CAT3648 Datasheet, PDF (10/14 Pages) Catalyst Semiconductor – 4-Channel Ultra High Efficiency Quad-Mode™ LED Driver with 32 Dimming Levels

CAT3648
LED Current Selection
After power-up, the LED current is set by the
external resistor (R_SET) value and the number of
pulses (n) on the EN/DIM input as follows:
LED current = 125 × ^0.6V × ⎜⎛ ^{31− n} ⎟⎞
R_{SET ⎝} 31 _⎠
The full scale current is calculated from the above
formula with n equal to zero.
The EN/DIM 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 3. On each consecutive pulse rising edge, the
LED current is decreased by about 3.2% (1/31^th of
the full scale value). After 30 pulses, the LED current
is 3.2% of the full scale current. On the 31^st pulse,
the current drops to zero, and then goes back to full
scale on the following pulse.
Each pulse width should be between 200ns and
100µs. 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 EN/DIM signal at high frequency, the
LED current can quickly be set to zero.
The LED driver enters a “zero current” shutdown
mode if EN/DIM is held low for 1.5ms or more.
The dimming level is set by the number of pulses on
the EN/DIM after the power-up, as shown in Table 2.
Table 2. Dimming Levels
Full Scale
Current in %
100
97
94
90
87
84
81
77
74
71
68
65
61
58
55
52
48
45
42
39
35
32
29
26
23
19
16
13
10
6
3
0
100
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
EN/DIM
T_LED
LED
Current
Shutdown
T_HI
T_LO
100%
97% _94%
32 Levels
3% _0%
100%
T_PWRDWN
Shutdown
Figure 3. EN/DIM Digital Dimming Timing Diagram
Doc. No. MD-5031, Rev. A
10
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice