RT9202CS ETC, RT9202CS Datasheet - Page 9

• Manufacturer Part Number: RT9202CS
• Description: SINGLE SYNCHRONOUS BUCK PWM DC-DC CONTROLLER
• Manufacturer: ETC

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, C
floating reference at the PHASE pin. Typically a
0.1µF C
with the RT9202. The voltage drop between BOOT
and PHASE is refreshed to a voltage of VCC – diode
drop (V
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, V
V
recommended at BOOT pin to prevent the ringing
induced from fast power on, as shown in Fig.2.
DS9202-02 August 2002
LGATE
C2
1µF
Fig.1 Single 5V power Supply Operation
D
BOOT
) while the low side MOSFET turning on.
= 6.0V. A RC (10Ω/1µF) filter is also
RT9202
VCC
VCC
is enough for most of MOSFETs used
UGATE
PHASE
LGATE
BOOT
R1
0.1µF
D1
BOOT
UGATE
, generates a
= 7V and
+
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
RT9202 is triggered when the voltage across the
R
drain current exceeds over-current tripping level. An
external resistor (R
tripping level of the PWM converter. As shown on
Fig.1, the internal 40µA current sink (I
a voltage across R
V
comparator (OC). When the voltage across the upper
MOSFET (V
IN
DS(ON)
C2
1µF
. The DRIVE signal enables the over-current
of upper side MOSFET that developed by
Fig.2 Dual Power Supply Operation
Regulator
DS(ON)
6.0V
RT9202
) exceeds V
OCSET
OCSET
VCC
) programs the over-current
(V
BOOT
LGATE
UGATE
SET
) that is referenced to
SET
C1
1µF
, the over-current
RT9202
OCSET
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R1
10
) develops
12V
+
5V
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