RT9202CS datasheet(10/16 Pages) RICHTEK

10 / 16 page

RT9202

www.richtek.com

DS9202-02 August 2002

comparator trips to set the over-current latch. Both

VSET and VDS are referenced to VIN and a small

capacitor across ROCSET helps VOCSET tracking the

variations of VIN due to MOSFET switching. The over-

current function will be tripped at a peak inductor

current (IPEAK) determined by:

The OC trip point varies with MOSFET’s RDS(ON)

temperature variations. The temperature coefficient

of IOCSET is 2500ppm that is used to compensate

RDS(ON) temperature variations. To avoid over-current

tripping

the

normal

operating

load

range,

determine the ROCSET resistor value from the equation

above with:

1. The maximum RSD(ON) at the highest junction

temperature

2. The minimum IOCSET from the characteristics

3. Determine IPEAK for IPEAK

> I

OUT(MAX) + (

∆I)/2

where

∆I is the output inductor ripple current.

Fig.3

Under Voltage and Over Voltage Protection

The voltage at FB pin is monitored and protected

against OC (over current), UV (under voltage), and

OV (over voltage). The UV threshold is 0.5V and OV-

threshold is 1.0V. Both UV/OV detection have 30

µS

triggered delay. When OC or UV trigged, a hiccup re-

start sequence will be initialized, as shown in Fig.4.

Only 3 times of trigger are allowed to latch off. Hiccup

is disabled during soft-start interval.

Fig. 4

Shutdown

Pulling low the OCSET pin by a small single

transistor can shutdown the RT9202 PWM controller

as shown in typical application circuit.

GATE

CONTROL

PWM

DRIVE

VCC

UGATE

PHASE

ROCSET

OCSET

IOCSET

µA

VPHASE = VIN - VDS

VOCSET = VIN - VSET

VSET+

OVER-CURRENT TRIP:

VDS > VSET

iD ×R DS(ON) > IOCSET × ROCSET

VIN = +5V

VDS+

T0T1

TIME

COUNT = 1 COUNT = 2

COUNT = 3

OVERLOAD

APPLIED

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