tlc5940 again

Forum 2005-2010 (read only) Hardware Interfacing
1

hello,
I'm wondering if somebody, who used successfull jims tlc5940 example, could give me an advise how to connect the tlc5940(DIL) correctly....in my version the tlc gets really hot;) I guess, tooo hot, as well the 16 LEds don't work properly:

This is the way I did:
all LEDs (red ones à 20mA) with anode over 150ohm to Vcc (4.5 V)
and with cathode to pins 1-15 & 28
the following jims code example:
VPRG --> Pin 8 (arduino 168)
SIN --> Pin 7
SCLK --> 6
Xlat --> 5
Blank --> 9
DCPRG --> 4
SOUT --> 3
Xerr --> 2

IREF over 200 Ohm to GND (1,24/0,2x31,5 = 195,3)

I dident put the 100nF condenser between Vcc and Gnd, and I dident put a Push-up Resistor 100k to Xerr....
I feed the leds and the tlc 5940 with the same Vcc source; 4,5 V and - probably much tooo less - 1A (16x0,2A =3,2A)....

But why then is not my powersupply getting hot?
any suggestions?
Thanks a lot for any help!
sibylle

2

hi

how did you figure out he resistor value for Iref? According to page 10 of the datasheet it should be about 2000 ohms, not 200. 200 ohms will give 120 ma per channel. Aslo, you don't need resistors in line with each resistor, as the chip does automatic current limiting ( fix the Iref resistor value first :slight_smile: )

D

PS: don't leave out the filter caps, it will cause problems.

3

thanks;)
now I see as well the 2000 in figure 3;) but I was calculating the resistor referring the formula on page 12 (1,24/0,2x31,5 = 195,3) ? but obvisouly I was missunderstanding something completely....

thanks again! and yes I will put all filters:)
sibylle