rt9232a Richtek Technology Corporation, rt9232a Datasheet - Page 3

• Manufacturer Part Number: rt9232a
• Description: Programmable Frequency Synchronous Buck Controller
• Manufacturer: Richtek Technology Corporation

Function Block Diagram
Operation
Startup
RT9232A initializes automatically after receiving both V
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 V
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
shutdown permanently after 3 times hiccup and only restarting supply voltages can enable the converter.
DS9232A-02 March 2007
COMP
IN
. When voltages on VCC, SENSE, and EN pins exceed their thresholds, POR function initializes soft-
SS
FB
Reference
10uA
0.8V
0.6V
+
-
+
EA
+
-
Oscillator
UV
RT
+
+
-
CC
PWM
and V
Reset (POR)
POR
Fault Logic
VCC
to 4V if the output
Power-On
Soft Start
and
IN
power. Special power-on sequence is not necessary.
EN
INHIBIT
Driver Logic
POR
V
IN
short event still remains. The converter is
+
-
1.5V
SENSE
BOOT
UGATE
PHASE
PVCC
LGATE
PGND
GND
RT9232A
www.richtek.com
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