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

MP4012 Rev. 1.12

www.MonolithicPower.com

9

10/12/2013

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Start up

The start up process is shown in Figure 2.

During start up, the COMP is charged to 5V first,

then it is discharged by an internal current source,

MP4012 is active until the COMP voltage is

discharged to 1V. The high level Fault turns on

the external disconnected MOSFET. The output

current is regulated by the converter.

5V

VCC

Fault

COMP

1V

VIN

Iout

Figure 2—Start up Process

Analog Dimming

Analog dimming can be accomplished by varying

the voltage at the ISET pin. This can be done

either by using resistor divider from the REF pin

or by applying an external DC voltage at the

ISET pin.

PWM Dimming

PWM dimming can be achieved by applying a

square wave signal on PWM pin. The PWM

signal controls the internal error amplifier (EA),

FAULT output and GATE output. When the PWM

signal is high, the GATE and FAULT pins are

enabled, and the output of the EA is connected to

the external compensation network. So the LED

current is regulated accurately. When the PWM

signal goes low, the GATE signal is disable. And

the FAULT pin is pulled down to GND to turn off

the disconnecting MOSFET. Meanwhile the

output of the EA is disconnected from the

compensation network. Thus, the COMP voltage

can be hold by external capacitor. And the

disconnecting MOSFET can prevent the output

voltage from being discharged, which helps to

achieve the high frequency PWM dimming with

better linear dimming performance.

Protection

MP4012 includes short circuit protection and over

voltage protection, If the fault conditions are

detected (either short circuit or open circuit), the

COMP pin is disconnected from the internal EA

and the Gate and Fault pins are pulled down to

disable the LED controller, once the fault is

remove, the COMP pin is charged by an internal

current source until it reaches 5V, then the

COMP is discharged by an internal current

source. When it reaches 1V, the current source is

disconnected from COMP pin and the internal EA

is connected to it, the Fault pin starts to go high

and the Gate pin is allowed to switch.