CAT3643
LED Current Selection
LED current + 132
At power ? up, the initial LED current is set to full scale
(100% brightness) by the external resistor R SET as follows:
0.6 V
R SET
The EN/DIM pin has two primary functions. One function
enables and disables the device. The other function is LED
current dimming with six different levels by pulsing the
input signal, as shown on Figure 29. On each consecutive
pulse rising edge, the LED current is divided by half to 50%,
then 25%, 12.5%, 6.25% and 3.125% dimming levels.
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.
The LED driver enters a “zero current” shutdown mode if
EN/DIM is held low for 1.5 ms or more.
EN/DIM
T SETUP
T LED
100%
T HI
T LO
100%
T PWRDWN
LED
Current
Shutdown
50%
25%
12.5% 6.25%
3.12%
Shutdown
Figure 29. EN/DIM Digital Dimming Timing Diagram
Table 7. LED CURRENT DIMMING LEVELS
EN/DIM # of Pulses *
EN = High
1 st
2 nd
3 rd
4 th
5 th
6 th
x th
R SET Gain
132
66
33
16.5
8.25
4.125
132
Device cycling through gain selection
LED Current
132 x 0.6 V / R SET
66 x 0.6 V / R SET
33 x 0.6 V / R SET
16.5 x 0.6 V / R SET
8.25 x 0.6 V / R SET
4.125 x 0.6 V / R SET
132 x 0.6 V / R SET
GAIN x 0.6 V / R SET
* The gain is changed on the rising edges of the EN/DIM input.
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