MP4012 ─ HIGH-VOLTAGE, HIGH-CURRENT ACCURACY WLED CONTROLLER

MP4012 Rev. 1.12

www.MonolithicPower.com

8

10/12/2013

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© 2013 MPS. All Rights Reserved.

OPERATION

The MP4012 drives external MOSFET with

current mode architecture to regulate the LED

current, which is measured through an external

current sense resistor. Figure 1 shows the

functional block diagram.

MP4012 employs a special circuit for regulating

the internal power supply, which covers a wide

input voltage from 8V to 55V. The 7.75V linear

regulator provides all the power for internal

circuits and external MOSFET gate drive energy.

MP4012 has a 2% accurate 1.25V reference,

which is used as the reference for LED current.

The reference is also used to set the current limit

and over voltage threshold.

MP4012 can be programmed as constant

switching frequency (CF) or constant off time (CT)

operation. Connecting a resistor between RT pin

and GND sets the switching frequency for CF

mode. Connecting a resistor between RT pin and

GATE pin sets the off time for CT mode. For

constant switching frequency mode, MP4012

includes a slope compensation section to ensure

the converter stability when duty cycle is greater

than 0.5.

For synchronization, the SYNC pins of multiple

MP4012 can be connected together, and may

also be connected to the open drain output of a

master clock. When connected in this manner,

the oscillators will lock to the device with the

highest operating frequency.

MP4012 has two high-speed current comparators.

One is used during normal operation, which

contains an internal 100ns blanking time to

prevent the current spike from mis-triggering the

comparator. The other is used to limit the

maximum switch current, which is programmable

by connecting a resistor divider from REF pin.

REF

VDD

R

Q

CS

CL

S

+

-

+

-

LEB

SL

Reset

VIN

GATE

FAULT

R

QN

Q

EN

S

+

-

5V

OVP

GND

SYNC

RT

-

+

FB

ISET

COMP

2

+

-

PWM

Linear Regulator

Oscillator

Hiccup Control

BandGap

Thermal

POR

Hiccup Done

Hiccup Done

POR

POR

POR

POR

EN

Hiccup Done

Reset

Hold

Hiccup

PWM blank

100k

Slope

Compensation

POR

Figure 1—Functional Block Diagram