RT9202CS datasheet(9/16 Pages) RICHTEK

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RT9202

DS9202-02 August 2002

www.richtek.com

Functional Description

The RT9202 operates at either single 5V power

supply with a bootstrap UGATE driver or 5V/12V

dual-power supply form the ATX SMPS. The dual-

power supply is recommended for high current

application, the RT9202 can deliver higher gate

driving current while operating with ATX SMPS based

on dual-power supply.

The Bootstrap Operation

In a single power supply system, the UGATE driver of

RT9202 is powered by an external bootstrap circuit,

as the Fig.1. The boot capacitor, CBOOT, generates a

floating reference at the PHASE pin. Typically a

0.1

µF CBOOT is enough for most of MOSFETs used

with the RT9202. The voltage drop between BOOT

and PHASE is refreshed to a voltage of VCC – diode

drop (VD) while the low side MOSFET turning on.

Fig.1 Single 5V power Supply Operation

Dual Power Operation

The RT9202 was designed to regulate a 6.0V at VCC

pin automatically when BOOT pin is powered by 12V.

In a system with ATX 5V/12V power supply, the

RT9202 is ideal for higher current application due to

the higher gate driving capability, VUGATE = 7V and

VLGATE = 6.0V. A RC (10Ω/1µF) filter is also

recommended at BOOT pin to prevent the ringing

induced from fast power on, as shown in Fig.2.

Fig.2 Dual Power Supply Operation

Power On Reset

The Power-On Reset (POR) monitors the supply

voltage (normal +5V) at the VCC pin and the input

voltage at the OCSET pin. The VCC POR level is

4.1V with 0.5V hysteresis and the normal level at

OCSET pin is 1.5V (see over-current protection). The

POR function initiates soft-start operation after all

supply voltages exceed their POR thresholds.

Soft Start

A built-in soft-start is used to prevent surge current

from power supply input during power on. The soft-

start voltage is controlled by an internal digital

counter. It clamps the ramping of reference voltage at

the input of error amplifier and the pulse-width of the

output driver slowly. The typical soft-start duration is

2mS.

Over-Current Protection

The over current protection (OCP) function of the

RT9202 is triggered when the voltage across the

RDS(ON) of upper side MOSFET that developed by

drain current exceeds over-current tripping level. An

external resistor (ROCSET) programs the over-current

tripping level of the PWM converter. As shown on

Fig.1, the internal 40

µA current sink (I

OCSET) develops

a voltage across ROCSET (VSET) that is referenced to

VIN. The DRIVE signal enables the over-current

comparator (OC). When the voltage across the upper

MOSFET (VDS(ON)) exceeds VSET, the over-current

BOOT

UGATE

PHASE

LGATE

RT9202

VCC

0.1

µF

VCC

BOOT

UGATE

LGATE

6.0V

Regulator

VCC

µF

12V

VCC

RT9202

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