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TPIC6B595: Upgrading from TPIC6595

John Capesius
Prodigy 10 points
Part Number: TPIC6B595
Other Parts Discussed in Thread: TPIC6596

I have been using the TPIC6595N in an outdoor LED Sign application for 19 years and it has worked great.  Because of lack of inventory I upgraded to the TPIC6B595N because it looked like a higher power version of the TPIC6595N.  The first ones I tested worked great but now that I've put them in a 12 digit sign(1 per digit) it has been very inconsistent.  The 7 segments digits are flickering on and off randomly except the first digit controlled by the micro directly.  This is with the original code and a modified one that is slowed down.  There is .1uf decoupling cap at each IC.  Any ideas what would be the difference and is there anything I can try?  I have noticed it gets better with a scope probe attached so thought maybe some capacitance might help. Let me know any other info you need from me. 

Additionally, I had 2 TPIC6595Ns in stock still so I replaced the 1st and 5th TPIC6B595 and the sign seems to operating better with just an occasional flicker of a segment that isn't supposed to be on.  

Thanks   

John 

  • 0
    TI__Genius 12915 points

    Hi John,

    Firstly I want to confirm that the flicker happened during data transmission, when stopping sending data, the outputs should be stable right?

    I suspect the drive capability of TPIC6B595N SER OUT is not as strong as TPIC6595N. The data shifted out form the 1st TPIC6B595 may be distorted to the 2nd one. Could you help to capture the waveform of SER IN / SRCK / RCK / DRAINx current, with the flicker channel?

  • 0 in reply to Hardy Wu
    Prodigy 10 points

    Hardy,

    Thank you for looking into this and the reply.  It was an issue with the SER OUT being synched with SRCK causing issues when I added more in series.  There is a slight difference in timing requirements with the TPIC6B595 which I hadn't thought would be an issue.  I ended up switching to the TPIC6596 series which latches the SEROUT to the falling edge of the SRCK and this fixed my issue. 

    Regards,

    John