MP4568

―60V, 100mA, SYNCHRONOUS STEP-DOWN CONVERTER

MP4568 Rev. 1.01

www.MonolithicPower.com

10

8/18/2013

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© 2013 MPS. All Rights Reserved.

OPERATION

The MP4568 is a 60V, 100mA, synchronous,

step-down switching regulator with integrated

high-side

and

low-side

high-voltage

power

MOSFETs (HS_FET and LS_FET, respectively).

It provides a highly-efficient, 100mA output. It

features

a

wide

input

voltage

range,

internal/external soft-start control, and precision

current limit. Its very low operational quiescent

current makes it suitable for battery-powered

applications.

PWM Control

The ILIM comparator, FB comparator and zero

current detector (ZCD) block control the PWM. If

current drops to zero, HS-FET turns on and the

ILIM comparator starts to sense the HS-FET

current: When the HS-FET current reaches the

limit set by the ILIM pin, or FB reaches the OVP

threshold, the HS-FET turns off and LS-FET

turns on together with the ZCD block. Meanwhile,

the ILIM comparator is turned off to reduce the

quiescent current. The LS-FET turns off together

with ZCD block after the inductor current drops to

time,

the

HS-FET

turns

on

at

once

and

than 1V reference, HS-FET would not turn on till

Ipeak

Io increase

Figure 2

– PWM Control

Internal Regulator and BIAS

The 2.6V internal regulator powers most of the

than 3.0V, the output of the regulator is in full

output voltages.

input voltage and supplies power to the 2.6V

LS driver furthermore. Using BIAS to power

internal regulator can improve the efficiency. It is

recommended to connect BIAS to the regulated

output voltage when it is in the range of 2.9V to

5.5V. When output voltage is out of above range,

an external supply that is >2.9V or even better

>4.5V is needed to power BIAS.

Enable Control

The MP4568 has a dedicated enable-control pin,

disables the chip. This is HIGH effective logic. Its

trailing threshold is 1.2V typically and its rising

threshold is about 400mV higher. When floating,

EN pin is internally pulled down to GND through

a 2M resistor to disable the chip.

When EN = 0V, the chip goes into the lowest

shutdown-current mode. When EN is higher than

zero but lower than its rising threshold, the chip

remains in a shutdown mode but with a slightly

larger shutdown current.

Internally a zener diode is connected from EN pin

to GND pin. The typical clamping voltage of the

zener diode is 7.5V. So VIN can be connected to

EN through a high ohm resistor if the system

doesn't have another logic input acting as enable

signal. The resistor needs to be designed to limit

the EN pin sink current less than 100μA. Just

note that there is an internal 2M resistor from EN

to GND, so the external pull up resistor should be

smaller than

1.6V

2M

1.6V]

-

[V

(MIN)

IN



to make sure the

part can EN on at the lowest operation VIN.