MP4601 – WHITE LED DRIVER FOR LARGE SIZE TV BACKLIGHTING

MP4601 Rev. 1.0

www.MonolithicPower.com

11

1/28/2011

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© 2011 MPS. All Rights Reserved.

OPERATION

The MP4601 is a current mode regulator. The

sensing resistor senses the LED current and

feeds it back to an error amplifier, which

regulates

it

to

200mV

with

an

inside

compensation network. The COMP pin is the

output of the error amplifier. The inductor peak

current is proportional to the COMP pin voltage.

An increase of the COMP voltage increases the

current delivered to the output.

LED Open Protection

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

decreases sufficiently. System enjoys auto-

recovery for the LED open protection.

LED Short Protection

If the FB voltage is higher than 600mV,

immediately IC is latched off and DGD is pulled

low. If FB voltage is higher than 300mV for

480µs, IC is also latched off and DGD is pulled

low. The EN needs reset to restart the IC. The

Fault pin is pulled low when IC is latched off.

Dimming Control

The MP4601 allows both Analog and PWM

dimming. For analog dimming, when the

voltage on DIM is from 0.7V to1.5V, the LED

current will change from 0% to 100% of the

maximum LED current. If the voltage on DIM

pin is higher than 1.5V or DIM pin is floated,

maximum LED current will be generated.

For PWM dimming, a PWM signal with 100Hz

to 50kHz frequency, amplitude over 1.5V

should be applied to DIM pin.

For combined PWM and analog dimming to get

a further high dimming ratio, apply a 100Hz to

50kHz PWM signal with its amplitude from 0.7V

to 1.5V to DIM pin.

DIM pin floated will deliver the maximum LED

current.

At PWM dimming off interval, an internal switch

disconnects the COMP pin capacitor from the

output of the error amplifier. Therefore, the

COMP voltage is hold at PWM off interval. This

feature improves the response speed of the

LED current and helps to achieve high dimming

ratio.

Digital dimming can achieve over 1:1000

dimming ratio with DIM frequency less than

200Hz.