RT9205ACS Ver la hoja de datos (PDF) - Richtek Technology
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RT9205ACS Datasheet PDF : 16 Pages
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RT9205/A
Preliminary
Functional Description
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 Fig.3. The boot capacitor, CBOOT,
generates a floating reference at the PHASE pin.
Typically a 0.1µF CBOOT is enough for most of
MOSFETs used with the RT9205/A. The voltage drop
between BOOT and PHASE is refreshed to a voltage
of VCC – diode drop (VD) while the lower MOSFET
turning on.
R1
C2
VCC BOOT
D1
1µF
UGATE
0.1µF
PHASE
VCC
LGATE
5V
+
RT9205/A
Fig.3 Single 5V power Supply Operation
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, VUGATE = 12V and VLGATE = 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 Fig.4.
VCC
6.0V
Regulation
BOOT
UGATE
R
C 10
1uF
12V
5V
VCC
LGATE
C2
1uF
RT9205/A
Fig.4 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 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 Fig.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.
www.richtek.com
10
DS9205/A-03 May 2003
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