MP4569―75V, 0.3A, SYNCHRONOUS STEP-DOWN CONVERTER

MP4569 Rev. 1.0

www.MonolithicPower.com

10

9/12/2014

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OPERATION

The MP4569 is a 75V, 0.3A, 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, 0.3A output. It features a wide

input voltage range, external soft-start control,

and precision current limit. Its very low

operational quiescent current makes it suitable

for battery-powered applications.

Control Scheme

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, 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 zero. If

HS_FET turns on at once and commences

drops below 1V.

Ipeak

Io increase

Figure2 - Control Scheme

Internal Regulator and BIAS

The 2.6V internal regulator powers most of the

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

supply overrides the input voltage and supplies

it can power LS_FET 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 can be used to power BIAS.

Enable Control

The MP4569 has a dedicated enable-control pin,

disables the chip. This is HIGH logic. Its trailing

threshold is a consistent 1.2V. Its rising threshold

is about 350mV higher. When floating, EN pin is

internally pulled down to GND 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 shutdown mode 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 6.5V. 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 150μA. Just

note that there is an internal 3M resistor from EN

to GND, so the external pull up resistor should be

smaller than

1.55V

3M

1.55V]

-

[V

(MIN)

IN

×

to make sure

the part can EN on at the lowest operation VIN.