MP8757–18V, HIGH CURRENT SYNCHRONOUS BUCK CONVERTER

MP8757 Rev. 1.0

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15

5/1/2018

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and the low-side MOSFET turn on acting as an -

1A current source.

When the feedback voltage becomes lower than

60% of the target voltage, the UVP comparator

output goes high if the UV still occurs after 26us

delay; then the fault latch will be triggered---

latches HS off and LS on; the LS FET keeps on

until the inductor current goes zero. Also fault

latching can be reset by EN going low or Power-

cycling of VIN.

UVLO Protection

The

MP8757

has

under-voltage

lock-out

protection (UVLO). When the VCC voltage is

higher than the UVLO rising threshold voltage,

the part will be powered up. It shuts off when the

VCC voltage is lower than the UVLO falling

threshold voltage. This is non-latch protection. If

an application requires a higher under-voltage

lockout (UVLO), use the EN pin as shown in

Figure 9 to adjust the input voltage UVLO by

using two external resistors. It is recommended

to use the enable resistors to set the UVLO

falling threshold (VSTOP) above 4.5V. The rising

threshold (VSTART) should be set to provide

enough hysteresis to allow for any input supply

variations.

Figure 9

—Adjustable UVLO

Thermal Shutdown

Thermal shutdown is employed in the MP8757.

The junction temperature of the IC is internally

monitored. If the junction temperature exceeds

the threshold value (typical 150ºC), the converter

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

about

25ºC

hysteresis.

Once

the

junction

temperature drops to about 125ºC, it initiates a

SS.

Output Discharge

MP8757 discharges the output when EN=low, or

the controller is turned off by the protection

functions (UVP & OCP, OCP, OVP, UVLO, and

thermal shutdown). The part discharges the

output using an internal 6

Ω MOSFET.

EN Comparator

EN

MP8757

IN