rt9232b Richtek Technology Corporation, rt9232b Datasheet - Page 3

• Manufacturer Part Number: rt9232b
• Description: Programmable Frequency Synchronous Buck Controller
• Manufacturer: Richtek Technology Corporation

Function Block Diagram
Operation
Startup
RT9232B initializes automatically after receiving both V
and V
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 OCSET pin. Voltage on
OCSET pin is a fixed voltage drop less than V
voltages on VCC, OCSET, and EN pins exceed their
thresholds, POR function initializes
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.
DS9232B-03 March 2007
IN
power. Special power-on sequence is not
COMP
SS
FB
Reference
10uA
0.8V
0.6V
soft-start operation.
+
+
-
EA
+
-
Oscillator
IN
UV
RT
. When
+
+
-
CC
PWM
Reset (POR)
VCC
POR
Fault Logic
Power-On
Soft Start
and
OCP
The OCP function monitors output current by using upper
MOSFET R
function in a hiccup mode. Overcurrent triggering level
can be arbitrarily set by adjusting R
current sink makes a voltage drop across R
V
initializes soft-start cycles. The soft-start function
discharges C
function. 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. The OCP funcion will be triggered
as inductor current reach :
IN
I
L(MAX)
EN
. When V
INHIBIT
Driver Logic
=
I
OCSET
DS(ON)
PHASE
SS
-
+
with 10μA current sink and disable PWM
R
DS(ON)
. The OCP function cycles soft-start
×
is lower than V
R
OCSET
200uA
OCSET
OCSET
RT9232B
OCSET
BOOT
UGATE
PHASE
PVCC
LGATE
PGND
GND
. An Internal 200μA
www.richtek.com
, OCP function
OCSET
from
3