RT6575A/B
Functional Block Diagram
BOOT1
UGATE1
PHASE1
LDO5
Channel 1
Buck
Controller
Channel 2
Buck
Controller
LDO5
BOOT2
UGATE2
PHASE2
LGATE1
FB1
CS1
BYP1
VCLK
LGATE2
FB2
CS2
PGOOD
OSC
GND
SW5 Threshold
BYP1
Power-On
Sequence
Clear Fault Latch
EN1
EN2
LDO5
LDO5
VIN
REF
LDO3
BYP1
LDO3
Operation
The RT6575A/B includes two constant on-time
synchronous step-down controllers and two linear
regulators.
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.
PGOOD
The power good output is an open-drain architecture. When
the two channels soft-start are both finished, the PGOOD
open-drain output will be high impedance.
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. 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.
Copyright
©
2016 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
4
DS6575A/B-03 February 2016
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
