DS8813D Datasheet, PDF (4/23 Pages) Richtek Technology Corporation – Multi-Phase PWM Controller with PWM-VID Reference

RT8813D
Operation
The RT8813D is a 3/2/1 phase synchronous Buck PWM
controller with integrated drivers which are optimized for
high performance graphic microprocessor and computer
applications. The IC integrates a COT (Constant-On-Time)
PWM controller with two MOSFET drivers, as well as
output current monitoring and protection functions.
Referring to the function block diagram of TON Genx, the
synchronous UGATE driver is turned on at the beginning
of each cycle. After the internal one-shot timer expires,
the UGATE driver will be turned off. The pulse width of
this one-shot is determined by the converter's input voltage
and the output voltage to keep the frequency fairly constant
over the input voltage range and output voltage. Another
one-shot sets a minimum off-time.
The RT8813D also features a PWM-VID dynamic voltage
control circuit driven by the pulse width modulation
method. This circuit reduces the device pin count and
enables a wide dynamic voltage range.
Soft-Start (SS)
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 soft-start is finished, the PGOOD open drain
output will be high impedance.
Current Balance
The RT8813D implements internal current balance
mechanism in the current loop. The RT8813D senses per
phase current and compares it with the average current. If
the sensed current of any particular phase is higher than
average current, the on-time of this phase will be adjusted
to be shorter.
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.
Over Voltage Protection (OVP) & Under Voltage
Protection (UVP)
The output voltage is continuously monitored for over
voltage and under voltage protection. When the output
voltage exceeds its set voltage threshold (If V_REFIN ≤ 1.33V,
OV = 2V, or V_REFIN > 1.33V, OV = 1.5 x V_REFIN), UGATE
goes low and LGATE is forced high; when it is less than
40% of its set voltage, under voltage protection is triggered
and then both UGATE and LGATE gate drivers are forced
low. The controller is latched until PVCC is re-supplied
and exceeds the POR rising threshold voltage or EN is
reset.
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DS8813D-00 September 2016