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TIC10024-Q1: Input interface for 48V system

Lorenz Hopfmüller
Prodigy 40 points
Part Number: TIC10024-Q1
Other Parts Discussed in Thread: TIC12400, , TIC12400-Q1

Dear forum,

we're planning to use the TIC10024-Q1, TIC12400, TIC12400-Q1 in a 48V system, with Vbat,max=56V.

The IC is supplied from a regulated 12V.

All inputs are switches towards GND.

We have two requirements for the device input:

  • Input is safe for an extended shortcut to battery voltage of 56V, also when regulated 12V is off
  • able to detect an external shortcut to high or to a neighboring input through a manipulation of wetting currents and input probing.

Would below network be sufficient to achieve this? Left side is external connector side, right side goes towards TIC12400 pins, two channels are shown.

Idea behind this is: The resistor divider network scales the max 56V down to 28V to stay in the safe 40V range of the TIC12400.

The diode provides a low-impedance path for the wetting current for a closed switch.

This network would still allow us to detect an external harness shortcut to 12V or Vbat by setting the wetting current to 0mA and probing the input then. A neighboring shortcut we would detect by setting the neighboring input's wetting current to a high value and probing then.

Happy to hear any additional ideas (or devices) that could help achieve that behavior.

Best regards,

Lorenz

  • +1
    TI__Mastermind 33360 points

    Hi Lorenz,

    This sounds like an interesting idea and one that looks like it should work.  The ESD cells in the TIC10024 and TIC12400 devices will turn on at approximately 40V and provide a low impedance path to GND.  If the voltage on the input pins rises above 40V, then you could have a large current flow through the INx pin.  Your clamping diode and resistor divider network should limit the voltage on the INx pin and prevent this situation.  The bypass diodes also look like they should provide a suitable path for the wetting current around the resistor divider and you have thought through this pretty well.

    The only thought or suggestion I have would be that if you found a suitable clamping diode for your application that could clamp the input pin voltages at a level less than 40V, then you could eliminate the resistor divider network and bypass diodes for the wetting current.  Either approach should work and the key concern is to make sure the voltage stays less than 40V to prevent the device's ESD cells from turning on.

    Yes you can use the device configurations for diagnostic testing and detection of shorts.

    For diagnostic testing and short detection (either to Vbat, GND, or a neighboring input channel) I would recommend the TIC12400 or TIC12400-Q1 for the ADC sampling option.  This will allow more accurate measurements compared to the comparator option.  For example an open switch or a short to Vbat would both be above the comparator threshold and be difficult to determine whether it is a short or a normally open switch.  The ADC would be able to tell you whether the voltage is higher than normal due to a short as compared to an open switch.

    For neighboring pin diagnostic testing, you will need to use the continuous current mode, and not the polling mode, to ensure the wetting current from a neighboring input channel is active while polling the various input pins and checking for shorts.  This concept is similar to how the device can be configured for Matrix Polling.

    Regards,

    Jonathan

  • 0 in reply to Jonathan Nerger
    Prodigy 40 points

    Dear Jonathan,

    thanks for the quick and helpful response - good to know we're on the right track here.

    Clamping the input voltage at the connector pin to <40V is hard to achieve - the Vbat power levels are high. So, either very significant power would have to be dissipated, or a series resistor at the input pin would cause significant voltage drop for the wetting currents. Hence the approach of not dissipating the excess voltage, but scaling it down to safe levels.

    Thanks also for your recommendations regarding diagnostic testing and short detection.

    We'd be interested in a future device similar to the TIC10024/TIC12400 that can handle >48V at the inputs - I'd expect that's relevant for a lot of 48V applications.

    Best regards,

    Lorenz