RT9202
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
LGATE
5V
6.0V
Regulation
BOOT
C1
1uF
UGATE
R1
10
12V
5V
+
VCC
VCC
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, C
BOOT
, generates a
floating reference at the PHASE pin. Typically a 0.1µF
C
BOOT
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.
R1
VCC
C2
1uF
D1
5V
0.1uF
+
C2
1uF
RT9202
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
BOOT
UGATE
PHASE
VCC
LGATE
RT9202
Figure 1. Single 5V power Supply Operation
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, V
UGATE
= 7V and V
LGATE
= 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 Figure 2.
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 R
DS(ON)
of upper
side MOSFET that developed by drain current exceeds
over-current tripping level. An external resistor (R
OCSET
)
programs the over-current tripping level of the PWM
converter. As shown on Figure 3 the internal 40µA current
sink (I
OCSET
) develops a voltage across R
OCSET
(V
SET
)
that is referenced to V
IN
. The DRIVE signal enables the
over-current comparator (OC). When the voltage across
the upper MOSFET (V
DS(ON)
) exceeds V
SET
, the over-
current comparator trips to set the over-current latch.
www.richtek.com
9
DS9202-09 March 2007
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
