RT6543A/B
Functional Block Diagram
VID0 VID1
To driver Logic
To Power on Reset
Enable
Logic
Reference
Output Gen.
VOUT
OV
2.2V
UV
60% V
REF
PGOOD
V
REF
90% V
REF
+
-
+
-
+
-
Power On Reset
&Central Logic
EN
RGND
VCC
PGOOD
Control & Protection Logic
PVCC
BOOT
UGATE
PH
LGATE
PGND
Soft-Start &
Slew Rate
Control
ISENSEP
ISENSEN
FB
COMP
VSYS
Droop
HIZ
VREF_
DROOP
+
-
EA
TON
Gen.
-
+
PWM
CMP
PWM
Driver
Logic
Zero Current
Detction
Current
Limit
-
+
-
+
V
IN
Detection
FSWSEL
AGND
Frequency
Lock and
Selection
To Power
on Reset
6µA
CS_DIS
X(-1/12)
Operation
The RT6543A/B is a constant on-time synchronous step-
down controller. In normal operation, the high-side N-
MOSFET is turned on when the output voltage is lower
than V
REF
, and is turned off after the internal one-shot
timer expires. While the high-side N-MOSFET is turned
off, the low-side N-MOSFET is turned on to conduct the
inductor current until next cycle begins.
Soft-Start (SS)
For internal soft-start function, an internal current source
charges an internal capacitor to build the soft-start ramp
voltage. The output voltage will track the internal ramp
voltage during soft-start interval.
PGOOD
The power good output is an open-drain architecture. When
the soft-start is finished, the PGOOD open-drain output
will be high impedance.
Copyright
©
2020 Richtek Technology Corporation. All rights reserved.
Current Limit
The current limit circuit employs a unique
“valley”
current
sensing algorithm. If the magnitude of the current sense
signal at PHASE is above the current limit threshold, the
PWM is not allowed to initiate a new cycle. The current
limit threshold can be set with an external voltage setting
resistor on the CS_DIS pin.
Over-Voltage Protection (OVP) & Under-Voltage
Protection (UVP)
The output voltage is continuously monitored for over-
voltage and under-voltage protection. When the output
voltage exceeds 2.2V (Typ.), UGATE goes low and LGATE
is forced high. When the feedback voltage is less than
60% of output voltage, under-voltage protection is triggered
and then both UGATE and LGATE gate drivers are forced
low. The controller is latched until VCC is re-supplied and
exceeds the POR rising threshold voltage or EN is reset.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
4
DS6543A/B-01 March 2020
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
