FP6329ASOGTR datasheet(10/16 Pages) FITIPOWER

10 / 16 page

FP6329/A/B-1.0-APR-2010

FP6329/A

85T

fitipower integrated technology lnc.

Functional Description

The Power-On Reset (POR) function continually

monitors the input supply voltage and the enable

function.

The POR monitors the bias voltage at the

VCC pin.

When VCC power is ready, the FP6329/A

starts to ramp up the output voltage up to the target

voltage.

Soft-Start

The FP6329/A features soft-start to limit inrush

current and control the output voltage rise at start-up.

The soft-start is accomplished by ramping the

internal reference input from 0V to 0.6V.

The

soft-start interval is 3.5ms typical.

Over-Current Protection

The over-current function protects the converter a

shorted output by using the low side MOSFET

on-resistance RDS-ON to monitor the current.

This

method enhances the converter’s efficiency and

reduces cost by eliminating a current sensing

resistor.

The

over-current

function

cycles

the

soft-start

function in a hiccup mode to provide fault protection.

After four times are counted, the high side and low

side gate will turn off and the output is latched off

until the VCC bias supply is re-started.

A resistor

(ROCSET), connected from the gate of low side

MOSFET to the source of low side MOSFET to set

the over-current trigger level.

An internal 21.5

μA

(typical) current source develops the voltage across

the ROCSET.

The over-current setting equation is

shown as below:

OCSET

µA







21.5

*Note: If ROCSET > 25kΩ, the over-current function will

be disabled.

To avoid the normal operation trigger the OCP

function at load transient and junction temperature.

All parameters variation must be concerned.

(1) The maximum RDS-ON at the highest junction

temperature.

(2) The minimum OCSET current.

Shutdown

Connecting a small transistor to COMP/SD pin, and

pulling the voltage of COMP/SD pin less than 0.4V

can shutdown the FP6329/A.

At this condition, the

FP6329/A is shutdown and high side and low side

MOSFETs are turned off.

Under-Voltage Protection

The under-voltage function monitors the FB voltage

to protection the converter against the output

short-circuit

condition.

The

under-

voltage

threshold is 0.5xVREF.

When UVP happens, the

high side and low side gate will turn off and the

output is latched off until the VCC bias supply is

re-started.

Over-Voltage Protection

The over-voltage function monitors the FB voltage

to protection the converter against the output from

over-voltage.

When the feedback voltage rises to

1.25xVREF, the FP6329/A turns on the low side

MOSFET until the feedback voltage below the OVP

threshold.

During the soft start period, the

over-voltage protection function is disabled.

FP6329ASOGTR Datasheet(PDF) 10 Page - Fitipower Integrated Technology Inc.

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