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參數(shù)資料
| 型號(hào)： | RT9209 |
| 英文描述： | Step-down DC/DC Converter |
| 中文描述： | 降壓直流/直流轉(zhuǎn)換器 |
| 文件頁(yè)數(shù)： | 10/16頁(yè) |
| 文件大?。?/td> | 315K |
| 代理商： | RT9209 |
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RT9203/A
Preliminary
www.richtek.com
10
DS9203/A-04 May 2003
Functional Description
The RT9203/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 RT9203/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
RT9203/A is powered by an external bootstrap circuit,
as shown in the Fig.3. The boot capacitor, C
BOOT
,
generates a floating reference at the PHASE pin.
Typically a 0.1
μ
F C
BOOT
is enough for most of
MOSFETs used with the RT9203/A. The voltage drop
between BOOT and PHASE is refreshed to a voltage
of VCC – diode drop (V
D
) while the lower MOSFET
turning on.
Fig.3 Single 5V power Supply Operation
Dual Power Operation
The RT9203/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 RT9203/A is ideal for higher current
applications due to the higher gate driving capability,
V
UGATE
= 12V and V
LGATE
= 6.0V. A RC (10
/1
μ
F)
filter is also recommended at BOOT pin to prevent the
ringing induced from fast power-on, as shown in Fig.4.
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
0.5V and OV threshold is 1.0V. Both UV and OV
detection are with 30
μ
S delay after triggered. When
OC or UV trigged, a hiccup re-start sequence will be
initialized, as shown in Fig.5 For RT9203, Only 3 times
of trigger are allowed before latching off. But for
RT9203A, UVP will be kept in hiccup mode. Hiccup is
disabled during soft-start interval.
+
BOOT
UGATE
PHASE
LGATE
RT9203/A
VCC
D1
0.1
μ
F
5V
R1
C2
1
μ
F
VCC
+
5V
VCC
LGATE
UGATE
BOOT
R
C2
1uF
RT9203/A
1uF
6.0V
Regulation
10
C
12V
VCC
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