RT9209 RICHTEK [Richtek Technology Corporation], RT9209 Datasheet - Page 10

• Manufacturer Part Number: RT9209
• Description: Synchronous Buck PWM DC-DC with Enable & PGOOD
• Manufacturer: RICHTEK [Richtek Technology Corporation]

RT9209/A
Application Information
The RT9209/A operates at either single 5V power supply
with a bootstrap UGATE driver or a 5V/12V dual-power
supply form the ATX SMPS. The dual- power supply is
recommended for high current applications, the
RT9209/A can deliver higher gate driving current while
operating with ATX SMPS based on a dual-power supply.
The Bootstrap Operation
In a single power supply system, the UGATE driver of
RT9209/A is powered by an external bootstrap circuit, as
shown in the Figure1. The boot capacitor, C
generates a floating reference. Typically a 0.1μF C
is enough for most of MOSFETs used with the
RT9209/A. The voltage drop between BOOT and A node
is refreshed to a voltage of V
lower MOSFET turning on.
Dual Power Operation
The RT9209/A is designed to supply a regulated 6.5V at
VCC pin automatically when BOOT pin is powered by a
12V. In a system with ATX 5V/12V power supply, the
RT9209/A is ideal for higher current applications due to
the higher gate driving capability, V
= 6.5V. 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.
www.richtek.com
10
1uF
C2
Figure 1. Single 5V power Supply Operation
VCC
RT9209/A
VCC
UGATE
LGATE
BOOT
0.1uF
CC
C1
−
diode drop (V
+
-
UGATE
D1
= 12V and V
A
D
) while the
BOOT
LGATE
BOOT
+
5V
,
VCC
Power On Reset
The Power-On Reset (POR) monitors the supply voltage
(normal +5V) at the VCC pin. The VCC POR level is set
to 4.1V with 0.5V hysteresis. 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 22μA to change a capacitor
slowly. It clamps the ramping of reference voltage at the
input of error amplifier and the pulse-width of the output
driver slowly.
Under Voltage and Over Voltage Protection
The voltage at FB pin is monitored and protected against
OC (over current), and OV (over voltage). The UV
threshold is 0.5V and OV-threshold is 1.0V. Both UV/OV
detection have 30ms triggered delay. When OC or UV
trigged, a hiccup re-start sequence will be initialized, as
shown in Figure 3. Only 3 times of trigger are allowed to
latch off. Hiccup is disabled during soft-start interval.
Shutdown
Pulling low the SS pin by a small single transistor can
shutdown the RT9209/A PWM controller as shown in
typical application circuit.
5V
1uF
C2
Figure 2. Dual Power Supply Operation
Regulator
RT9209/A
6.5V
VCC
BOOT
UGATE
LGATE
DS9209/A-08 March 2007
1uF
C1
A
R1
10
12V
+
5V