MP8761 — 8A, 18V, SYNCHRONOUS STEP-DOWN CONVERTER

MP8761 Rev. 1.1

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16

11/4/2013

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negative current limit, the LS-FET turns OFF

immediately and stays OFF for the reminder

for the OFF period. In this situation, both

MOSFETs are OFF until the end of a fixed

interval. The HS-FET body diode conducts

the inductor current for the fixed time.

Over-Voltage Protection (OVP)

The MP8761 monitors the output voltage using

the FB pin connected to the tap of a resistor

divider.

If the FB voltage exceeds the nominal REF

voltage but remains below 120% of the REF

voltage (0.611V), both MOSFETs are OFF.

If the FB voltage exceeds 120% of the REF

voltage but remains below 130%, the LS-FET

turns ON while the HS-FET remains OFF. The

LS-FET remains ON until the FB voltage drops

below 110% of the REF voltage or the low-side

negative current limit triggers.

If the FB voltage exceeds 130% of the REF

voltage, the device enters a non-latch OFF mode.

Once the FB voltage rises to a reasonable value,

it will exit OVP and operate normally.

UVLO protection

The MP8761 has under-voltage lockout (UVLO).

When the VCC voltage exceeds the UVLO-rising

threshold, the MP8761 powers up. It shuts OFF

when the VCC voltage falls below the UVLO

falling threshold. This is non-latch protection.

The MP8761 is disabled when the VCC voltage

falls below 3.4V. If an application requires a

higher UVLO threshold, use the two external

resistors connected to the EN pin as shown in

Figure 9 to adjust the startup input voltage. For

best results, use the enable resistors to set the

enough hysteresis to account for any input

supply variations.

EN Comparator

IN

EN

Figure 9: Adjustable UVLO

Thermal Shutdown

The MP8761 has thermal shutdown. The IC

internally monitors the junction temperature. If

the junction temperature exceeds the threshold

value (minimum 150°C), the converter shuts off.

This is a non-latch protection. There is ~25°C

hysteresis. Once the junction temperature drops

to ~125°C, it initiates a soft-start.