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BD6583MUV-A

White Backlight LED Driver for Medium to Large LCD Panels (Switching Regulator Type)

ROHM Semiconductor 

BD6583MUV-A

Technical Note

●Brightness control

There are two dimming method is available, first method is analog dimming that apply analog voltage to ISET terminal, and

second method is PWM control via digital dimming of PWMPOW or PWMDRV. Because each method has the different merit,

please choose a suitable method for the application of use.

Two techniques can be used as digital dimming by the PWM control One is PWM control of current driver, the other is PWM

control of power control.

As these two characteristics are shown in the below, selects to PWM control process comply with application.

•Efficiency emphasis in the low brightness which has an influence with the battery life

•LED current dispersion emphasis in the PWM brightness control

 2) Power control PWM control

 1) Current driver PWM control

(Reference)

PWM regulation process

Current driver

Power control

Efficiency of LED current 0.5mA

(PWM Duty=2.5%)

70%

93%

PWM frequency 200Hz

Limit dispersion capability of low duty

0.2%

0.5%

1) Current driver PWM control is controlled by providing PWM signal to PWMDRV, as it is shown Fig.40.

The current set up with ISETH is chosen as the H section of PWMDRV and the current is off as the L section. Therefore, the

average LED current is increasing in proportion to duty cycle of PWMDRV signal. This method that it lets internal circuit and

DC/DC to work, because it becomes to switch the driver, the current tolerance is a few when the PWM brightness is adjusted,

it makes it possible to brightness control until 20µs (MIN0.4% at 200Hz). And, don't use for the brightness control, because

effect of ON/OFF changeover is big under 20µs ON time and under 20µs OFF time. There is no effect of ON/OFF

changeover at 0% and 100%, so there is no problem on use. Typical PWM frequency is 100Hz~10kHz. When resistance is

set as ISET, RSTB sets H  L, so the starting current may be effective, after RSTB sets L  H, it becomes PWM of the

starting current and PWM of ISETH setting current to PWM two times.

PWMDRV

ON

OFF

LED current

ON

OFF

Coil current

ON

OFF

IC’s active current

ON

Fig.40

2) Power control PWM control is controlled by providing PWM signal to PWMPOW, as it is shown Fig.41. The current setting

set up with PWMDRV logic is chosen as the H section and the current is off as the L section. Therefore, the average LED

current is increasing in proportion to duty cycle of PWMPOW signal. This method is, because IC can be power-off at

off-time, the consumption current can be suppress, and the high efficiency can be available, so it makes it possible to

brightness control until 50µs (MIN1% at 200Hz). And, don't use for the brightness control, because effect of power

ON/OFF time changeover is big under 50µs ON time and under 50µs OFF time. There is no effect of ON/OFF changeover

at 0% and 100%, so there is no problem on use.

Typical PWM frequency is 100Hz~1kHz. Also, PWM can't control RSTB and PWMPOW at the same time.

After RSTB sets H, control PWM only PWMPOW.

PWMPOW

ON

LED current

ON

Coil current

ON

IC’s active current

ON

OFF

OFF

OFF

OFF

Fig.41

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© 2011 ROHM Co., Ltd. All rights reserved.

14/26

2011.06 - Rev.C

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