RT6541A
Functional Block Diagram
TRIG
PHASE
On-time compute
One shot
S
Q
DRV
UGATE
PHASE
FB
-
+
Q
R
BOOT
Comp
Min Toff
TRIG
One shot
VCC
DRV
Latch
+
1.2V
-
ZCD
Latch
-
0.3V
+
UV
S1
Q
+
-
OV
S1
Q
LGATE
GND
PGOOD
-
0.675V
+
LPM
G0
G1
MODE
RGND
EN
+
-
Voltage
Programmer
SS Timer
Thermal
Shutdown
DEM
OC threshold
1/10
10µA
CS
Operation
The RT6541A 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 VREF, 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
©
2019 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 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 1.2V (typ.), UGATE goes low and LGATE
is forced high. When the feedback voltage is less than
0.3V (typ.), 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.
DS6541A-02
September 2019
www.richtek.com
3
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
