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TLE2144: TLE2144 driving inputs when no supply voltage is applied

high speed guy
Expert 3175 points
Part Number: TLE2144

Hi,

Can you tell me the impact of driving the inputs of this device when no supply voltage is applied.   Our situation is that until we power up this portion of our board these inputs can be driven by +/- 15V with current limiting by a 10KΩ resistor in series.  Is this an acceptable approach?  What will be the impact?   Can the inputs of this device handle this situation with the current limiting implemented with the resistor?

Thanks,

HSG 

         

  • 0
    TI__Guru 63000 points

    I presume that by "no supply voltage applied" you mean the supplies are floating (high impedance) and are not grounded (0V supply voltage).  If so, as long as the differential input voltage is less than +/-20V, and you have 10k resistor in series with each input terminal, no damage will occur regardless of the Vcm (see below max input current of +/-1mA).

  • 0
    TI__Guru* 93105 points

    Hello HSG,

    We don't characterize the behavior of our Precision Amplifier Op amps unpowered so there are no assurances inferred by the datasheet regarding the TLE2144 when in such a state.

    I just made some quick bench checks and each input appears to have one ESD diode to Vcc- and possibly two series diodes to Vcc+. If the supply pins are not powered and we presume they are floating at a high impedance, then when either +15 V, or -15 V, is applied to an input one or the other ESD diode paths will be forward biased. 

    Since the forward biased diode leads to either the Vcc+, or Vcc- pins current from the diode will be directed into one of those supply pins. Because only one of the supply pins is being supplied current, the Op amp will not be normally powered. That might result in a latch condition when the Op amp becomes powered up, or it may not. However, including a series resistance with the inputs such as 10 kilohms very much limits the current that can flow from an input to a supply pin.

    Realistically, due to the 10 kilohm series resistance, ESD diode forward voltage and whatever the TLE2144 circuits might draw, the current would likely be less than a milliampere. Latches usually require high current to form so it is unlikely to happen with the high series resistance in the circuit. I expect the TLE2144 will be able to tolerate the unpowered input voltage condition, without degradation providing the 10 kilohms resistors are added to the inputs.

    Regards, Thomas

    Precision Amplifiers Applications Engineering