MP6922—DUAL FAST TURN-OFF INTELLIGENT CONTROLLER
Latch off during Burst Operation
Light-load Latch-off Function
The gate driver of MP6922 is latched to save the
driver loss at light-load condition to improve light
load efficiency.
The IC also monitors the synchronous MOSFET
off period, if the off period is longer than the light-
load-enter off period width (TLL-OFF), MP6922
enters light-load mode and latches off the gate
driver.
Latch off during Normal Operation
When the MOSFET conducting period during
each switching cycle keeps lower than 2.2us (TLL),
the MP6922 falls into light-load mode and latches
off the MOSFET after 120us delay (light-load-
The gate driver is unlatched when the drain-
source voltage of the synchronous MOSFET VDS
drops below -70mV.
enter delay, TLL-Delay
)
Reverse Current Protection Function
After falling into light-load mode, MP6922
monitors the MOSFET’s body diode conducting
period by sensing VDS (when VDS exceeds -
250mV (VLL-DS), MP6922 considers the
MOSFET’s body diode conducting period
finishes). If the MOSFET’s body diode
conducting period is longer than ~2.4us (TLL+TLL-
H), the light-load mode is finished and the
MOSFET is unlatched to restart the synchronous
rectification.
When the LLC system operates in CCM with very
high frequency, the synchronous current may get
reverse before the IC turns off the gate driver
which leads to shoot through (in center-tapped
output with full-wave rectification topology).
MP6922 has protection function to latch off the
gate driver when the current reverses before the
driver signal is pulled low.
When the synchronous current reverses, the high
spike can be observed between Drain-Source of
MOSFET. The MP6922 monitors the voltage by
RCP pin through a voltage divider. When the
voltage of RCP pin exceeds VRCP, MP6922 will
latch the driver signal of both channels for
~100us (TRCP) to protect the synchronous
MOSFET. At the end of TRCP, MP6922 restarts
the synchronous rectification.
For SOIC14 package MP6922 with LL pin, the
TLL could be adjusted by an external resistor:
RLL
T = 2.2μs⋅
LL
100kΩ
MP6922 Rev. 1.23
9/19/2012
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