Need help with TLC5925 problem

I have connected 8- TLC5925 ICs (LOW-POWER 16-CHANNEL CONSTANT-CURRENT LED SINK DRIVER ) in a row, each TLC5925 drives 16 LED so i have a STATIC display with 8x16=128 LED.

TLC5925 needs 4 pins to work CLK,LE,OE,SDI, it is actually the same with the common 595 but it only needs a resistor for constant current to leds.
the problem now:
i connected to arduino and it works only IF i turn on ( i am using shiftout syntax) about 1/4 of the leds! if i try to light one more (after trying one more each time) then it stop working. it seems that arduino is restarting-trying to turn them on-restarting. again and again.(i can see them turn on for some milliseconds in my eyes and then turn off, this happends all time)

i noticed that led13 is flashing too so i think that arduino is shuting down when it is trying to turn them on.

From all these i think that the problem is somewhere in current, but i dont know what to do.

I have tried on duemialnove,MEGA,and at stand alone, but the problem still exist.

i connected a polymeter on vin and gnd and it gets 5v all time (and when it is restarting)

and something important that may help, i have 2 atmega 328 stand alone connected with 1 common regular L78L05, i noticed that both chips are restarting ( i am using only the one) so from this it seems that somehow there is problem on supply?

Any help? please.

sorry for my bad english

So how much supply decoupling do you have? I suspect none.

oh...none!! is the problem becouse that?

what can choose? ihave some 22pf/50v is that ok?
edit:mmm datasheet says 10pf..
i dont have at that time, can i try with 22pf?

edit: i tried with 22pf and the problem still exist

Any help please?

ihave some 22pf/50v is that ok?


have you not read the link I posted earlier? Use 0.1uF ceramic capacitors on each IC.

i dont have at that time

That doesn't change the laws of physics.
Using a capacitor that is 10000 times smaller than recommended is not going to have much effect.

Are you using an external supply or trying to power this entire project off the Arduino board?

Are you using an external supply or trying to power this entire project off the Arduino board?

i have tried both

have you not read the link I posted earlier? Use 0.1uF ceramic capacitors on each IC.

ok, tomorrow i will buy, i just wanted to know if this is the real reason...

i just wanted to know if this is the real reason

Who can tell if it is all the reasons but it certainly is one of them.

and this could make the arduino to shut down?

Yes it could cause the arduino to reset.

and couse to reset the stand alone atmel 328?

mmmm question, i have connected all "blank" pins together, is this correct?or only the first need to be connected to gnd?

What sort of Library are you using, the blank pin needs to be connected to one of the arduino pins in the standard TLC5490 library, it says in the header:-

The TLC5940 library uses the PWM output ability of digital pins 3, 9, 10, and 11.

with pin 10 being connected to the blank pin (23 of the TLC)
You still need decoupling though.

5925 is not using PWM

Sorry wrong chip.
What pin is the blank one?
Is it pin 21 output enable? If it is all of them should be connected to ground.

finally it works!!

and the reason is as you said decoupling capacitors!! really thanks

1 question now my PCBs that i have designed have 16x8 LED with 8 TLC5925, they have 8 slots for capacitors, one for each IC,

do i need to add some electrolytic capacitors between 3-4 ICs? my PCB have not any more space (holes) for more,

can i replace some of 0.1uf with electrolytic capacitors? for example

1-1-1-2-1-1-1-2 (where 1 is 0.1uf and where 2 is electronic 100[ch956]F)

any recomendation? and just to know the project is cascadable, i want to be able to connect many PCBs in a row (big display)

Yes I would replace one of the 0.1uF capacitors for an electrolytic. Especially if you are going to extend it. An electrolytic handles the low frequency noise and improves the supply impedance especially when the power is a long run from the supply.
It also might be a good time to get into surface mount components because the best sort of decoupling would be a surface mount ceramic that would sit nicely on the under side of the board between pins 1 and 24. All you need is a pair of tweezers and a fine point soldering iron.

Hi There,

I’m trying to control a TLC 5925 on my arduino uno. But I can’t get it to run at all. I think I got all parameters right and tried to follow the description in the datasheet precisely, but the driver doesn’t turn on any LEDs.

@acmiilangr: Could you please send me a short source code example how you control the TLC. I tried both methods, controlling the TLC through the SPI-library and controlling the TLC using raw data, but nothing works…

Thanks in advance