RT2856H
Function Block Diagram
PGOOD EN
VIN
PVIN
UV
Comparator
Thermal
Detector
I
hys
I
P
UVLO
91% V
REF
PGOOD
Logic
Regulator
Shutdown
109% V
REF
Logic
V
= 1.21V
OV
EN
Comparator
BOOT
LX
Shutdown
Slope
Compensation
High-Side
Current Sense
I
SS
Power Stage
Control
Logic,
Driver, and
Boot UVLO
SS/TR
FB
+
V
REF
+
Current
Comparator
-
Voltage
Reference
Oscillator with
RT/SYNC
Function
Low-Side
Current Sense
GND
COMP
RT/SYNC
Operation
UV Comparator
Error Amplifier
If the feedback voltage (VFB) is lower than threshold voltage
(91% of VREF), the UV Comparator's output goes high
and the logic control circuit is allowed to turn on the
MOSFET to pull PGOOD pin to low.
The device uses a transconductance error amplifier. The
error amplifier compares the FB pin voltage with the SS/
TR pin voltage and the internal reference voltage which is
0.8V. The transconductance of the error amplifier is
1300μA/V during normal operation. The compensation
network should be connected between the COMP pin and
ground.
OV Comparator
If the feedback voltage (VFB) is higher than threshold voltage
(109% of VREF), the OV Comparator's output goes high
and the logic control circuit is allowed to turn on the
MOSFET to pull PGOOD pin to low.
Oscillator with RT/SYNC function
The switching frequency is adjustable by an external
resistor connected between the RT/SYNC pin and GND.
The available frequency range is from 200kHz to 1.6MHz.
An internal synchronized circuit has been implemented
to switch from RT mode to SYNC mode. To implement
the synchronization function, connect a square wave clock
signal to the RT/SYNC pin with a duty cycle between
10% to 90%. The switching cycle is synchronized to the
falling edge of the external clock at RT/SYNC pin.
Voltage Reference
The converter produces a precise 1% voltage reference
over-temperature by scaling the output of a temperature
stable bandgap circuit.
Copyright 2019 Richtek Technology Corporation. All rights reserved.
©
is a registered trademark of Richtek Technology Corporation.
DS2856H-07 June 2019
www.richtek.com
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