ADP5501 datasheet(10/28 Pages) AD

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ADP5501

Rev. 0 | Page 10 of 28

BACKLIGHT OPERATING LEVELS

Backlight brightness control can operate in three distinct levels:

daylight (L1), office (L2), and dark (L3). The BL_LVL bits in

The BL_LVL bits can be changed manually or, if in auto mode,

by the ambient light sensor (see the Ambient Light Sensing

section). By default, the backlight operates at daylight level

(BL_LVL = 00), where the maximum brightness is set using

also be set using Register 0x06 (DAYLIGHT_DIM). When oper-

ating at office level (BL_LVL = 01), the backlight maximum and

dim brightness settings are set by Register 0x07 (OFFICE_MAX)

and Register 0x08 (OFFICE_DIM). When operating at dark

level (BL_LVL = 10), the backlight maximum and dim

brightness settings are set by Register 0x09 (DARK_MAX) and

DAYLIGHT (L1)

OFFICE (L2)

DARK (L3)

BACKLIGHT OPERATING LEVELS

DAYLIGHT_DIM

DAYLIGHT_MAX

OFFICE_MAX

DARK_MAX

DARK_DIM

OFFICE_DIM

30mA

Figure 15. Backlight Operating Levels

BACKLIGHT MAXIMUM AND DIM SETTINGS

The backlight maximum and dim current settings are determined

by a 7-bit code programmed by the user into the registers listed

in the Backlight Operating Levels section. This 7-bit code allows

the user to set the backlight to one of 128 different levels between

0 mA and 30 mA. The ADP5501 can implement two distinct

algorithms to achieve a linear and a nonlinear relationship

between input code and backlight current. The BL_LAW bits, in

By default, the ADP5501 uses a linear algorithm (BL_LAW = 00),

where the backlight current increases linearly for a corresponding

increase of input code. Backlight current, in milliamperes (mA),

is determined by the following equation:

Backlight Current = Code × (Fullscale_Current/127)

(1)

where:

Code is the input code programmed by the user.

Fullscale_Current is the maximum sink current allowed

(typically, 30 mA).

The ADP5501 can also implement a nonlinear (square approx-

imation) relationship between input code and backlight current

level. In this case (BL_LAW = 01), the backlight current, in milli-

amperes (mA), is determined by the following equation:

127

⎟

⎠

⎞

⎜

⎝

⎛

Current

Fullscale

Code

Backlight Current =

(2)

Figure 16 shows the backlight current level vs. input code for

both the linear and square law algorithms.

128

SINK CODE

LINEAR

SQUARE

Figure 16. Backlight Current vs. Sink Code

BACKLIGHT TURN-ON/TURN-OFF/DIM

With the device in normal mode (set in Register 0x00 by

STNBY = 1), the backlight can be turned on using the BL_EN

bit in Register 0x00. Before turning on the backlight, the user

should choose the level (daylight (L1), office (L2), or dark (L3))

to operate in and ensure that maximum and dim settings are

programmed for that level. The backlight turns on when

BL_EN = 1. The backlight turns off when BL_EN = 0.

MAX

BL_EN = 1

BL_EN = 0

BACKLIGHT

CURRENT

Figure 17. Backlight Turn-On/Turn-Off

While the backlight is on (BL_EN = 1), the user can change it to

a dim setting by programming DIM_EN = 1 in Register 0x00. If

DIM_EN = 0, the backlight reverts to its maximum setting.

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