MP4603 – WHITE LED DRIVER FOR LARGE SIZE TV BACKLIGHTING

MP4603 Rev. 1.0

www.MonolithicPower.com

10

4/27/2012

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© 2012 MPS. All Rights Reserved.MP4603

OPERATION

The MP4603 is a current mode regulator. The

sensing resistor senses the LED current and the

signal goes an error amplifier, which regulates it

to 200mV through an internal compensation

network—The COMP pin is the output of the

error amplifier. The inductor peak current is

proportional to the COMP voltage. Increasing the

COMP voltage increases the current delivered to

the output.

LED Open Protection

If the LED is open, there is no voltage on the FB

reaches the shutdown threshold. The top switch

turns off, and the IC latches off. At LED open

protection, the Fault pin goes low.

LED Short Protection

If the FB voltage exceeds 600mV, the IC

immediately latches off and DGD goes low. If the

FB voltage exceeds 300mV for around 450µs, IC

latches off and DGD goes low. The EN pin must

reset to restart the IC. The Fault pin goes low

when the IC latches off.

Dimming Control

The MP4603 allows for both Analog and PWM

dimming. The analog dimming voltage range on

ADIM goes from 0V to1.2V to change the LED

current from 0% to 100% of the maximum LED

current. If the voltage on the ADIM pin exceeds

1.2V or is floating, LED current goes to its

maximum.

PWM dimming uses a square-wave signal with a

100Hz-to-50kHz

frequency

range

and

an

amplitude over 2.2V applied to the PWM pin.

PWM dimming can achieve over 1:1000 dimming

ratio with PWM frequency less than 200Hz

During the PWM dimming OFF interval, an

internal switch disconnects the COMP pin

capacitor from the output of the error amplifier:

This holds the COMP voltage during the PWM

OFF interval and increases the LED current

response speed to achieve a high dimming ratio.

Combine PWM and analog dimming to increase

the dimming ratio. Apply a 100Hz to 50kHz PWM

signal on PWM pin and a analog dimming signal

in range of 0V to 1.2V on ADIM pin.

.