MP1495S

– SYNCHRONOUS STEP-DOWN CONVERTER

MP1495S Rev. 1.0

www.MonolithicPower.com

11

12/13/2013

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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 MP1495S 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 10

Ω 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.