RT6232A/B
Operation
The RT6232A/B is a synchronous step-down converter
with advanced constant on-time control mode. Using
the ACOT
TM
control mode can reduce the output
capacitance and provide fast transient response. It can
minimize the component size without additional external
compensation network.
Current Protection
The inductor current is monitored via the internal
switches cycle-by-cycle. Once the output voltage drops
under UV threshold, the RT6232A/B will enter hiccup
mode.
Soft-Start
The RT6232A/B provides adjustable soft-start function.
When the EN pin becomes high, the SS charge current
(I
SS
) begins charging the capacitor which is connected
from the SS pin to GND (C
SS
).The soft-start function is
used to prevent large inrush current while converter is
being powered-up. The soft-start timing can be
programmed by the external capacitor C
SS
between SS
and GND. An internal current source I
SS
(1A) charges
an external capacitor to build a soft-start ramp voltage.
The V
FB
voltage will track the soft-start ramp voltage
during soft-start interval. The typical soft-start time is
calculated as follows :
Soft-Start time t
SS
= T1 + T2 = 50s + C
SS
x 0.9 / I
SS
Time from EN high to PG signal ready = 50s + C
SS
x
0.9 / I
SS
+ C
SS
x 0.65 / I
SS
EN
LX
t
Output Under-Voltage Protection and Hiccup Mode
The RT6232A/B includes output under-voltage
protection (UVP) against over-load or short-circuited
condition by constantly monitoring the feedback voltage
V
FB
. If V
FB
drops below the under-voltage protection trip
threshold (typically 50% of the internal feedback
reference voltage), the UV comparator will go high to
turn off both the internal high-side and low-side
MOSFET switches. If the output under-voltage condition
continues for a period of time, the RT6232A/B will enter
output under-voltage protection with hiccup mode.
During hiccup mode, the IC will shut down for
t
HICCUP_OFF
(C
SS
x 3.6/I
SS
), and then attempt to
recover automatically for t
HICCUP_ON
(C
SS
x 1.3/I
SS
).
Upon completion of the soft-start sequence, if the fault
condition is removed, the converter will resume normal
operation; otherwise, such cycle for auto-recovery will
be repeated until the fault condition is cleared. Hiccup
mode allows the circuit to operate safely with low input
current and power dissipation, and then resume normal
operation as soon as the over-load or short-circuit
condition is removed.
Abnormal case
detected (UV)
VOUT
t
HICCUP_ON
= C
SS
x 1.3/I
SS
t
HICCUP_OFF
= C
SS
x 3.6/I
SS
t
UVLO Protection
SS = 1.55V
SS
To protect the chip from operating at insufficient supply
voltage, the UVLO is needed. When the input voltage of
VIN is lower than the UVLO falling threshold voltage, the
FB
device will be lockout.
Thermal Shutdown
When the junction temperature exceeds the OTP
threshold value, the IC will shut down the switching
operation. Once the junction temperature cools down
and is lower than the OTP lower threshold, the
converter will autocratically resume switching.
is a registered trademark of Richtek Technology Corporation
T1
T2
PG
T1 : EN delay, from EN go high to SS start rising, T1 = 50μs;
T2 : normal SS, from FB rising to settled, T2 = C
SS
x 0.9/I
SS
;
PG go high after SSOK (SS = 1.55V)
Copyright © 2018 Richtek Technology Corporation. All rights reserved.
DS6232A/B-02
December
2018
www.richtek.com
3
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
