Datasheet

ADP5520
Rev. A | Page 10 of 40
DARK_MAX
DAYLIGHT_MAX
DAYLIGHT_DIM
OFFICE_MAX
OFFICE_DIM
DARK_DIM
MUX
BST
BL_VALUE
COUNTERS
AND
CONTROL
LOGIC
BL_DIMT
BL_FI
BL_FO
BL_OFFT
BL_EN
DIM_EN
BL_LAW
CLOCK
GENERATOR
BL_LVL
07445-005
BL_SNK
Figure 14. Backlight Brightness Control
BACKLIGHT OPERATING LEVELS
Backlight brightness control can operate in three distinct levels:
daylight (L1), office (L2), and dark (L3). The BL_LVL bits in
Register 0x02 control the level in which the backlight operates.
The BL_LVL bits can be changed manually, or if in automatic
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
Register 0x05 (DAYLIGHT_MAX). A daylight dim setting can
also be set using Register 0x06 (DAYLIGHT_DIM). When operat-
ing 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 Register 0x0A
(DARK_DIM).
DAYLIGHT (L1) OFFICE (L2) DARK (L3)
BACKLIGHT OPERATING LEVELS
BACKLIGHT CURRENT
07445-006
DAYLIGHT_DIM
DAYLIGHT_MAX
OFFICE_MAX
DARK_MAX
DARK_DIM
OFFICE_DIM
0
30mA
Figure 15. Backlight Operating Levels
BACKLIGHT MAXIMUM AND DIM SETTINGS
The backlight maximum and dim current settings are deter-
mined by a 7-bit code programmed by the user into the registers
listed in the Backlight Operating Levels section. This 7-bit
resolution allows the user to set the backlight to 1 of 128
different levels between 0 mA and 30 mA. The ADP5520 can
implement two distinct algorithms to achieve a linear and a
nonlinear relationship between input code and backlight
current. The BL_LAW bits in Register 0x02 are used to swap
between algorithms.
By default, the ADP5520 uses a linear algorithm (BL_LAW =
00), where backlight current increases linearly for a correspond-
ing increase of input code. Backlight current (in 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 ADP5520 can also implement a nonlinear (square approxima-
tion) relationship between input code and backlight current level.
In this case (BL_LAW = 01), the backlight current (in mA) is
determined by the following equation:
Backlight Current =
2
127
_
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
×
CurrentFullscale
Code (2)
Figure 16 shows the backlight current level vs. input code for
both the linear and square law algorithms.
07445-007
30
25
20
15
10
5
0
0 32 64 96 128
SINK CODE
BACKLIGHT CURRENT (mA)
LINEAR
SQUARE
Figure 16. Backlight Current vs. Sink Code