RT6576F
Operation
The RT6576F 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 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) & Under-Voltage
Protection (UVP)
The two channel output voltages are 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 ENx is reset or LDO5 is re-supplied.
LDO5 and LDO3
When the VIN voltage exceeds the POR rising threshold,
LDO3 and LDO5 will default turn-on. The linear regulator
LDO5 and LDO3 provide 5V and 3.3V regulated output.
Switching Over
The BYP1 is connected to the Channel 1 output. After the
Channel 1 output voltage exceeds the set threshold
(4.66V), the output will be bypassed to the LDO5 output
to maximize the efficiency.
Copyright
©
2018 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
www.richtek.com
4
DS6576F-00 August 2018
RICHTEK [ RICHTEK TECHNOLOGY CORPORATION ]
