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Faulty Toneing on 1394b PHY

Bill Evans
Prodigy 40 points
Other Parts Discussed in Thread: TSB41BA3D

We just built 10 prototype boards with one TSB41BA3A on each board.  6 of the boards seem to work fine (both of the populated ports link to a FireSpy).  The other 4 boards all have a pecular waveform on the TX+ and TX- outputs of all three ports.  Unconnected ports of the working boards have a pulse 666 usec. wide with a  burst of 48 MHz.  These occur every 42 ms.  This is the normal 1394b connection tone.  The other 4 boards have an approximately 2 volt pulse, 666 usec wide every 42 ms.  There is no 48 MHz toning on this pulse.    I have verified the power supply voltage (correct voltage no noise), power up reset timing (200 ms for oscillator to stabalize), external oscillator etc (frequency, duty factor and amplitude okay).  I can't think of anything else to look at.  As soon as I can get some replacement parts I will replace the PHY chips, but in the meanwhile has anyone seen this kind problem?

  • 0
    Prodigy 40 points

    Update

    We replaced the PHY chip with one drawn from in-house stock (same lot code) on 2 of the non-functioning boards.  Now, one has a normal connection tone waveform at room temperature.  The other still has the pulse with no 48 MHz tone on the TX+ and TX- outputs.  We cooled the boards with the replaced chips to -40 C in a test chamber.  The normal toneing on the "good" board changed to the pulse described above.  The other board conitnued not to work.  As the temperature was ramped back up, the normal toneing waveform on the "good" board gradually came back.  We raised the temperature to +71 C.  The wavefrom on the "good" board reamied "good" and there was no change on the "bad" board at +71 C.

  • 0 in reply to Bill Evans
    Prodigy 40 points

    Update 2

    We found that the resistor between pins 22 and 23 that is supposed to be 6.34 K  +/-1% was actually around 220 Ohms!  We replaced the resistor on one board that was not working at room temperaturea and now we see normal toning on the TX+ and TX- outputs.  Now the question is:  Did we stress the parts by powering them up with such a low resistor value?  Said another way, which is the greater risk, removing an 80 pin TQFP or just changing the reisistors and hope for the best?  Any insight into the likelyhood of premature failure would be appreciated.

  • 0 in reply to Bill Evans
    TI__Genius 16430 points

    Bill,

    Sorry for the delay - and thanks for all the additional inputs as well!

    I have been bouncing this off various engineers on the team.  The consensus is that we do not believe that should have introduced any pre-mature failure mechanisms...

    BTW, I also wanted to let you know the TSB41BA3A is NOT recommended for new designs.  The TSB41BA3D is a drop-in replacement with errata items fixed.

     

  • 0 in reply to DHarmon
    Prodigy 40 points

    Thanks Dan.  We will be adding the TSB41BA3D to the parts list.

    Bill