FP6321 Ver la hoja de datos (PDF) - Unspecified

Número de pieza

componentes Descripción

Lista de partido

FP6321

Synchronous Buck PWM DC-DC Controller

Unspecified 

fitipower integrated technology lnc.

FP6321

Functional Description

Initialization

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 and the input voltage (VIN) on the phase

pin. After VCC power is ready, turning on the high

side MOS by pulse cycle. After high side MOS

turns on, the phase pin voltage is very close to VIN.

The VIN power is ready by sensing the phase pin

voltage reaches 1.5V four times.

Soft-Start

The FP6321 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 0.8V. 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 MOSFET will turn off and the

output is latched off.

A resistor (ROCSET), connected from OCSET pin to

the source of high side MOSFET and the drain of

low side MOSFET to set the over-current triple

level. An internal 40uA (typical) current source

develops the voltage across the ROCSET. The

over-current setting equation is shown as below:

IOCSET

=

40uA × ROCSET

RDS−ON

− 0.4V

Shutdown

Connecting a small transistor to OCSET pin and

pulling the OCSET voltage less than 0.15V can

shutdown the FP6321. At this condition, the

FP6321 is shutdown and high side and low side

MOSFETS are turned off. The output is floating.

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 75% VREF. The UV has 20us triggered delay. The

FP6321 will always trigger Vin power sensing after

4 times UV. The under- voltage protection is disable

during the soft-start interval.

FP6321-1.3 -FEB-2010

9

Share Link: