MP4571 datasheet(24/34 Pages) MPS

24 / 34 page

MP4571

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

MP4571 Rev. 1.1

www.MonolithicPower.com

2/22/2023

MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.

when input voltage drops below the UVLO falling

threshold. This function prevents the device from

operating at an insufficient voltage. It is a non-

latch protection.

Over-Current Protection (OCP)

The MP4571 has a 1.95A peak current limit.

Once the inductor current reaches the current

limit, the HS-FET turns off immediately. Then the

LS-FET turns on to discharge the energy, and

the inductor current decreases. The HS-FET

does not turn on again until the inductor current

drops below the current threshold (the valley

current

limit).

This

protection

prevents

the

inductor

current

from

running

away

and

damaging the components.

Short-Circuit Protection (SCP)

When

short-circuit

condition

occurs,

the

MP4571 immediately reaches its current limit.

Meanwhile, the output voltage drops until VFB

falls below 50% of VREF. The device considers

this an output dead short, and triggers hiccup

short-circuit

protection

(SCP)

mode

periodically restart the part.

In hiccup mode, the MP4571 disables its output

power stage, slowly discharges the soft-start

capacitor, then initiates a soft start. If the short-

circuit condition remains after soft start ends, the

device repeats this operation until the short

circuit disappears and the output returns to the

regulation level. This protection mode greatly

reduces the average short-circuit current to

alleviate thermal issues and protect the regulator.

Negative Current Protection

The MP4571 has a -1.3A negative current limit.

Once the inductor current reaches the current

limit, the LS-FET immediately turns off and the

HS-FET turns on. The current limit prevents the

negative current from dropping too low and

damaging the components.

Thermal Shutdown

For thermal protection, the MP4571 monitors the

IC temperature internally. This function prevents

the chip from operating at exceedingly high

temperatures.

the

junction

temperature

exceeds the threshold value (about 170°C), it

shuts down the whole chip. This is a non-latch

protection. There is a 25°C hysteresis. Once the

junction temperature drops to about 145°C, the

device resumes operation by initiating a soft

start.

Floating Driver and Bootstrap Charging

An external bootstrap capacitor powers the

floating HS-FET driver. There are two methods to

charge the bootstrap capacitor (see Figure 3).

The first method is through the main charging

circuit from VCC through a diode. When the HS-

FET is on, VSW is about equal to VIN but exceeds

VCC, and the bootstrap capacitor is not charged.

The best charging period occurs when the LS-

FET is on, and VCC - VSW is at its largest. When

there is no current in the inductor, VSW equals

VOUT, so VCC can only charge BST when VOUT is

very small.

The second method is through the auxiliary

charging circuit from VIN. When the voltage

difference between BST and SW is below the

internal 5V bootstrap regulator, a PMOS pass

transistor (M1) turns on to charge the bootstrap

capacitor. The charging current is much smaller

than that from VCC, but as long as VIN exceeds

VSW, BST can be charged. This function is useful

in sleep mode, when there is not always a switch.

Figure 3: Internal Bootstrap Charging Circuit

Low-Dropout Operation (BST Refresh)

To improve dropout, the MP4571 is designed to

operate at close to 100% duty cycle as long as

the BST-to-SW voltage exceeds 1.4V. When the

BST-to-SW voltage drops below 1.34V, the HS-

FET turns off using a UVLO circuit, which allows

the LS-FET to conduct and refresh the charge on

the BST capacitor. When the input voltage drops,

the HS-FET remains on and close to 100% duty

cycle to maintain output regulation until the BST-

to-SW voltage falls below 1.34V.

Since the supply current sourced from the BST

capacitor is low, the HS-FET can remain on for

MP4571 Datasheet(PDF) 24 Page - Monolithic Power Systems

MP4571 Datasheet(HTML) 24 Page - Monolithic Power Systems

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34

Datasheet Download

Link URL