MP1495 – SYNCHRONOUS STEP-DOWN CONVERTER
This protection mode is especially useful when
the output is dead-shorted to ground. The
average short-circuit current is greatly reduced
to alleviate the thermal issue and to protect the
regulator. The MP1495 exits the hiccup mode
once the over-current condition is removed.
Thermal Shutdown
Thermal shutdown prevents the chip from
operating at exceedingly high temperatures.
When the silicon die temperature exceeds
150°C, it shuts down the whole chip. When the
temperature drops below its lower threshold
(typically 130°C) the chip is enabled again.
Floating Driver and Bootstrap Charging
An external bootstrap capacitor powers the
floating power MOSFET driver. This floating
driver has its own UVLO protection, with a
rising threshold of 2.2V and hysteresis of
150mV. The bootstrap capacitor voltage is
regulated internally by VIN through D1, M1, C4,
L1 and C2 (Figure 3). If (VIN-VSW) exceeds 5V,
U1 regulates M1 to maintain a 5V BST voltage
across C4. A 10ꢀ resistor placed between SW and
BST cap is strongly recommended to reduce SW
spike voltage.
Figure 3: Internal Bootstrap Charging Circuit,
Startup and Shutdown
If both VIN and EN exceed 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.
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.
MP1495 Rev. 1.04
12/26/2012
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