MP1494 – SYNCHRONOUS STEP-DOWN CONVERTER
circuit current is greatly reduced to alleviate
thermal issues and to protect the regulator. The
MP1494 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 reaches temperatures that
exceed 150°C, it shuts down the whole chip.
When the temperature is less than 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. This
UVLO’s rising threshold is 2.2V with a
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 will regulate 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.
D1
V
IN
M1
BST
R4
U1
5V
C4
V
OUT
SW
L1
C2
Figure 3: Internal Bootstrap Charging Circuit,
Startup and Shutdown
If both VIN and EN exceed their respective
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 a 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.
MP1494 Rev. 1.04
12/26/2012
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