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TLC5955: power up issue

Aivaras Sakauskas
Intellectual 1600 points
Part Number: TLC5955


Hi,

  • At power up, the LEDs do not always come on.  Any one of the 5 chips may fail.  However the data still passes through the failed device so we see data coming out of the SOUT pin.  So, it we have 2 chips daisy-chained, the first device can fail but the second device can still power up correctly.
  • When a chip has failed, we cannot recover it except by power cycling the devices.
  • The failure does seem to depend on the power supply voltage but we cannot find a voltage which is consistently reliable.
  • When the system powers up correctly, it appears to work correctly thereafter.  We have only tested this in a diagnostic mode however which may not exercise all the register settings.
  • We are running the GSCLK at 32MHz which is close to the spec limit of 33MHz
  • The GSCLK is running asynchronously from a Xtal oscillator so has no relationship to SIN, SCLK and LAT (see attached picture).
  • The LED outputs are connected to 16 RGB LEDs to a positive power supply so all 48 outputs are used.

 

1.Can you check with your design team please that it is OK to run GSCLK asynchronously, or not? 

2.Are there any other possible reasons that the device may latch up in a state with all the LEDs off?  

  • 0
    TI__Expert 3190 points

    Hi Sakauskas,

    It is OK to run GCLK asyncchronously.

    For you case, please help to check the below items,

    1. what is the current limit value of the supply power?  the reason of the power-on issue may be lack of capability of power supply

    2. Check the digital sequence, you can share the signals/ programming codes/ waveform of SIN/SCLK/LAT, so we can check if the logic is right

    3. 769bits FC data, is the configuration right?

    Let me know the result of the former three items.

    Regards,

    Shawn.

  • 0 in reply to Shawn Ding
    TI__Intellectual 1600 points

    Hi,

    Is the GSCLK recommended to be asynch or should be avoided?

    My concern is the on the diagram below (page 14) it appears the GSCLK is not a continuous clock and all related to the LAT signal which means its synced. Am I wrong?

     

     

    We are violating some condition at start up which prevents the TLC5955 working reliably. If its starts correctly it will work correctly for the duration of the run until power down.

     

    1. We believe we have sufficient current

    2. Please see my comments above

    3. We believe that’s correct

  • 0 in reply to Aivaras Sakauskas
    TI__Expert 3190 points

    It depends on the configuration of Bit 368, bit 367, bit 366. If Bit368=bit366=1b, there is no need to set LAT signal.