Arduino Forum

Using Arduino => General Electronics => Topic started by: mttgwh on Jul 11, 2011, 05:55 pm

Title: A question about TLC5940
Post by: mttgwh on Jul 11, 2011, 05:55 pm
:)HI!

I would like to use TLC5940 with Arduino to create something,
but I don't understand the following figure:
http://students.washington.edu/acleone/codes/tlc5940arduino/img/breadboard-arduino-tlc5940.png
from(http://www.arduino.cc/playground/Learning/TLC5940)
Why It's 39.06???
Where 39.06 come from?

Thanks a lot!!!
Title: Re: A question about TLC5940
Post by: MarkT on Jul 12, 2011, 03:24 am
Since the accuracy is only +/-13% or so anyway, that figure should be 40, 4 digits of precision is utterly unwarranted!

The way the chip works is that the output current is set by a current mirror with a nominal gain of 31.5, and the reference current is set by the resistor from an on-chip 1.24V voltage reference. 31.5 x 1.24 ~= 39

The 31.5 figure probably represents linear proportions of the relevant transistors' channel width on the silicon of 63:2