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Original question:

PGA281: Controlling overshoot?

PGA281: Absolute maximum short term input terminal input current

Chris hl93
Prodigy 160 points

Part Number: PGA281

Hello,

I see on DS page 2 that short term fault current into the "terminals" must be limited to +/- 10 mA with external current limiting to prevent permanent damage to the part.  With the PGA281 supplied by +/- 15V rails and a 3.2K resistor in series with each of the terminals, I measure 10.0V across each resistor (1.62 mA) when I apply +25.69V to the input side of each of the resistors, therefore, there is a total of 6.2 mA of fault current flowing to the 15V VSP pin of the part, but only 3.1 mA into each input pin.

Does this absolute maximum spec on the datasheet imply that 10 mA can be flowing into each input pin or is it implying that a total of 10 mA can be flowing into the input pins?

Thanks,

Chris

  • 0
    TI__Guru 55466 points

    HI Chris,

    The internal ESD structures of the device are primarily intended to protect for short duration ESD events.  Each pin has an independent ESD cell, and the input diode clamps can withstand +/-10mA each, however, exposure to this fault for extended periods of time may degrade device reliability. 

    The inputs are diode clamped to the supply rails, therefore, I recommend adding transient-voltage-suppression (TVS)  diodes at the VSP/VSN supplies that turn on slightly above +/-15V to limit the maximum voltage seen by the supply pins of the PGA281 that will prevent the supply exceeding the maximum VSN to VSP rating on a fault condition.

     In the case of having the VSP/VSN supplies on, and the inputs are exposed to +25.62V, the 3.2-kOhm resistors will see approximately 10-V across them, and the current per input pin should be approximately 3.1mA.  However, if there is any possibility that the device may be exposed to +25.69-V at the inputs; while the VSP/VSN supplies are off on a fault, the 3.2-kOhm input resistors will limit the current to ~8mA per input, getting close to the max ratings. If there is a possibility of the device to be exposed to this condition, or these conditions may occur often or for extended periods of time, I recommend to increase the series resistors to ~10kOhm to reduce the input clamp current further.

    If the device is expected to be exposed to fault conditions for extended periods of time, it is always good idea to  increase the value of the input series resistors.  Adding TVS protection diodes at the supply pins is always recommended.

    Thank you and Regards,

    Luis    

  • 0 in reply to Luis Chioye
    Prodigy 160 points

    Understood - thank you!

    Chris