ADP5501 Analog Devices, ADP5501 Datasheet - Page 11

• 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

The maximum and dim settings can be set between 0 mA and
30 mA; therefore, it is possible to program a dim setting that is
greater than a maximum setting. For normal expected opera-
tion, the user should program the dim setting to less than the
maximum setting.
AUTOMATIC DIM AND TURN-OFF TIMERS
The user can program the backlight to dim automatically by
using the BL_DIMT timer in Register 0x03. The dim timer has
15 settings ranging from 10 sec to 2 min. The user should
program the dim timer before turning on the backlight. If
BL_EN = 1, the backlight turns on to its maximum setting, and
the dim timer starts counting. When the dim timer expires, the
internal state machine sets DIM_EN = 1, and the backlight goes
to its dim setting.
If the user clears the DIM_EN bit (or reasserts the BL_EN bit),
the backlight reverts to its maximum setting, and the dim timer
begins counting again. When the dim timer expires, the internal
state machine again sets DIM_EN = 1, and the backlight goes to
its dim setting. Reasserting BL_EN at any point during the dim
timer countdown causes the timer to reset and begin counting
again. The backlight can be turned off at any point during the
dim timer countdown by clearing BL_EN.
The user can also program the backlight to turn off automatic-
ally by using the BL_OFFT timer in Register 0x03. The off timer
has 15 settings ranging from 10 sec to 2 min. The user should
MAX
BACKLIGHT
DIM
CURRENT
BACKLIGHT
MAX
DIM
CURRENT
SET BY USER
SET BY INTERNAL STATEMACHINE
BL_EN = 1
DIM TIMER
RUNNING
Figure 18. Backlight Turn-On/Turn-Off/Dim
BL_EN = 1
DIM_EN = 1
Figure 19. Dim Timer
DIM_EN = 1
DIM_EN = 0
BL_EN = 1
OR
DIM TIMER
RUNNING
DIM_EN = 0
DIM_EN = 1
BL_EN = 0
BL_EN = 0
Rev. 0 | Page 11 of 28
program the off timer before turning on the backlight. If
BL_EN = 1, the backlight turns on to its maximum setting, and
the off timer starts counting. When the off timer expires, the
internal state machine clears the BL_EN bit, and the backlight
turns off.
Reasserting BL_EN at any point during the off timer count-
down causes the timer to reset and begin counting again. The
backlight can be turned off at any point during the off timer
countdown by clearing BL_EN.
The dim timer and off timer can be used together for sequential
maximum-to-dim-to-off functionality. With both the dim and
off timers programmed, if BL_EN is asserted, the backlight
turns on to its maximum setting. When the dim timer expires,
the backlight changes to its dim setting. When the off timer
expires, the backlight turns off.
LINEAR BACKLIGHT FADE-IN AND FADE-OUT
To counteract the abrupt effect on the eyes of near instant turn-
on and turn-off of the backlight, the ADP5501 contains timers
to facilitate smooth fading among the off, on, and dim states. By
default (BL_LAW = 00 in Register 0x02), the ADP5501
implements a fading scheme using the linear backlight code
algorithm (see Equation 1).
BACKLIGHT
MAX
DIM
CURRENT
MAX
SET BY USER
SET BY INTERNAL STATE MACHINE
BACKLIGHT
CURRENT
SET BY USER
SET BY INTERNAL STATE MACHINE
Figure 21. Dim and Off Timers Used Together
BL_EN = 1
DIM TIMER
RUNNING
BL_EN = 1 BL_EN = 0
Figure 20. Off Time
DIM_EN = 1
OFF TIMER
RUNNING
OFF TIMER
RUNNING
BL_EN = 0
ADP5501