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OPA2192: Fault Coverage

Mitchell
Expert 4915 points

Part Number: OPA2192

Hi Team,

My customer has a question on the OPA2192.

In regards to potential fault coverage, the sense buffer of their control loop may inadvertently be shorted to GND. If this occurs a large current spike may be seen at the input to the OPAx192 device. 

While the data sheet states protection to absolute maximum of +/-10mA, they are wondering about the equivalent specification with respect to energy. In this case they calculate about 500ns*25mA*100V = 250pJ. Would this low level of energy be enough to be concerned about violating the absolute max rating of the amplifier? Seems small enough?

RMS current over this span is on the order of 7.1mA.

Thanks,
Mitchell

  • +1
    TI__Guru* 93105 points

    Hi Mitchell,

    Since we do not characterize the precision op amps such as the OPA2192 in terms of input energy tolerance we don't have any information to say whether 250 pJ is safe or not. The inputs clamping diodes which bear the brunt of the energy and power dissipation during an input ESD event are quite robust. The 10 mA maximum is a dc continuous current so the power dissipation is on the order of 7.5 mW. We know that is a very conservative rating, but keeps users out of trouble by not exceeding it.

    During an out-of-circuit ESD event which the diodes are designed for the current can be much, much higher than 10 mA for a very short time duration. Some years ago we were looking into what an ESD cell diode might endure during an HBM or CDM ESD event and attempted to model it. It was surprising how high the current could be and how high the forward voltage of the conducting ESD diode could become during and ESD event.

    We determined that the peak current during the 2 kV Human Body Model (HBM) event was about 1 Ampere, and the forward voltage rose to as much as 10 V due to a fairly high internal resistance. We didn't have an exact model for the ESD diode so for simulation purposes we used a parallel RC circuit to represent the forward biased diode.

    The voltage and current response curves over an approximate 500 ns time span roughly produced averages about 7.5 V forward voltage, and 750 mA, respectively. If we apply the formula you used for energy E = time x power:

    E = (500 ns) ( 7.5 V) (0.75 A) = 2.8 uJ

    Certainly, that is higher energy level than the 250 pJ in question.

    Since we don't provide any energy tolerance ratings for of our precision op amps inputs in the product datasheets we cannot make assurances that the OPA2192 will tolerate the 250 pJ energy level. However, based on my crude estimation of the ESD cell energy during an HBM ESD event it does appear that it should be able to withstand this level.

    Regards, Thomas

    Precision Amplifiers Applications