MP4541

– 80V, 0.8A, SYNCHRONOUS STEP-DOWN CONVERTER

MP4541 Rev. 1.0

MonolithicPower.com

13

5/28/2021

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The switching frequency is typically set between

100kHz and 1MHz.

Power Supply

The

MP4541’s control circuit is powered by VCC,

which is regulated by VIN.

There is a VCC under-voltage lockout (UVLO)

circuit that protects the MP4541 from operating

at an insufficient VIN. The MP4541’s UVLO

comparator monitors VCC and starts operating

when VCC exceeds the VCC UVLO rising

threshold.

Start-Up

When the EN pin is high and VCC exceeds its

UVLO threshold, the MP4541 starts up via an

internal soft-start (SS) signal. Once the MP4541

starts switching, the SS signal ramps up from 0V

and is compared to VREF. The lower voltage is

used by the error amplifier (EA) to control VOUT.

After the SS signal exceeds VREF, soft start

completes, and the internal reference block

regulates the feedback loop.

The MP4541 is designed for monotonic start-up

into pre-biased loads. If the output is pre-biased

to a certain voltage during start-up, the voltage

on the SS capacitor is charged. If the SS

capacitor voltage exceeds the sensed output

voltage

at

FB,

the

device

starts

normal

operation.

Enable (EN) and Configurable Under-Voltage

Lockout (UVLO)

The EN pin turns the MP4541 on and off. If

voltage above 0.9V is applied, the MP4541 starts

the internal bandgap (BG) circuit. Once the EN

voltage (VEN) exceeds EN’s high threshold

(typically 1.25V), the MP4541 turns on all

functions

and

starts

switching

operation.

Switching operation stops once VEN drops below

the low threshold (typically 1.13V). EN is

compatible with voltages up to 80V.

There is no internal resistor on EN. For

automatic start-up, connect EN to VIN through a

resistor.

Overload Protection (OLP) and Short-Circuit

Protection (SCP)

The MP4541 features valley current limit control.

The inductor current is monitored during the

LS-FET

’s on state. When the inductor current

exceeds the valley current limit threshold, the

LS-FET current limit comparator output switches.

The HS-FET remains off until the inductor

current drops below the valley current limit. Then

the HS-FET turns on again. Meanwhile, the FB

output voltage (VFB) may drop below its UVLO

threshold (typically 60% of VREF). Once UVLO is

triggered, the MP4541 enters hiccup mode and

periodically restarts the part. Hiccup mode is

disabled during soft start.

If over-current protection (OCP) triggers hiccup

mode, the MP4541 turns off the output power

stage and discharges the SS capacitor. Then the

IC automatically initiates another soft start. If the

over-current (OC) condition remains after soft

start ends, the device repeats this hiccup

operation until the OC condition is removed.

Once the OC condition has been removed, VOUT

returns to the regulation level.

Bootstrap (BST) Power Supply

An external bootstrap (BST) capacitor powers

the floating MOSFET driver. The external BST

capacitor is charged by VCC. The VBST - VSW

voltage supplies power to the HS-FET driver.

The MP4541 turns on once both VCC and EN

exceed

their

respective

thresholds.

The

reference block turns on first, and generates a

stable VREF and reference currents. Then the

internal

regulator

turns

on.

The

regulator

provides a stable supply for the remaining

circuits.

Three events can shut down the chip: EN being

pulled low, VCC being pulled low, and thermal

shutdown. The shutdown procedure starts by

blocking the signaling path to avoid any fault

triggering. Then the COMP voltage (VCOMP) and

the internal supply rail are pulled low. The BST

floating driver is not subject to this shutdown

command.

Thermal Shutdown Protection

The MP4541 has one circuit to monitor the

temperature. If the junction temperature exceeds

150°C, the MP4541 shuts down. Once the

temperature drops below 125°C, the device

resumes normal operation.