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Power up issues with the TLC5916

Joseph Mibelli
Prodigy 80 points
Other Parts Discussed in Thread: TLC5916

I have a circuit with four TLC5916 driving numeric readouts, commanded by a microprocessor (SPI)

There are two separate 5V supplies, one that powers the processor and the drivers and one that powers the numeric LEDs.

Sporadically, some of the readouts fail to turn on. Recycling the power sometimes corrects the problem.

Is there a specific power sequence that needs to be observed in this case?

  • 0
    TI__Genius 14890 points

    Joseph,

    There are no power sequences that I am aware of.  Can you tell me what numeric LEDs you are using? 

    Does this happen on all devices?  I tested a single unit today without any issues.  How often does the system fail?  When you recycle the power, is it the driver power or the LED power?

    Regards,

    Dick

  • 0 in reply to Dick Stacey
    Prodigy 80 points

    Dick,

    I get mixed results with the power cycling.

    The basic issue is that the circuit functioned flawlessly with the Allegro A6275 and started to fail upon using the TI TLC5916.

    Is it a totally different device? Are there timing issues that I need to be aware of?

    I drive the devices from a microprocessor using a simple SPI configuration and there is no programming of internal functions. OE is permanently tied to ground.

    Thank you for your support.

  • 0 in reply to Joseph Mibelli
    TI__Genius 14890 points

    Joseph,

    I have reviewed the datasheet for the A6275.  There are a couple of differences that I see of note.  The A6275 has an under-voltage lockout mechanism and the TLC5916 does not.  This may have an impact on the power cycling.  The TLC5916 has a Special Mode allowing the user to set a gain register (for global dimming) and to read back any error conditions.

    For timing, it seems that the TLC5916 is faster so the timing set for the A6275 should work.

    Is the error you get only if the numeric LEDs are powered first?

    Regards,

    Dick

  • 0 in reply to Dick Stacey
    Prodigy 80 points

    Dick,

    I have located more of the A6275 and the circuit works flawlessly. I will be replacing all of the installed TLC5916 (for now).

    The failure mode is strictly that they fail to start-up (come up blank). If they do start-up (zeroes) they they accept the SPI information. But I have seen them drop out, at least once or twice.

    What can affect their start-up performance?

    Thanks

  • 0 in reply to Joseph Mibelli
    TI__Genius 14890 points

    Joseph,

    Would you be able to send the schematic?  Perhaps offline directly to me?

    Regards,

    Dick

  • 0 in reply to Dick Stacey
    Prodigy 80 points

    Dick,

    The problem is now resolved.

    The original firmware provided a negative going latching pulse as opposed to a positive one. A newly tested firmware, with the correctly shaped latching pulse works properly.

    I apologize for the confusing information.

    Thanks

  • 0 in reply to Joseph Mibelli
    TI__Genius 14890 points

    Joseph,

    Thank you for posting the resolution.  This may help us in the future for other people having issues.

    Glad you have it resolved and working well.

    Regards,

    Dick