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DSQ2102A-QA-00 June 2017 www.richtek.com
RTQ2102A-QA
©
Copyright 2017 Richtek Technology Corporation. All rights reserved. is a registered trademark of Richtek Technology Corporation.
OUT
ON
IN OSC
V
1
T =
Vf
Operation
The RTQ2102A-QA is a low voltage synchronous step-
down converter that can support input voltage ranging from
3V to 6V and the output current can be up to 1.5A. The
RTQ2102A-QA uses ACOT
TM
mode control. To achieve
good stability with low-ESR ceramic capacitors, the ACOT
uses a virtual inductor current ramp generated inside the
IC. This internal ramp signal replaces the ESR ramp
normally provided by the output capacitor's ESR. The ramp
signal and other internal compensations are optimized
for low-ESR ceramic output capacitors.
In steady-state operation, the feedback voltage, with the
virtual inductor current ramp added, is compared to the
reference voltage. When the combined signal is less than
the reference, the on-time one-shot is triggered, as long
as the minimum off-time one-shot is clear and the
measured inductor current (through the synchronous
rectifier) is below the current limit. The on-time one-shot
turns on the high-side switch and the inductor current
ramps up linearly. After the on-time, the high-side switch
is turned off and the synchronous rectifier is turned on
and the inductor current ramps down linearly. At the same
time, the minimum off-time one-shot is triggered to prevent
another immediate on-time during the noisy switching
time and allow the feedback voltage and current sense
signals to settle. The minimum off-time is kept short so
that rapidly-repeated on-times can raise the inductor
current quickly when needed.
PWM Frequency and Adaptive On-Time Control
The on-time can be roughly estimated by the equation :
where f
OSC
is nominal 2.7MHz
Under-Voltage Protection (UVLO)
The UVLO continuously monitors the VCC voltage to make
sure the device works properly. When the VCC is high
enough to reach the UVLO high threshold voltage, the
step-down converter softly starts or pre-bias to its regulated
output voltage. When the VCC decreases to its low
threshold voltage, the device shuts down.
Power Good
When the output voltage is higher than PGOOD rising
threshold, the PGOOD flag is high.
Output Under-Voltage Protection (UVP)
When the output voltage is lower than 66% reference
voltage after soft-start, the UVP is triggered.
Over-Current Protection (OCP)
The RTQ2102A-QA senses the current signal when the
high-side and low-side MOSFET turns on. As a result,
The OCP is a cycle-by-cycle current limit. If an over-current
condition occurs, the converter turns off the next on pulse
until inductor current drops below the OCP limit. If the
OCP is continually activated and the load current is larger
than the current provided by the converter, the output
voltage drops. Also, when the output voltage triggers the
UVP also, the current will drop to ZC and trigger the re-
soft start sequence.
Soft-Start
An internal current source charges an internal capacitor
to build the soft-start ramp voltage. The typical soft-start
time is 150μs.
Over-Temperature Protection (OTP)
The RTQ2102A-QA has an over-temperature protection.
When the device triggers the OTP, the device shuts down
until the temperature is back to normal.
