Datasheet

ADP5520
Rev. A | Page 18 of 40
The ADP5520 can also implement a nonlinear (square approxima-
tion) relationship between input code and LED sink current
level. In this case (LED_LAW = 1), the LED sink current (in
milliamps) is determined by the following equation:
LED Sink Current =
2
63
_
⎟
⎟
⎠
⎞
⎜
⎜
⎝
⎛
×
CurrentFullscale
Code (4)
Figure 41 shows the auxiliary LED sink current levels vs. input
code for both the linear and square law algorithms.
07445-030
0163248
CODE
LED SINK CURRENT (mA)
LINEAR
SQUARE
64
14
12
10
8
6
4
2
0
Figure 41. LED Sink Current vs. Code
Similar to the backlight current sink, the ADP5520 contains
timers to facilitate the smooth fading between off and on states
of the LED current sinks. All three LED sinks share a common
fade-in (LED_FI) timer as well as a common fade-out (LED_FO)
timer. The fade-in and fade-out timers are located in Register 0x13,
and can be programmed to one of 15 settings ranging from 0.3 sec
to 5.5 sec. Fade-in times represent the time it takes to fade from
0 mA to 14 mA. Fade-out times represent the time it takes to
fade from 14 mA to 0 mA. Fading between intermediate settings
is shorter. The fade timers should be programmed before
asserting LEDx_EN.
By default (LED_LAW = 0), the ADP5520 implements a fading
scheme using the linear algorithm (see Equation 3).
14
12
10
8
6
4
2
0
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
FADE-IN TIME (s)
07445-031
LED SINK CURRENT (mA)
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
Figure 42. Linear Fade-In Times
14
12
10
8
6
4
2
0
0 0.51.01.52.02.53.03.54.04.55.05.5
FADE-OUT TIME (s)
07445-032
LED SINK CURRENT (mA)
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
Figure 43. Linear Fade-Out Times
To achieve a more natural fading experience to the eye, the fade
timers can be used in conjunction with the square law approxima-
tion codes (see Equation 4) by setting LED_LAW = 1.
14
12
10
8
6
4
2
0
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
FADE-IN TIME (s)
07445-033
LED SINK CURRENT (mA)
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
0.3 SEC
0.6 SEC
0.9 SEC
1.2 SEC
1.5 SEC
1.8 SEC
Figure 44. Square Law Fade-In Times
14
12
10
8
6
4
2
0
0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5
FADE-OUT TIME (s)
07445-034
LED SINK CURRENT (mA)
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
Figure 45. Square Law Fade-Out Times