CAT3643 Datasheet, PDF (11/15 Pages) Catalyst Semiconductor – 3-Channel Ultra High Efficiency Quad-Mode TM LED Driver

CAT3643
LED Current Selection
At power−up, the initial LED current is set to full scale
(100% brightness) by the external resistor R_SET as follows:
LED current + 132
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.
T_SETUP
T_HI
T_PWRDWN
EN/DIM
T_LED
LED
Current
Shutdown
100%
T_LO
100%
50%
25% _{12.5% 6.25% 3.12%}
Figure 29. EN/DIM Digital Dimming Timing Diagram
Table 7. LED CURRENT DIMMING LEVELS
EN/DIM # of Pulses *
R_SET Gain
EN = High
132
1^st
66
2^nd
33
3^rd
16.5
4^th
8.25
5^th
4.125
6^th
132
x^th
Device cycling through gain selection
* The gain is changed on the rising edges of the EN/DIM input.
Shutdown
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
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