LD7120

2/21/2005

1

Leadtrend Technology Corporation

LD7120-DS-05 February 2005

Single Synchronous Buck PWM Controller

General Description

The LD7120 is a single PWM controller designed to drive

N-channel MOSFET in a synchronous buck topology. The IC

integrates the controller, output adjustment, monitoring, and

protection functions in a single 8-pin package.

The LD7120 provides simple, single feedback loop, voltage

mode controller with fast transient response. Internal 0.8V

temperature-compensated reference voltage is designed to

meet low output voltage for further applications. A fixed

300KHz frequency oscillator reduces design complexity,

while balancing typical application cost and efficiency.

The LD7120 features over current protection. The output

current is monitored by sensing the voltage drop across the

MOSFET RDS(ON), which eliminates the need for a current

sensing resistor.

Features

•

Operates from 5V

•

Drives Two N-channel MOSFETs

•

Fixed 300KHz Constant Switching Frequency

•

Full 0~100% Duty-cycle

•

Programmable Over Current Protection

•

Internal Soft-start

•

Fast Transient Response

•

Under-voltage Lockout

Applications

•

Motherboard

•

Graphic Cards

•

5V Input DC/DC Converter

•

Memory Supplies

•

Cable Modem, Set Top Box and DSL Modems

•

DSP and Core Communications Processor Supplies

Typical Application

FB

OCSET

LGATE

PHASE

UGATE

BOOT

VCC

GND

Vin= 5V

Vout

R3

6.19K

LD7120

C9

470pF

C12

0.1uF

C7

1uF

C5

330uF

C6

330uF

D1

CH551H-30

C1

0.1uF

R2

10K

C10

8.2nF

R1

1K

R4

2.15K

R5

62 ohm

Q1

Q2

C11

18nF

C13

NC

R7

0 ohm

R6

NC

L1 2uH

C2

470uF

C3

470uF

C4

0.1uF

C8

1uF

7

6

1

2

8

4

3

5