MP3908

Current Mode PWM Controller

with Synchronous Secondary Gate Drive

MP3908 Rev.0.9

www.MonolithicPower.com

1

8/29/2008

MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited.

© 2008 MPS. All Rights Reserved.

The Future of Analog IC Technology

DESCRIPTION

The MP3908 is a flexible current-mode PWM

controller

optimized

for

power-supply

applications.

The MP3908 features resistor-

programmable dead-time control to optimize

efficiency for a broad number of different

configurations, and a synchronous secondary

gate drive. The MOSFET drivers are capable

of driving >10A MOSFETs. It has an operational

current of typically 270µA and can accommodate

off-line, Telecom and non-isolated applications.

Under-voltage

lockout,

soft-start,

slope

compensation and peak current limiting are all

included. In a boost application, with an output

voltage of less than 28V, the current sense pin

can connect directly to the drain of the external

switch. This eliminates the requirement for an

additional current sensing element and its

associated efficiency loss.

While designed for boost applications, the MP3908

can also be used for other topologies including

Forward, Flyback and Sepic. The 10V gate driver

compliance minimizes the power loss of the external

MOSFET while allowing the use of a wide variety of

standard

threshold

devices.

An

externally

programmable delay following the turn off of the

synchronous rectifier allows the incorporation of

secondary side synchronous rectifier

The MP3908 is available in space saving 10-pin

MSOP package.

FEATURES

• Programmable Dead-Time

• Synchronous Secondary Gate Drive

• Current Mode Control

• 10V MOSFET Gate Drivers

• Drives >10A MOSFETs

• Soft-Start

• Cycle-by-Cycle Current Limiting

• Slope Current Compensation

• 50µA Shutdown Current

• 270uA typical Operating Current

• 250KHz Constant Frequency Operation

• Applicable to Boost, SEPIC, Flyback and

Forward Topologies

• Available in a 10-Pin MSOP Package

APPLICATIONS

• PoE PD Power Supplies

• TV CCFL Power Generation

• Telecom Isolated Power

• Brick Modules

• Off-line Controller

“MPS” and “The Future of Analog IC Technology” are Registered Trademarks of

Monolithic Power Systems, Inc.

TYPICAL APPLICATION

MP3908

VCC

CSS

GND

EN

9

6

10

4

3

1

7

8

5

2

ISENSE

SYNC

MAIN

COMP

DELAY

ADJ

FB

T1

60

65

70

75

80

85

90

95

0123456

OUTPUT CURRENT (A)

Efficiency vs.

Output Current