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DAC8750: DAC8750 TVS Selection

user4499359
Intellectual 450 points
Part Number: DAC8750

Is TVS Selecting CD143-SR70 Right?

  • 0
    TI__Expert 5820 points

    Hi,

    Yes, this is typically what we recommend for clamping diodes and is the device included on our DACx760 EMC-EVM. You can find additional details about EMC protection on the EMC enhanced TI design guide: https://www.ti.com/lit/ug/tidu011/tidu011.pdf .

    Thanks,

    Garrett

  • 0 in reply to Garrett Satterfield
    Intellectual 450 points
    Dear team:
    Due to lack of experience, it can help to select two clamped diodes and “unidirectional TVS Diode Pari” under asymmetrical 24V power supply. The purpose of the circuit is 4-20mA output.
  • 0 in reply to user4499359
    Intellectual 450 points
    Due to 24V asymmetric power supply, I chose 2 SMAJ24. Working voltage 24V, breakdown voltage 26.7-29.5V.
  • 0 in reply to user4499359
    Intellectual 450 points
    "unidirectional TVS Diode Pair", I chose CDSOD323-T24SC.
    There is also a problem that is not understood. There are two levels of TVS protection on the circuit, separated by a 15 ohm resistor. Is it enough to protect one level?
  • 0 in reply to user4499359
    TI__Expert 5820 points

    Hi,

    The selected TVS diode should provide minimal leakage at normal operating voltages and break down shortly after this voltage is exceeded. The maximum normal operating voltage at IOUT will depend on the load you are driving with AVDD being the maximum possible voltage. A load of about 1.2kOhm including cable resistance driven at 20mA would result in a voltage of 24V.

    If you chose a working voltage of 24V the leakage at 24V will be about 1uA. This leakage will result in loop current error.

    In DACx760 EMC-EVM, which I linked in a previous post, 15V working voltage TVS diodes were used as the maximum expected voltage at IOUT is around 12V. This ensures that the leakage at this maximum voltage will be much less than 1uA. The resistor that you mention is to limit the current to less than 10mA at the breakdown voltage of the TVS.

    I am unclear about what you mean by 'asymmetrical 24V power supply'. The DACx750 only has a positive power supply, AVDD. Can you clarify this?

    Thanks,

    Garrett