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TPIC1021

Ian Benton
Prodigy 210 points
Other Parts Discussed in Thread: TPIC1021

I was using TPIC1021 in receive mode, and getting lots of data corruption.

To investigate I looked at the bus signal and the RXD signal on the scope and saw nothing unusual  - nice slew-rate limited signal with no ringing on the bus, nice square edges on RXD.

I moved the connection from the UART to a capture input of my MCU, and found lots of pulses at 10µs intervals, whereas they should be 104µs for the 9600 baud test signal I was using.

I removed the TPIC1021 and replaced it with two resistors (27k. 10k) to divide the bus voltage from 12V to 3.3V, and it now works perfectly.

I can only think that the TPIC1021 is taking some power supply noise and amplifying it to make valid signals that are too short to see on a 20MHz digital scope.

Any thoughts/suggestions?

If not, I'll stick with the two resistor design - cheaper than a TPIC1021!

  • 0
    TI__Guru 59540 points
    Hello Ian,

    As your question centers around the TPIC1021, I will move your post to the automotive forum so that the experts with this device can offer their assistance.
  • 0
    Guru 10570 points
    What have you checked?

    Have you followed the decoupling recommendations?

    Robert
  • 0 in reply to Robert Adsett72
    Prodigy 210 points

    There is 1µF 1206 ceramic between V+ and ground within 6mm from the IC.

    There is 3.3k in series with a diode pull-up on LIN.

    There is 10k pull-up to 3.3V on RXD.

    EN goes to +3.3V

    Other pins are left disconnected (including TXD which is relying on its internal pull-down) - was that unwise?

    I checked LIN and RXD waveforms on a scope (Tektronix TBS1022, 20MHz digital), and both look clean - no ringing, no spuriae.

    The MPU is a NXP LPC1315 clocked at 72MHz, so it can obviously see shorter pulses than my scope can see.

    Connecting RXD to a capture input suggests that the pulses may be about 10µs apart, and the PSU runs at 100kHz - so I can guess the origin of the noise, but can't see it.

  • 0 in reply to Ian Benton
    TI__Mastermind 23810 points
    Ian,

    Sorry to keep moving this around, but the engineers monitoring the industrial interface forum typically cover this device.

    -Clancy
  • 0 in reply to Ian Benton
    TI__Intellectual 2855 points

    Hi Ian,

    Can you provide some more information on the application and also share schematics around LIN part?

    while monitoring the bus/RXD what was the sampling rate set on the scope, can you try monitoring the wavefrom with maximum sampling rate possible on scope to understand better.

    Regards

    Tejas

  • 0 in reply to Ian Benton
    Guru 10570 points
    Personally, I wouldn't trust internal pull downs but I suspect that's not your issue. The 72MHz is less significant than the 9600 baud. Your scope should be more than fast enough.

    Robert