ADP5501 Analog Devices, ADP5501 Datasheet - Page 10

• Manufacturer Part Number: ADP5501
• Description: Programmable Current Backlight Driver with Ambient Light Sensor Input
• Manufacturer: Analog Devices

Specifications of ADP5501

• Vin Range: 2.7 to 5.5V
• Vout (v): 24 to 27
• Synchronous: No
• Package: 24-Lead LFCSP
• Led Configuration: Serial
• Topology: Inductive
• I2c Support: Yes
• Max Iout (ma): 30mA
• Brightness Control: I2C
• Switching Frequency: 1MHz
• Over Volt Protection (v): 24V

ADP5501
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 at which the backlight operates.
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
Register 0x05 (DAYLIGHT_MAX). A daylight dim setting can
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
Register 0x0A (DARK_DIM).
30mA
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
Register 0x02, are used to swap between algorithms.
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:
where:
Code is the input code programmed by the user.
Fullscale_Current is the maximum sink current allowed
(typically, 30 mA).
0
DAYLIGHT_MAX
Backlight Current = Code × (Fullscale_Current/127)
DAYLIGHT (L1)
DAYLIGHT_DIM
Figure 15. Backlight Operating Levels
BACKLIGHT OPERATING LEVELS
OFFICE_MAX
OFFICE (L2)
OFFICE_DIM
DARK_MAX
DARK (L3)
DARK_DIM
Rev. 0 | Page 10 of 28
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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:
Figure 16 shows the backlight current level vs. input code for
both the linear and square law algorithms.
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.
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.
Backlight Current =
BACKLIGHT
MAX
CURRENT
30
25
20
15
10
5
0
0
Figure 16. Backlight Current vs. Sink Code
BL_EN = 1
Figure 17. Backlight Turn-On/Turn-Off
32
LINEAR
⎛
⎜
⎜
⎝
Code
SINK CODE
64
×
SQUARE
Fullscale
BL_EN = 0
127
96
_
Current
128
⎞
⎟
⎟
⎠
2
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