Shenzhen H&M Semiconductor Co.Ltd

http: //www.hmsemi.com

4

HM6291

Function Description

Operation

The HM6291 is a current mode boost converter. The constant switching frequency is

1MHz and operates with pulse width modulation (PWM). Build-in 18V / 2A MOSFET

provides a high output voltage. The control loop architecture is peak current mode control;

therefore slope compensation circuit is added to the current signal to allow stable

operation for duty cycles larger than 50%.

Soft Start Function

Soft start circuitry is integrated into HM6291 to avoid inrush current during power on.

After the IC is enabled, the output of error amplifier is clamped by the internal soft-start

function, which causes PWM pulse width increasing slowly and thus reducing input surge

current.

Current Limit Program

A resistor between OC and GND pin programs peak switch current. The resistor value

should be between 10k and 100k. The current limit will be set from 2.5A to 0.5A. Keep

traces at this pin as short as possible. Do not put capacitance at this pin. To set the over

current trip point according to the following equation:

51000

I

OCP

R

S

Over Temperature Protection (OTP)

HM6291 will turn off the power MOSFET automatically when the internal junction

temperature is over 150°C. The power MOSFET wake up when the junction temperature

drops 30°C under the OTP threshold temperature.

Output Disconnect

When power on and the EN pin will be pulled high. The HM6291 start up and operates.

The external PMOS is turned on and current through it for output loading. While output

loading is increase, output voltage is drop. When the FB pin voltage is under 0.3V, the EN

pin sinks 20μA current, the external PMOS will be turn off. The output short condition will

be disconnected.