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INA236: Input common mode undershoot protection

Manuel Tosone
Prodigy 10 points

Part Number: INA236

Hello,

I would like to ask a question about the Absolute Maximum ratings of the INA236. Specifically the minumum input common - mode voltage on Vin- and Vin+ and the maximum input current into any pin.

Is it correct that the voltage on Vin- and Vin+ can get lower than -0.3 V if the input current is kept below 5 mA?

We use this part in a low side current sensing (see schematic below), where the voltage on the shunt resistor can experience negative undershoot when the load is diconnected. The undershoot is clamped to -1.5 V by D21 (TVS).

We calculated the value of R87 and R88 to be 260 Ohm to ensure the input current neve exceedes 5 mA.

In our testing we found that the error introduced by this high resistance is acceptable for the application.

Is this a valid way to protect the inputs of the IC?

 

Kind regards,
Manuel

  • +1
    TI__Expert 8250 points

    Manuel,

    Thanks for the question and using the E2E forum.

    For some reason your schematic image isn't loading on my end so I can't see it, but I'll answer based on your description.

    Yes, this is a valid protection strategy. Here is the technical rationale from application note SBOA615:
    • The −0.3 V minimum common-mode rating exists because the ESD cell's body diode becomes forward-biased when the input drops below approximately −0.3 V. This causes current to flow into the ESD clamp structure.
    • As long as this current is limited to less than 5 mA, the ESD cell can handle it without generating excessive heat or causing damage.
    • The datasheet and application note both explicitly confirm that input resistors limiting current to < 5 mA peak are an accepted technique for protecting against negative voltage excursions below the −0.3 V threshold.
    One thing to double-check: Your worst-case current calculation should account for the full voltage across the resistors. If VIN pins are near GND (0 V) and the TVS clamps to −1.5 V, the voltage across each resistor would be approximately 1.5 V. With 260 Ω:
    I = 1.5 V / 260 Ω ≈ 5.77 mA
    This slightly exceeds the 5 mA absolute maximum. You may want to consider increasing R87/R88 to at least 300 Ω (1.5 V / 300 Ω = 5.0 mA) or ideally higher (e.g., 330 Ω) to provide margin. In practice, the TVS clamping voltage at low currents may be lower than 1.5 V, but it is best practice to design with margin against the datasheet limit.
    Please let us know if you have any other questions.
    Louis
  • 0 in reply to Louis L
    Prodigy 10 points

    Hi Louis,

    Thanks for your reply!

    The information you shared about the INA236 input structure was very helpful.
    We are now confident that the component will work in our application.

    Kind regards,
    Manuel