PGOOD1, 5V/div

B

V

_

REFIN

UVP

SLOW

UVP

FAST

13.5

MAX8737

Dual, Low-Voltage Linear Regulator Controllers

with External MOSFETs

_______________________________________________________________________________________ 5

100µs/div

SOFT-STOP

(EN FALLING EDGE)

5V

3V

C

A

D

MAX8737 toc04

0

0

0

0

1.5V

5V

A. EN1, 5V/div
B. DRV1, 2V/div
NO LOAD

C. LDO1 OUTPUT, 1V/div
D. PGOOD1, 5V/div

B

2ms/div

SOFT-START

(UVLO RISING EDGE)

5V

3V

C

A

D

MAX8737 toc05

0

0

0

0

1.5V

5V

A. 5V BIAS (V

CC

), 5V/div
B. DRV1, 2V/div
NO LOAD, EN = V

CC

C. LDO1 OUTPUT, 1V/div
D. PGOOD1, 5V/div

B

2ms/div

SOFT-STOP

(UVLO FALLING EDGE)

5V

3V

C

A

D

MAX8737 toc06

0

0

0

0

1.5V

5V

A. 5V BIAS (V

CC

), 5V/div
B. DRV1, 2V/div
NO LOAD, EN = V

CC

C. LDO1 OUTPUT, 1V/div
D. PGOOD1, 5V/div

B

10µs/div

LOAD TRANSIENT

(0.1A TO 2.1A)

0

0.1A

C

A

D

MAX8737 toc07

1.50V

1.49V

2.1A

3.2V

2.8V

A. CONTROL SIGNAL
B. LOAD CURRENT, 2A/div

C. DRV1, 500mV/div
D. LDO1 OUTPUT VOLTAGE,
10mV/div

B

1.51V

10µs/div

LOAD TRANSIENT

(NO LOAD TO 2A)

0

0

C

A

D

MAX8737 toc08

1.50V

1.45V

2A

3.2V

2.7V

A. CONTROL SIGNAL
B. LOAD CURRENT, 2A/div

C. DRV1, 1V/div
D. LDO1 OUTPUT VOLTAGE,
50mV/div

B

1.7V

2µs/div

LOAD TRANSIENT

(NO LOAD TO 2A)

0

0

C

A

D

MAX8737 toc09

1.50V

1.45V

2A

3.2V

2.7V

A. CONTROL SIGNAL
B. LOAD CURRENT, 2A/div

C. DRV1, 1V/div
D. LDO1 OUTPUT VOLTAGE,
50mV/div

B

Typical Operating Characteristics (continued)

(Circuit of Figure 1, TA = +25°C, unless otherwise noted.)