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DAC161S997EVM: input TVS diode calculation

Will Wang47
Expert 7670 points
Part Number: DAC161S997EVM
Other Parts Discussed in Thread: TPS7B69, DAC161S997, TPS7A16

Hi team,

My customer is using DAC161S997 in their project. The max loop voltage is 36V. The system use TPS7B69, 40V/150mA to supply the whole system. Now they use the SM6T39CA as the TVS diode at the voltage input to suppress high voltage, and now they want to make sure if it's OK? They refers to TIDU385A.

Hope you could help check this problem.

Thanks & Best Regards,

Will

  • 0
    TI__Genius 11750 points

    Hi Will,

    The TIDU385A design specifies an input range of 10V to 33V DC.  The TVS selected shows a 33.3VWM value, with 69.7VC.  Typically, the highest operating voltage will determine, VWM, the working voltage of the TVS diode. This parameter is often identified as the rated working peak voltage for the TVS device in providing high impedance and low standby current during normal operation.  At a maximum 36V, the TVS will more than likely start to conduct current, which may be specified in its datasheet.  It's also important to note that this particular TVS has a VBR (Breakdown voltage) value of 37.1V.

    My suggestion is to use a TVS with a higher VWM.

    Best Regards,

    Matt

  • 0 in reply to Matthew Sauceda
    TI__Expert 7670 points

    Hi Matt,

    Thanks for your answer. And I have another question, as I describe above, the max input is 36V, and the LDO max input voltage is 40V, I want to know if it's OK for this kind of design. Can it handle a surge voltage? Or if I should choose a higher input voltage LDO for my customer, for example 60V?

    Hope you could answer my question.

    Thanks & Best regards,

    Will

  • 0 in reply to Will Wang47
    TI__Genius 11750 points
    Hi Will,

    According to the datasheet the TPS7A16 family has a wide input voltage range of 3V to 60V, so I'm not sure where the "40V" metric you provided above is coming from. You can use this information to select a TVS that has a clamp at ~60V and working voltage up to 36V. It may just come down to a simple trade-off of protection vs accuracy @ the max input voltage (36V).

    Best Regards,
    Matt