• State
  • Locked Locked
  • Replies 1 reply
  • Subscribers 63 subscribers
  • Views 243 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TLC5941 dimming using the DOT correction

Jamaal_Charles
Genius 3245 points

Hello,

We have a mode where we have to dim to really low levels.  Is there a trick to doing this?  We been able to use the grey scale for brightness and on/off without any trouble, and have just left the DOT register at 1's.

Our assumption has been the DOT correction is supposed to be 6 bits/LED, or 96 bits for each device.   We've played with sending various combinations/patterns to the DC mode register, but we are struggling to see any correlation between the values we send and the results we see in terms of brightness.  The brightness does change, but we just can't predict what values/patterns we should be sending.  We've even tried sending values in other bit alignments, from 2 bits, to 16 bits per value, and every size in between. Again, just can't figure out what works. 

Also, the datasheet says that "the TEST pin must be connected to VCC to ensure proper operation of the DOTcorrection circuitry".  We  are doing that.  The only other thing to note is that we aren't conecting a couple of the LED outputs. I wouldn't expect that to be an issue, but if that would cause some sort of error state, I wanted to mention that.

Any thoughts?

Thanks 

  • 0
    TI__Genius 14317 points

    Hi JC,

    It sounds like you are able to succesfully write to the Input Shift Register and the 6 bit DC register for each channel (Mode set to Vcc). The "Setting Dot Correction" section on page 17 of the Data Sheet describes how the serial data should be input starting with channel 15 MSB (MSB first) to chanel 15 LSB followed by channel 14 MSB to LSB and so on to channel 0 MSB to LSB for a total of 96 bits. XLAT controls write and hold of the DC register data as described on page 17. I've attached an App. Note that also describes the data sequence and may help out. Fig 11 in the Data Sheet on page 12 shows how the output current for each channel varies with each DC 6 bit value (0 to 64 decimal). The DC value varies the current from 0 to 100 % of Imax as set by Riref. If you want 6 bit control in very small current steps, you'll have to set Imax lower. Imax can be set in the range 5 mA to 80 mA.

    slva267a.pdf