MP4571

– 60V, 1A, SYNCHRONOUS STEP-DOWN CONVERTER

MP4571 Rev. 1.1

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25

2/22/2023

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more switching cycles than are required to

refresh the capacitor. The means the effective

duty cycle of the switching regulator is high.

The effective duty cycle during regulator dropout

is mostly influenced by the voltage drops across

the power MOSFET, inductor resistance, low-

side diode, and PCB resistance.

Start-Up and Shutdown

If both VIN and VEN exceed their respective

thresholds, the chip starts. The reference block

starts first, generating a stable reference voltage

and current, and then the internal regulator is

enabled. The regulator provides a stable supply

for the remaining circuitries.

While the internal supply rail is up, an internal

timer holds the power MOSFET off for about

50µs to blank the start-up glitches. When the

soft-start block is enabled, it first holds its SS

output low to ensure the circuitries are ready,

then slowly ramps up.

Three events can shut down the chip: EN going

low, VIN UVLO, and thermal shutdown. In the

shutdown

procedure,

the

signaling

path

is

blocked first 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, but its

charging path is disable.