CAT3644_0710 Datasheet, PDF (10/14 Pages) Catalyst Semiconductor – 4-Channel Ultra High Efficiency Quad-Mode™ LED Driver

CAT3644
LED Current Selection
At power-up, the initial LED current is set to full scale
(100% brightness) by the external resistor RSET as
follows:
LED current = 132 × ^0.6V
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 3.
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 mini-
mum 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 1.5ms 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 3. EN/DIM Digital Dimming Timing Diagram
Table 1. 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
* The gain is changed on the rising edges of the EN/DIM input.
LED Current
132 × 0.6V R_SET
66 × 0.6V R_SET
33 × 0.6V R_SET
16.5 × 0.6V R_SET
8.25 × 0.6V R_SET
4.125 × 0.6V R_SET
132 × 0.6V R_SET
GAIN × 0.6V R_SET
Shutdown
Doc. No. MD-5023, Rev. E
10
© Catalyst Semiconductor, Inc.
Characteristics subject to change without notice