Datasheet

CAT3637
http://onsemi.com
11
LED Current Setting
The current in each of the six LED channels is
programmed through the 1−wire EN/SET digital control
input. At the initial power−up and once the EN/SET is set
high, the LED current remains at zero in all channels. On the
first EN/SET pulse (positive edge), the current is set to 2 mA
in all channels. On each consecutive pulse, the current is
incremented by 2 mA. On the 15
th
pulse, the current is equal
to the full scale of 30 mA. On the following pulse (16
th
pulse), the current goes back to zero and the previous
sequence can be repeated. The EN/SET pin can be pulsed at
high frequency 15 times to decrement the current by 2 mA
or to program the current from 0 mA to 30 mA. The
maximum EN/SET signal frequency for programming the
LED current is 2.5 MHz.
To power−down the device and turn−off all current
sources, the EN/SET input should be kept low for a duration
T
OFF
of 1.5 ms or more. The driver typically powers−down
with a delay of about 1 ms.
Figure 24. EN/SET One Wire Addressable Timing Diagram
2 mA
4 mA
2 mA
0 mA0 mA
6 mA
28 mA
30 mA
Shutdown
EN/SET
LED
Current
Shutdown
T
D
T
HI
T
LO
T
OFF
Figure 25. EN/SET Program Increasing / Decreasing LED Current by 2 mA