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Low SN65HVD08D drive capability when powered from 3.3V

Paul Eccles
Prodigy 100 points
Other Parts Discussed in Thread: SN65HVD08

The SN65HVD08D appears to be unable to drive 1.5V differential output into a 54R load when powered from 3.3V. I've tested this with a 55R load, and only get a swing of 1.2V. When I remove the the SN65HVD08D and load a SN65HVD12D into the same circuit (also powered from 3.3V), then the SN65HVD12D doesn't have this problem and can drive a healthy 1.8V into the same load.  I've tested this with several parts that weren't from the same batch. The ICs' case markings appear to be correct.

Below is a table of some DC differential output voltage measurements I made with a SN65HVD08D driving various loads (resistors wired between the A and B terminals).  The part was powered from 3.3V and both the DI and DE pins tied to the same 3.3V rail.

Is anyone able to repeat my measurements?

Open circuit 2.58
22k 2.41
10k 2.25
2.2k 1.97
220 1.67
110 1.47
55 1.18
  • 0
    TI__Mastermind 28265 points

    Paul,

    we're looking into this.

    regards, Thomas

  • 0 in reply to Thomas Kugelstadt
    Prodigy 100 points

    Thanks for this Thomas. I raised this TI Asia Tech Support in March and they did get back to me, however subsequent emails were unanswered. My contact did say he was ill so perhaps this explains the silence.

  • 0 in reply to Paul Eccles
    TI__Mastermind 28265 points

    Paul,

    fortunately for us the taken load characteristics (see below) for the HVD08 does not confirm your measurements. The HVD08 provides a solid 1.7V at 54 ohm differential load.

    I have been informed that the HVD08 and the HVD12 in fact have the identical output stage. Also we confirmed a similar question through a scope shot back in March. If you search the forum for SN65HVD08 you should a query for March. In the response chain to our Asian support you will find the scopw shot.

    Regards, Thomas

  • 0 in reply to Thomas Kugelstadt
    Prodigy 100 points

     

    Hello Thomas, thanks for the very speedy response. I very much hope that what you're saying is correct: we have a lot of these in the field and a healthy output swing is necessary for this project. Yes, I'm guessing that March question was mine, as I suggested in my previous reply. I performed the forum search you recommended but couldn't find the thread ... I'm new to this forum so perhaps I'm doing it wrong.

    The problem I have is that I've repeated the measurement on several boards that were manufactured over an ~8 year period. This is why I don't believe the problem is limited to a single batch. Also, I've performed the check on units fresh out of the tube from Digi-Key, so I don't suspect damage or counterfeit parts. My customer has repeated the measurements on different units and confirmed the same thing, which suggests I'm not going mad.  The fact that I can drop in a HVD12D and the low output differential isn't seen suggested to me that our circuit isn't to blame. This is why I've raised this here.

    I'll dig up a couple a fresh units and repeat my tests. With any luck I’ve gone wrong somewhere. I’ll let you know.

  • 0 in reply to Paul Eccles
    TI__Mastermind 28265 points

    Paul,

    please send me you email address. I need to send you some Failure Analysis documents which you want to fill out and send back with minimum 2 samples.

    This is the fastest way to verify measurments.

    My direct email address is tk@ti.com

    Thanks, Thomas