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LMV761: Phase Reversal at input common mode exceedance

Christoph Hofer
Prodigy 10 points
Part Number: LMV761
Other Parts Discussed in Thread: TLV3201

Tool/software:

Hello,

I would like to know if it can be guaranteed, that the LMV761 (LMV761MFX/NOPB to be concrete) does not go into phase reversal if one of the inputs exceeds the common mode input voltage range, while still being inside the maximum input voltage range? In my application the other input would always be within the input common mode range.

For instance:
The amplifier is supplied with 3.3V, hence an input common mode voltage range according to the datasheet of 2.0V.

One input is fed by a ramp signal ranging from 0V to the supply voltage, while the other is at a steady voltage below 2.0V.

The comparator output is expected to trip when the voltage of the ramp signal exceeds the voltage of the steady voltage. What happens when the ramp signal goes above the CMVR of 2.0V? Does the output remain stable or may there be a inverted phase at the output?

Unlike the TLV3201, which specifies NO phase reversal even if the inputs go beyond the supply voltage, the LMV761 does not specify anything. 

  • 0
    Guru 286790 points

    Assuming that the LMV761's inputs are the gates of P-channel MOSFETs, one input going to VCC cuts off the transistor harder than normally, which results in the correct output. In that situation, the electrical characteristics, especially the propagation delay, are no longer guaranteed.

    (In general, phase reversal happens only when both inputs are invalid, or if one input goes beyond the supplies.)

  • 0 in reply to Clemens Ladisch
    TI__Guru**** 153886 points

    See Clemens comments. It is expected to work however data sheet does not specifically say that it will work. Use a rail to rail input comparator to eliminate this  risk.