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RT9232A Datasheet(PDF) 3 Page - Richtek Technology Corporation

Part No. RT9232A
Description  Programmable Frequency Synchronous Buck PWM Controller
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Maker  RICHTEK [Richtek Technology Corporation]
Homepage  http://www.richtek.com
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RT9232A Datasheet(HTML) 3 Page - Richtek Technology Corporation

 
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RT9232A
3
DS9232A-02 March 2007
www.richtek.com
Function Block Diagram
Operation
Startup
RT9232A initializes automatically after receiving both VCC and VIN power. Special power-on sequence is not necessary.
The Power-On Reset (POR) function continually monitors input supply voltages and enable voltage. POR function
monitors IC power via VCC pin and external MOSFET power via SENSE pin. Voltage on SENSE pin is a fixed voltage
drop less than VIN. When voltages on VCC, SENSE, and EN pins exceed their thresholds, POR function initializes soft-
start operation. POR inhibits driver operation while EN pin pulls low. Transitioning EN pin high after input supply voltages
ready initializes soft-start operation.
Soft-Start
After POR function releases soft-start operation, an internal 10uA current source charges an external capacitor on SS
pin (Css) to 5V. Soft-start function clamps both COMP & FB pins to SS pin voltage & a fixed voltage drop less than SS
pin voltage respectively. Thus upper MOSFET turns on at a limited duty and output current overshoot can be reduced.
This method provides a rapid and controlled output voltage rise.
Under Voltage Protection
The under voltage protection function protects the converter from an shorted output by detecting the voltage on FB pin
to monitor the output voltage. The UVP function cycles soft-start function in a hiccup mode. When output voltage lower
than 75% of designated voltage, UVP function initializes soft-start cycles. The soft-start function discharges Css with
10uA current sink and disable PWM operation. Then soft-start function recharges Css and PWM operation resumes.
The soft-start hiccup restarts after SS voltage fully charges to 4V if the output short event still remains. The converter is
shutdown permanently after 3 times hiccup and only restarting supply voltages can enable the converter.
Power-On
Reset (POR)
Soft Start
and
Fault Logic
Oscillator
Driver Logic
EA
PWM
10uA
Reference
SS
GND
FB
SENSE
PHASE
PVCC
LGATE
PGND
UGATE
BOOT
VCC
COMP
RT
POR
V
IN
POR
-
+
+
-
-
+
+
-
0.6V
UV
0.8V
EN
INHIBIT
1.5V
+
+


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