TLC5940 with only 3 micro pins?

Hello Logan,

To be honest, I never tested it, but I do not think so. You need SIN and SCLK for data to be clocked into the IC. You need GSCLK to turn on and off the outputs and you need XLAT to latch the new data into the GS registers. In addition, I do not think that this will work without having the BLANK signal.

Maybe you will be able to find a part in our LED driver portfolio which still matches your requirements and has another interface. We have 2 16 channel drivers that are using I2C, for example. Please have a look onto the LED drivers web page

http://focus.ti.com/paramsearch/docs/parametricsearch.tsp?family=analog&familyId=480&uiTemplateId=NODE_STRY_PGE_T,

Best regards,
Brigitte

Hi Brigitte

I already have it wired up to 4 micro pins as follows

Micro connected to SIN, SCLK, XLAT and GSCLK.

BLANK wired low.  VPRG wired low. DCPRG wired  high. IREF wired though 7.812k to ground.

My GSCLK runs at 32khz.

I initialize by shifting 193 bits in to overflow the input shift register and then latching as 

described on page 17..

Then I shift in 192 GS bits every 125 ms to set the GS.

But so far, no led output?  Should this work?

Thanks for the LED driver web page link.  It looks like the TLC9571 is just what I need 

since it has 16 bit GS, more than enough output channels, and only 2 micro pins required.

However, it is a new part that is not stocked anywhere.  If I put this in my new design, 

how long before I can get parts from distributors?

Thanks,

Logan 

Hello Logan,

In the datasheet on page 19 you can find a description of the grayscale PWM operation. The following sentence is the first one: "The grayscale PWM cycle starts with the falling edge of BLANK." A falling edge on BLANK starts the GS cycle, therefore you should not pull BLANK completely to GND. This means you need another output of the microcontroller, sorry.

Please ask your distributor about the time when you can get TLC5971.

Best regards,
Brigitte

Hi Brigitte

Can I connect the VPRG and BLANK pins and drive them from 1 of my micro pins?

I would like to use DC but I am low on micro pins.

Logan