CAT3649 Datasheet, PDF (10/14 Pages) ON Semiconductor – 6-Channel Quad-Mode LED Driver with 32 Dimming Levels & PWM

CAT3649
Current Selection
After power−up and once enabled, the LED current is set
initially to the full scale of 25 mA. The number of pulses (n)
on the ADIM input decreases the current value as follows:
ǒ Ǔ _{LED current [mA] + 25}
32 * n
32
(eq. 1)
The full scale current is calculated from the above formula
with n equal to zero.
The ADIM pin has two primary functions. One function
enables and disables the device. The other function is LED
current dimming with 32 different levels by pulsing the input
signal, as shown on Figure 28. On each consecutive pulse
rising edge, the LED current is decreased by about 3.1%
(1/32^th of the full scale value). After 31 pulses, the LED
current is 3.1% of the full scale current (lowest level). On the
following pulse, the LED current goes back to full scale.
Each pulse width should be between 200 ns and 100 ms.
Pulses faster than the minimum T_LO may be ignored and
filtered by the device. Pulses longer than the maximum T_LO
may shutdown the device. By pulsing the ADIM signal at
high frequency, the LED current can quickly be set to zero.
The LED driver enters a “zero current” shutdown mode if
ADIM is held low for longer than 30 ms.
The dimming level is set by the number of pulses on the
ADIM after the power−up, as shown in Table 6.
Table 6. DIMMING LEVELS
LED Current (Typical) [mA]
25.0
24.2
23.4
22.6
21.8
21.0
20.2
19.4
18.6
17.8
17.0
16.2
15.3
14.6
13.8
13.0
12.3
11.5
10.7
9.9
9.1
8.3
7.5
6.7
5.9
5.1
4.3
3.6
2.7
2.0
1.2
0.4
25
Dimming Pulses [n]
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
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