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TLV3011 Input Voltage Range

Gary Whelan
Prodigy 60 points
Other Parts Discussed in Thread: TLV3011

Originally mistakenly posted under Audio Amplifier forum.  Moved to /etc... Amplifiers & Other Linear

If one of the TLV3011 inputs (the inverting for example) is driven to a voltage high or low enough such that the diode to the associated supply rail conducts, will the output still be as expected?  Or can the output phase reverse?  Let's say there is a 10kOhm resistor to limit the current.

 

  • 0
    TI__Guru* 93105 points

    Hi Gary,

    The TLV3011 input ESD cells do not have an internal connection to positive rail. This normally off cell is activated by a fast,  positive-going ESD event. It turns on quickly and clamps the ESD voltage to a low value protecting the comparator input circuitry. The same cell becomes a simple diode to a negative going ESD voltage and clamps at the forward bias diode voltage.

    It is important that the inputs not be driven beyond the absolute maximum ratings of -0.5 V to (V+)+ 0.5 V. If the input is kept within that range the output should not invert.  Any resistance added in series with the input will help limit the current should the input be over driven.

    Regards, Thomas

    PA - Linear Applications Engineering

  • 0 in reply to Thomas Kuehl
    Prodigy 60 points

    Hello Thomas,

    The TLV3011 data sheet states the following:

    >> (2) Input terminals are diode-clamped to the power-supply rails. Input signals that can swing more than 0.5V beyond the supply rails should be current limited to 10mA or less.

    Is this just a over simplification of the input circuit for the data sheet? 

    If the inverting input is driven beyond (V+)+0.5V will the output invert?  Please see attached oscilloscope plot.

    The orange trace is the input to the circuit.  The blue trace is the inverting input of the TLV3011.  (Note, there is a 10kOhm resistor between the input of the circuit and the input of the comparator.)  The green trace is the output of the comparator.  V+ = 3.3V.

    My concern is the output might invert; it did not on this example, but this is just one part.

  • 0 in reply to Gary Whelan
    TI__Guru* 93105 points

    Hi Gary,

    I just set up a TLV3011 in the lab and tested it with the inverting input being over-driven by as much as 0.5 V beyond the supply rails, the input signal absolute maximum. The comparator output did not invert and did not show any tendency to do so. Most modern operational amplifier and comparators are designed not to invert when over-driven and that is the expected behavior of the products today.

    Also, when I mentioned that the TLV3011 doesn't have an ESD steering diode to the positive supply rail I was basing that on the internal schematic diagram. While in the lab I checked for a diode between the inputs and the negative and positive supply rails. Indeed the negative diode checks from a simple ohmmeter test and also a DMM diode check. The input to the positive rail showed a multi-Megohm resistance, but not a diode-like characteristic. The diode check produced a voltage unlike the typical 0.65 V level seen for a diode. It probably was a leakage resistance path being developed within the unpowered device. Therefore, all indications are there isn't a diode between the input and positive supply rail.

    I suspect the Vcc + 0.5 V limit was set to assure that the CMOS input stage is protected from over-voltage and also prevents the normally off ESD cell from being triggered on.

    I hope this helps answers your questions.

    Regards, Thomas

    PA - Linear Applications Engineering

     

  • 0 in reply to Thomas Kuehl
    Prodigy 60 points

    Good Morning Thomas,

    Thank you for checking this out for me!

    Just out of curiousity, what does one look for the verify "did not show any tendency to do so", refering to output inverting?

    Best Regards,

    Gary

  • 0 in reply to Gary Whelan
    TI__Guru* 93105 points

    Hi Gary,

    It may have been better if I had just left my response to the TLV3011 did not output invert. Some older operational amplifiers that I have evaluated on the bench, that do exhibit output inversion, will show a small amount of reversal or fold back as opposed to full output reversal. This doesn't happen within the specified input CMV range. But beyond that input range the amount of fold-back increases until complete reversal is observed. I am certain that was what I was in the back of my mind when I mentioned the TLV3011 "did not show any tendency to do so."

    Regards, Thomas

    PA - Linear Applications Engineering