MP2467 Datasheet, PDF (9/17 Pages) Monolithic Power Systems – 2.5A, 36V, 500kHz Step-Down Converter

MP2467 – 2.5A, 36V, 500KHz STEP-DOWN CONVERTER
Current Comparator and Current Limit
The power MOSFET current is accurately
sensed via a current sense MOSFET. It is then
fed to the high speed current comparator for the
current mode control purpose. The current
comparator takes this sensed current as one of
its inputs. When the power MOSFET is turned
on, the comparator is first blanked till the end of
the turn-on transition to avoid noise issues. The
comparator then compares the power switch
current with the COMP voltage. When the
sensed current is higher than the COMP
voltage, the comparator output is low, turning
off the power MOSFET. The cycle-by-cycle
maximum current of the internal power
MOSFET is internally limited.
Startup and Shutdown
If both VIN and EN are higher than their
appropriate thresholds, the chip starts. The
reference block starts first, generating stable
reference voltage and currents, and then the
internal regulator is enabled. The regulator
provides stable supply for the remaining
circuitries.
While the internal supply rail is up, an internal
timer holds the signaling path of the power
MOSFET turn-on at OFF for about 50µs to
blank the startup glitches. When the internal
soft-start block is enabled, it first holds its SS
output low to ensure the reamining circuitries
are ready and then slowly ramps up.
Three events can shut down the chip: EN low,
VIN low and thermal shutdown. In the shutdown
procedure, the signaling path is first blocked to
avoid any fault triggering. The COMP voltage
and the internal supply rail are then pulled down.
The floating driver is not subject to this
shutdown command.
MP2467 Rev. 1.1
www.MonolithicPower.com
9
1/25/2010
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