RT7231/32/33/34
Function Block Diagram
VCC*
VREG5
BOOT
POR &
Reg
VBIAS
OC
UV & OV
SW
V
REG5
2µA
SS
V
IN
FB
VS*
On-Time
FB
+
-
-
Comparator
EN
Min.
Off-Time
V
REF
Control
VREG5
VIN
Driver
SW
PGND
ZC
GND*
Ripple
Gen.
Comparator
-
+
PGOOD*
FB
0.9 x V
REF
* : VCC pin for TSSOP-14 (Exposed Pad) only.
GND pin for TSSOP-14 (Exposed Pad) only.
VS pin for TSSOP-14 (Exposed Pad) only.
PGOOD pin for TSSOP-14 (Exposed Pad) and WDFN-10L 3x3 only.
Operation
The RT7231/32/33/34 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.
Power Good
(for TSSOP-14 (Exposed Pad) and WDFN-10L 3x3 only)
After soft-start is finished, the power good function will be
activated. When the FB is activated, the PGOOD will
become an open-drain output. If the FB is below, the
PGOOD pin will be pulled low.
Internal Regulator
The regulator provides 5V power to supply the internal
control circuit. Connecting a 1μF ceramic capacitor for
decoupling and stability is required.
Soft-Start
In order to prevent the converter output voltage from
overshooting during the startup period, the soft-start
function is necessary. The soft-start time is adjustable
and can be set by an external capacitor.
Current Protection
The inductor current is monitored via the internal switches
in cycle-by-cycle. Once the output voltage drops under
UV threshold, the device will enter latch mode for TSSOP-
14 (Exposed Pad), and hiccup mode for WDFN-10L 3x3.
UVLO Protection
To protect the chip from operating at insufficient supply
voltage, the UVLO is needed. When the input voltage of
VCC is lower than the UVLO falling threshold voltage, the
device will be latch-off.
Output Discharge Control
(for TSSOP-14 (Exposed Pad) only)
When EN pin is low, the RT7231/32 will discharge the
output with an internal 50Ω MOSFET connected between
V
OUT
to GND pin.
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
automatically resume switching
Copyright
©
2013 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
4
DS7231/32/33/34-00
March 2013
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
