RT6308A
Functional Block Diagram
VIN
BOOT
Input UVLO
4.2V
LX
ILMT
EN
-
+
PWM
Control
&
Protect
Logic
Current Sense
Internal
SST
R
DIS
Thermal
PGND
Protection
PGOOD
AGND
+
0.6V
FB
-
EN
5V
LDO
VIN
VCC
4.7V
+
-
BYP
Operation
Over-Current Limit
Overall
The RT6308Ais an advanced constant on-time (ACOTTM)
mode synchronous buck converter. The main control loop
of the RT6308A uses an ACOTTM mode control which
provides a very fast transient response.
The RT6308A current limit is adjustable (8A, 10A, 12A)
by ILMT pin and it is a cycle-by-cycle “valley” type,
measuring the inductor current through the synchronous
rectifier during the off-time while the inductor current ramps
down. If output voltage drops below the output under-voltage
protection level, the RT6308A will stop switching to avoid
excessive heat.
Internal VCC Regulator
The RT6308A includes a 5V linear regulator (VCC). The
VCC regulator steps down input voltage to supply both
internal circuitry and gate drivers.Do not connect the VCC
pin to external loads.
Output Over-Voltage Protection (OVP) and Under-
Voltage Protection (UVP)
The RT6308A includes output Over-Voltage Protection
(OVP) and output under-voltage protection (UVP). If the
output voltage rises above OVP threshold or drops below
UVP threshold for longer than 20μs (typical), the OVP or
UVP function is triggered.
VCC Bypass Function
When PGOODis pulled high and BYP pin of the RT6308A
voltage is above 4.7V, an internal 3Ω P-MOSFET switch
connects VCC to the BYP pin while the VCC linear
regulator is simultaneously turned off.
Power Good
Soft-Start
The power good output is an open drain output that requires
a pull-up resistor. PGOOD will be pulled high after soft-
start is over and the output reaches 90% of its set voltage.
There is a 10μs delay built into PGOOD circuitry to prevent
false transition.
The RT6308A provides an internal soft-start function to
prevent large inrush current and output voltage overshoot.
The typical soft-start duration is around 0.6ms.
Copyright 2019 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
DS6308A-00 October 2019
www.richtek.com
3
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
