RT9202GS datasheet(9/14 Pages) RICHTEK

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RT9202

DS9202-09

March 2007

www.richtek.com

Application Information

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 Figure 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 (V

D) while

the low side MOSFET turning on.

Dual Power Operation

The RT9202 is 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

(10

Ω/1µF) filter is also recommended at BOOT pin to

prevent the ringing induced from fast power on, as shown

in Figure 2.

VCC

LGATE

PHASE

UGATE

BOOT

VCC

1uF

RT9202

0.1uF

VCC

LGATE

UGATE

BOOT

1uF

RT9202

1uF

6.0V

Regulation

12V

VCC

Figure 1. Single 5V power Supply Operation

Figure 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 Figure 3 the internal 40

µA current

sink (IOCSET) 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 comparator trips to set the over-current latch.

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