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TLV7032: Clarification of Overdrive

Cameron Perl
Expert 5545 points
Part Number: TLV7032


Tool/software:

Hey team,

How does the overdrive feature of this amplifier work? Does it just allow the device to swing the input beyond the supply? What does this look like? PSpice model notes that if the supply goes beyond the recommended operating range the outputs will float to mid supply which I doubt is what the device does.

Use-case:

Vcc=3.3V

Vee=0V

Vin-= 2V constant reference

Vin+= Sine wave between -0.25V and +3.5V (source impedance of 6kOhm)

Are we currently violating the Vin spec by having Vin+ swing down to -0.25V?

Thanks,

Cam

  • 0
    TI__Guru 62536 points

    Hi Cam,

    No, the actual, physical device output will NOT revert to 1/2 supply. That is a feature of the SPICE model to alert the user that there is a violation (there is no universal way to pop-up an error message in SPICE models - so we made it do something "stupid" to catch attention).

    From section 6.4.1 of the datasheet:

    "The TLV703x and TLV704x input common-mode extends from VEE to 100mV above VCC. The differential input voltage (VID) can be any voltage within these limits. No phase inversion of the comparator output occurs when the input pins exceed VCC and VEE.

    The input of TLV703x and TLV704x is fault tolerant. It maintains the same high input impedance when VCC is unpowered or ramping up. The input can be safely driven up to the specified maximum voltage (7V) with VCC = 0V or any value up to the maximum specified. The VCC is isolated from the input such that it maintains its value even when a higher voltage is applied to the input."

    So you are technically violating the input range at both positive and negative edges by -125mV and +200mV. But the abs max is -0.3 to +7V, so you will not be causing any damage. But technically, we are saying that malfunctions could occur in the range between the specified (-0.1V) and abs max (-0.3V).

    Is it possible to slightly attenuate the input signal by 200mV or more?

    It is up to you if you wish to exceed the specified range. I don't think you will have any issued. If you do wish to exceed the specified range, I would recommend placing a resistor (1k) in series with the input to limit any fault current, particularly in the negative direction.

    If you do add a 1k in series with the input, then if you then add a 15k resistor from the input pin to GND, creating a slight voltage divider, then that will attenuate the 3.5V to 3.28V. Then you get both the negative current limiting and bring the input within specified range.