FP5101 datasheet(10/20 Pages) FEELING

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FP5101 / FP5101A

This datasheet contains new product information.

Feeling Technology reserves the rights to modify the product specification without notice.

No liability is assumed as a result of the use of this product. No rights under any patent accompany the sales of the product.

Website: http://www.feeling-tech.com.tw

Rev. 0.64

10/20

Function Description

Power On Reset

The FP5101 / A automatically initializes upon input power VCC. The Power-On Reset (POR)

function continually monitors the bias voltage at the VCC pin. The POR threshold level is typically 9.6V

at VCC rising.

VIN Detection

After POR is outstripped, the FP5101 / A

continuously generates a 10kHz pulse train with 1μs

pulse width to turn on the upper MOSFET for detecting the existence of VIN. FP5101 / A keeps

monitoring SW pin voltage during the detection period. When the SW voltage crosses 1.5V two times,

VIN existence is recognized and the FP5101 / A initiates its soft start cycle as described in next section.

Soft Start

After the existence of VIN is detected, the soft-start (SS) begins automatically. The feedback

voltage (VFB) is clamped by internal linear ramping up SS voltage during this period, causing PWM

pulse width increasing slowly and thus inducing little surge current. The maximum load current is

available after the soft-start cycle is completed. Soft-start completes when SS voltage exceeds internal

reference voltage (0.8V), the time duration is about 3.2ms.

Over Current Protection

The FP5101 / A senses the current flowing through lower MOSFET for over current protection

(OCP) by sensing the SW pin voltage as shown in the Functional Block Diagram.

A 3

0μA current source flows through the internal resistor 21.6kΩ to SW pin causing 0.65V voltage

drop across the resistor. OCP is triggered if the voltage at SW pin (drop of lower MOSFET VDS) is lower

than -0.25V when low side MOSFET conducting. Accordingly inductor current threshold for OCP is a

function of conducting resistance of lower MOSFET RDS (ON) as :

)

(

OCSET





If MOSFET with RDS (ON) = 10mΩ is used, the OCP threshold current is about 25A. Once OCP is

triggered, the FP5101 / A enters hiccup mode and re-soft starts again. The FP5101 / A shuts down

after OCP hiccups twice.

To prevent the over current protection occurs in the normal operating load range, the drift of all

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