FP6326 Просмотр технического описания (PDF) - Unspecified

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FP6326

Synchronous Buck PWM DC-DC Controller

Unspecified 

fitipower integrated technology lnc.

FP6326/A

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

When VCC power is ready, the FP6326/A starts to

ramp up the output voltage up to the target voltage.

Soft-Start

The FP6326/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 0.8V. 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 FP6326/A. At this condition, the

FP6326/A 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 0.75xVREF. The UV has 20us

triggered delay. When UVP happens, the

converter re-starts up without latching off.

Over-Voltage Protection

The over-voltage function monitors the FB voltage

to protection the converter against the output from

over-voltage. When the output voltage rises to

1.2xVREF, the FP6326/A turns on the low side

MOSFET until the output voltage below the OVP

threshold.

FP6326/A-1.1-JUL-2009

10

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