May 1998

ML4902

High Current Synchronous Buck Controller

1

GENERAL DESCRIPTION

The ML4902 high current synchronous buck controller

provides high efficiency DC/DC conversion to generate

The ML4902 controller, when combined with 2 N-channel

MOSFETs, generates output voltages between 1.8V and

3.5V from a 5V supply. The output voltage is selected via

an internal 2 chord 4-bit DAC. In the upper range, the

output can be set between 2.1V and 3.5V in 100mV steps.

In the lower range, the output can be set between 1.8V

and 2.05V in 50mV steps. Output currents in excess of

20A can be attained at efficiencies greater than 90%.

The ML4902 can be enabled/disabled via the SHDN pin.

While disabled, the output of the regulator is completely

isolated from the circuit’s input supply. The ML4902

employs fixed-frequency PWM control combined with a

sophisticated control loop enhancement circuit to provide

excellent load transient response.

FEATURES

s

Designed to meet Pentium Pro and Pentium II VRM

power supply requirements

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DC regulation to +1% maximum

s

Proprietary circuitry provides transient response of ±5%

maximum over a 0A to 20A load range

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Programmable output voltage (1.8V to 3.5V) is set by

an onboard 2 chord 4-bit DAC

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Synchronous N-channel buck topology for maximum

power conversion efficiency

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Fixed frequency operation for easier system integration

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Integrated anti-shootthrough logic, short circuit

protection, shutdown, and UV lockout

BLOCK DIAGRAM

3.5V

REFERENCE

9

VREF

GND

N DRV H

N DRV L

ISENSE

PWR GOOD

19

UVLO

16

12

17

8

VDD

+

–

18

VCC

+

–

5

RANGE

VDAC

1

D0

2

D1

3

D2

4

D3

2 CHORD

4 BIT DAC

4.4V

10.5V

20

PROTECT

3.5V

5V

10

6

SHDN

+

–

+

–

+

–

VFB

VDAC + 3%

VDAC - 3%

+

–

+

–

VFB

VDAC - 3%

VDAC - 10%

VDAC + 3%

VDAC + 10%

VFB

11

PWR GND

15

CONTROL

LOGIC

+

–

–97mV

+

–

VDAC

+

–

COMP

13

200kHz

30µA