RT9204CS datasheet(8/14 Pages) RICHTEK

8 / 14 page

RT9204

Preliminary

www.richtek-ic.com.tw

DS9204-00 February 2002

Functional Description

The RT9204 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 RT9204 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

RT9204 is powered by an external bootstrap circuit,

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

floating reference at the PHASE node. Typically a

0.1

µF CBOOT is enough for most of MOSFETs used

with the RT9204. The voltage drop between BOOT

and PHASE node 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 RT9204 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

RT9204 is ideal for higher current application due to

the higher gate driving capability, VUGATE = 7V. A RC

(10

Ω/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.

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.3.

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

is disabled during soft-start interval.

BOOT

UGATE

PHASE

RT9204

0.1

µF

VCC

BOOT

UGATE

6.0V

Regulator

µF

12V

VCC

RT9204

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