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TSC888 failure modes

Discussion in 'Electronic Design' started by Aung Ko Ko Thet, May 28, 2013.

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  1. Hi All,

    Is there any one who has good experience in using high side current sensors in bi directional DC Motor Controls?

    We are using TSC888 high side current sensors on the 12V DC Supply lines to 7 DC Motors, 4 bidirectional and 3 unidirectional. We use L293 ICs as motor drives.

    There has been sensor failures within two weeks of running the system continuously. (Approximately 80 hours). The sensors always fail in such a way that the output shows 10 times the actual value.

    I would like to know possible root causes for this from any one who has experience in using TSC888 in the motor controllers.

    Thanks in advance
    Aung
     
  2. John S

    John S Guest

    Probably due to over-voltage. We had a similar failure using a TS1100.

    John
     
  3. Jamie

    Jamie Guest

    We out actually seeing some circuitry, it would be hard to say but I
    am leaning towards underrated parts or, EMF noise that results in HV is
    getting back to the sensor circuit via the motors.

    But my guess would be that a shunt resistor is opening,

    Jamie
     
  4. John S

    John S Guest

    Our shunt resistor value is .004 ohms. It is less than a zero ohm
    substitution part in most cases. The Kelvin connections are now as good
    as they can get on this second board layout and there have been no failures.

    Note that the common-mode specifications are very important here.

    Are there any spikes on the line that will exceed the common-mode specs
    of the chip? My bet is a huge YES!

    So, I don't think you have used these parts nor have you studied the
    specifications in detail.
     
  5. Hi John,

    Thank you so much for your kind interest and comments on this matter.

    We have found two things:

    1. We have carried out validation measurements to make sure that nothing would exceed the absolute maximum ratings. Only one problem, there is a negative going ring 20 us perioud (4V pk-pk) for 60 us when the system is power cycled. It is due to the low quality 12V Switch Mode Power Supply. The rating of the IC says the common mode minimum is -0.3V. The negative going peak of -2V is already exceeding. So we have a preliminary conclusion that this could be one of the root causes of IC failure.

    2. The ESD spec: of the IC is quite low, HBM 1kV and MM 100V. So it is moresensitive to ESD than other ICs, as we the system is open and the PCB is exposed to human interactions for this moment in time, it has a high ESD risk.

    Please let me know your opinion also

    Regards
    Aung
     
  6. Hi Jamie,

    Thanks for your kind comment.
    Actually, there has been no failure in the shunt resistor. After replacing the IC, the current measurement systems works fine. It is basically due to the IC which somehow malfunctioned.

    Regards
    Aung
     
  7. Jamie

    Jamie Guest

    You need to do a couple of things.

    1.
    You need to provide a clamp diode on the supply line to grab
    any below ground problems. This is a common issue with flaky supplies
    and people connecting things backwards. A high current schottkey should
    work for that. One of my cases, I had to use an active clamp to suppress
    high currents due to ground faults from other equipment.

    2.
    The current sensor you are using has a diff voltage of 2 volts and if
    for some reason you get a high current pulse, which does happen for
    brief moments, you can exceed this. In cases like this, it is more than
    likely the front end does have diodes internally however, I didn't see
    if the unit actually has sinking resistors inside? So maybe some extract
    protection is in order, like R's of your own connecting the inputs to
    the shunts? Or, two diodes over the shunt to prevent the raise of
    differential voltage.

    3.
    You may want a big fat suppresser on your DC buss. The drive IC's you
    are using more than likely have diodes in the bridge to capture the
    regen energy and the motor could get into a free spin condition there by
    generating more energy back to the supply. When people are involved it
    is easy to get a motor load to be free spun out of control! (load swing)

    So going back to (1. issue), a high wattage zener of 12 volts is in
    order or active clamp (dynamic Brake R circuit), like I use..


    Jamie
     
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