ADP5501 Analog Devices, ADP5501 Datasheet - Page 13

• 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

FADE OVERRIDE
A fade override feature allows the BL_FI and BL_FO timers to
be overridden when the BL_EN bit is reasserted (by the user
setting the FOVR bit in Register 0x02) during a fade-in or fade-
out period and to set the backlight to its maximum setting.
ADVANCED FADING (SQUARE)
Although the default linear fade algorithm gives a smooth
increase and decrease in backlight current, the resulting
increase and decrease in brightness still appear visually abrupt.
For example, for a given fade-in time, the eye notices an initial
increase in brightness as backlight current is increased but
cannot perceive much more increase in brightness as backlight
current is increased to maximum.
The reason for this is that the eye perceives changes in light
when the brightness of the light source is changed logarithmically
(Weber-Fechner law). To provide a more natural fading exper-
ience to the user, the fade timers can be used in conjunction with
the square law approximation backlight codes (see Equation 2)
by setting BL_LAW = 01 in Register 0x02.
MAX
BACKLIGHT
CURRENT
BL_EN = 1
30.0
27.5
25.0
22.5
20.0
17.5
15.0
12.5
10.0
7.5
5.0
2.5
(REASSERTED BY USER )
0
0
OVERRIDDEN
0.5
BL_EN = 1
FADE-IN
Figure 27. Square Law Fade-In Times
1.0
1.5
Figure 26. Fade Override
2.0
FADE-IN TIME (Sec)
BL_EN = 0
(REASSERTED BY USER)
2.5
OVERRIDDEN
FADE-OUT
BL_EN = 1
3.0
3.5
0.3 SEC
0.6 SEC
0.9 SEC
1.2 SEC
1.5 SEC
1.8 SEC
BL_EN = 0
4.0
4.5
2.1 SEC
2.4 SEC
2.7 SEC
3.0 SEC
3.5 SEC
4.0 SEC
4.5 SEC
5.0 SEC
5.5 SEC
5.0
5.5
Rev. 0 | Page 13 of
ADVANCED FADING (CUBIC 1 AND CUBIC 2)
Two additional advanced settings in Register 0x02 are available
for fading the backlight brightness levels, Cubic 1 (BL_LAW = 10)
and Cubic 2 (BL_LAW = 11). As shown in the backlight bright-
ness control block diagram in Figure 14, linear fading and
square fading are implemented by ramping the 128 linear/square
algorithm codes at a fixed frequency over the duration of a
given fade-in/fade-out time.
Cubic fading is implemented by re-using the square algorithm
codes but ramping them with a clock source whose frequency
output increases as the sink current code increases (see Figure 29).
Cubic 1 and Cubic 2 have different frequency vs. code charac-
teristics.
DAYLIGHT_MAX
28
DAYLIGHT_DIM
OFFICE_MAX
OFFICE_DIM
DARK_MAX
DARK_DIM
30.0
27.5
25.0
22.5
20.0
17.5
15.0
12.5
10.0
BL_LVL
7.5
5.0
2.5
0
0
Figure 29. Backlight Brightness Control (Cubic)
0.5
Figure 28. Square Law Fade-Out Times
1.0
MUX
1.5
BL_OFFT
BL_DIMT
FADE-OUT TIME (Sec)
BL_FO
BL_FI
2.0
BST
2.5
3.0
COUNTERS
BL_VALUE
CONTROL
3.5
LOGIC
AND
4.0
4.5
ADP5501
0.3 SEC
0.6 SEC
0.9 SEC
1.2 SEC
1.5 SEC
1.8 SEC
2.1 SEC
2.4 SEC
2.7 SEC
3.0 SEC
3.5 SEC
4.0 SEC
4.5 SEC
5.0 SEC
5.5 SEC
GENERATOR
5.0
BL_LAW
DIM_EN
CLOCK
BL_EN
BL_SNK
5.5