DS6550A Datasheet, PDF (3/16 Pages) Richtek Technology Corporation – Synchronous DC-DC Step-Down Controller with 5V LDO

Functional Block Diagram
VO_DIS
FB
EN
Shutdown
Discharge
VREF
113%
VREF
52%
VREF
Soft
Start &
Slew
Rate
Control
Enable
Logic
+ OVP
-
+ UVP
-
+
-
PWM
CMP
10µA
Short during CCM
CS
RT6550A
Power On
Reset
LDO5
Control & Protection Logic
Over-
Temperature
Protection
TON
Generator
PWM
Driver
Logic
LDO5
X(1/8)
Current
-
limit
+
VIN
LDO5
BOOT
UGATE
PHASE
LGATE
GND
Operation
The RT6550A includes constant on-time synchronou step-
down controller and linear regulator.
Buck Controller
In normal operation, the high-side N-MOSFET is turned
on when the output 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
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.
Current Limit
The current limit circuit employs an 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. Thus, the
current to the load exceeds the average output inductor
current, the output voltage falls and eventually crosses
the under-voltage protection threshold, inducing IC
shutdown.
Over-Voltage Protection (OVP) and Under-Voltage
Protection (UVP)
The channel output voltage is continuously monitored for
over-voltage and under-voltage conditions. When the
output voltage exceeds over-voltage threshold (113% of
VOUT), UGATE goes low and LGATE is forced high; when
it is less than 52% of reference voltage, under-voltage
protection is triggered and then both UGATE and LGATE
gate drivers are forced low. The controller is latched until
EN is reset or LDO5 is re-supplied.
LDO5
The LDO5 can be power on by EN. The linear regulator
LDO5 provides 5V regulated output.
Copyright ©2016 Richtek Technology Corporation. All rights reserved.
DS6550A-00 September 2016
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
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