rt9202b Richtek Technology Corporation, rt9202b Datasheet - Page 9

• Manufacturer Part Number: rt9202b
• Description: Single Synchronous Buck Dc-dc Controller
• Manufacturer: Richtek Technology Corporation

Application Information
The RT9202B 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 RT9202B
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
RT9202B is powered by an external bootstrap circuit, as
the Figure 1. The boot capacitor, C
floating reference at the PHASE pin. Typically a 0.1 F
C
RT9202B. The voltage drop between BOOT and PHASE
is refreshed to a voltage of VCC
the low side MOSFET turning on.
Dual Power Operation
The RT9202B 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 RT9202B is
ideal for higher current application due to the higher gate
driving capability, V
(10 /1 F) filter is also recommended at BOOT pin to
prevent the ringing induced from fast power on, as shown
in Figure 2.
DS9202B-03 March 2007
BOOT
1uF
C2
Figure 1. Single 5V power Supply Operation
is enough for most of MOSFETs used with the
VCC
RT9202B
VCC
UGATE
PHASE
LGATE
BOOT
UGATE
R1
= 7V and V
0.1uF
D1
diode drop (V
LGATE
BOOT
, generates a
= 6.0V. A RC
D
) while
5V
VCC
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 RT9202B
is triggered when the voltage across the R
side MOSFET that developed by drain current exceeds
over-current tripping level. An external resistor (R
programs the over-current tripping level of the PWM
converter. As shown on Figure 3 the internal 20 A current
sink (I
that is referenced to V
over-current comparator (OC). When the voltage across
the upper MOSFET (V
current comparator trips to set the over-current latch.
5V
1uF
C2
OCSET
Figure 2. Dual Power Supply Operation
Regulation
) develops a voltage across R
6.0V
RT9202B
VCC
IN
DS(ON)
. The DRIVE signal enables the
BOOT
UGATE
LGATE
) exceeds V
C1
1uF
RT9202B
R1
10
www.richtek.com
DS(ON)
SET
OCSET
, the over-
of upper
12V
OCSET
(V
SET
9
)
)
5V