MP28257 –4A, 4.2V-TO-20V, FAST TRANSIENT, SYNCHRONOUS STEP-DOWN CONVERTER

MP28257 Rev 1.0

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11/8/2011

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so that the PG pin is pulled to GND before SS is

PG pin is pulled high after a 0.5ms delay.

PG pin will be pulled low.

Over-Current Protection (OCP) and Short-

Circuit Protection (SCP)

MP28257 has cycle-by cycle over-current limit

control. It monitors the inductor current during the

ON state. Once the inductor current exceeds the

current limit, the HS-FET turns off and the OCP

timer—set at 50μs—starts. The OCP triggers. If

the inductor current reaches or exceeds the

current limit every cycle if in those the 50μs, the

device enters latch-off mode

The MP28257 SCP triggers when dead shorts

occur—when the inductor current exceeds the

current limit and the FB voltage is lower than

MP28257 needs power cycle to restart after it

triggers OCP or SCP.

Over/Under-Voltage Protection (OVP/UVP)

MP28257 monitors the output voltage through a

resistor-divided FB voltage to detect over- and

under-voltage on the output. When the FB

triggers the OVP. Once it triggers the OVP, the

LS-FET is always on while the HS-FET is off. It

needs to power cycle to turn on again.

Conversely, the UVP triggers when the FB

UVP accompanies a drop in the current limit and

this results in SCP.

UVLO Protection

MP28257 has under-voltage lock-out (UVLO)

protection. The MP28257 powers up when the

input voltage exceeds the UVLO rising threshold

voltage. It shuts off when the input voltage falls

below the UVLO falling threshold voltage. This is

non-latch protection.

Thermal Shutdown

The MP28257 employs thermal shutdown by

internally monitoring the junction temperature of

the IC. If the junction temperature exceeds the

threshold value (typically 150°C), the converter

shuts off. This is non-latch protection. There is

about 25°C hysteresis. Once the junction

temperature drops around 125°C, it initiates a

soft start.