AP3068 datasheet(11/15 Pages) BCDSEMI

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Preliminary Datasheet

WHITE LED DRIVER FOR LCD PANEL BACKLIGHT

AP3068

May. 2010

Rev. 1.3

BCD Semiconductor Manufacturing Limited

Application Information (Continued)

6. LED Current Setting

The maximum LED current per channel can be

adjusted up to 100mA via ISET pin. When ≥100mA

current is needed in application, two or more

channels can be paralleled to provide larger drive

current (Figure 10). Connect a resistor RISET between

ISET pin and GND to set the reference current ISET,

and ISET can be expressed as below:

ISET

SET

1.194V

This reference current is multiplied internally with a

gain (k) of 400, and then be mirrored onto all enabled

channels, which can set the maximum LED current,

referred to as 100% current (ICHX_MAX). And ICHX_MAX

can be expressed as below:

SET

CHX_MAX

The LED current can be reduced from 100% by

PWM dimming control.

7. PWM Dimming Mode

Applying a PWM signal to PWM pin to adjust the

LED current, that means, the LED current of all

enabled channels can be adjusted at the same time

and the LED brightness can be adjusted from 1%×

ICHX_MAX to 100% × ICHX_MAX. During the “high

level” period of PWM signal, the LED is turned on

and 100% of the current flows through LED, while

during the “low level” period of the PWM signal, the

LED is turned off and almost no current flows

through the LED, thus changing the average current

through LED and finally adjusting LED brightness.

The external PWM signal frequency applied to PWM

pin is allowed to be 100Hz or higher.

Figure 8. PWM Dimming of AP3068 (Example)

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