rt9205 Richtek Technology Corporation, rt9205 Datasheet - Page 10

• Manufacturer Part Number: rt9205
• Description: Dual Regulators - Synchronous Buck Pwm Dc-dc And Linear Controller
• Manufacturer: Richtek Technology Corporation

RT9205/A
Application Information
The RT9205/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 RT9205/
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
RT9205/A is powered by an external bootstrap circuit, as
shown in the Figure 3. The boot capacitor, C
generates a floating reference at the PHASE pin. Typically
a 0.1μF C
with the RT9205/A. The voltage drop between BOOT and
PHASE is refreshed to a voltage of VCC
(V
Dual Power Operation
The RT9205/A was designed to supply a regulated 6.0V
at VCC pin automatically when BOOT pin is powered by
a 12V. In a system with ATX 5V/12V power supply, the
RT9205/A is ideal for higher current applications due to
the higher gate driving capability, V
V
at BOOT pin to prevent the ringing induced from fast
power-on, as shown in Figure 4.
www.richtek.com
10
1uF
C2
LGATE
D
) while the lower MOSFET turning on.
Figure 3. Single 5V power Supply Operation
= 6.0V. A RC (10Ω/1μF) filter is also recommended
VCC
RT9205/A
BOOT
VCC
is enough for most of MOSFETs used
UGATE
PHASE
LGATE
BOOT
R1
0.1uF
D1
UGATE
−
= 12V and
diode drop
BOOT
,
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 set to 4.1V with 0.5V
hysteresis and the normal level at OCSET pin is set to
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 powering on. The soft-start
voltage is controlled by an internal digital counter. It slows
down and clamps the ramping of reference voltage at the
input of error amplifier and the pulse-width of the output
driver. The typical soft-start duration is 2.5ms.
Under Voltage and Over Voltage Protection
The voltage presents at FB pin is monitored and protected
against OC (over current), UV (under voltage), and OV
(over voltage). The UV threshold is 0.56V and
OV-threshold is 1.0V. Both UV and OV detection are with
30μs delay after triggered. When OC or UV trigged, a
hiccup re-start sequence will be initialized, as shown in
Figure 5. For RT9205, only 3 times of trigger are allowed
before latching off. But for RT9205A, UVP will be kept in
hiccup mode. Hiccup is disabled during soft-start interval.
1uF
C2
Figure 4. Dual Power Supply Operation
Regulation
RT9205/A
6.0V
VCC
BOOT
UGATE
LGATE
DS9205/A-09 October 2008
1uF
C
10
R
12V
5V