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Original question:

TLV3501A-Q1: Why does the quiescent current of these two comparators(TLV3501A, TLV320x) have so huge difference?

TLV3501A-Q1: What's the meaning of ΔVin & V_overdrive?

Jankel
Intellectual 731 points
Part Number: TLV3501A-Q1
Other Parts Discussed in Thread: TINA-TI, TLV3501

What's the meaning of ΔVin & V_overdrive?

  • 0
    TI__Guru 60016 points
    Hello Jankel,

    "Overdrive" is amount of voltage *above* the reference voltage.

    The delta-Vin is the total p-p voltage if the input signal.

    So, assuming VREF is 0V (gnd)

    For dVin=100mV, and Voverdrive=20mV, the input signal would be -80mV to +20mV

    For dVin=100mV, and Voverdrive=5mV, the input signal would be -95mV to +5mV

    For dVin=100mV, and Voverdrive=50mV, the input signal would be -50mV to +50mV
  • 0 in reply to Paul Grohe
    Intellectual 731 points

    Hi Paul,

    Thank you so much for your reply.

    And there're still some other questions:

    1, If the inverting terminal equals constant 5mV, and noninverting terminal will only be 0V or 10mV in my application (switching freq. between 0mV and 10mV is 300kHz), it's also possible for such a low input voltage level operation, right? (power rail is 5V/0V)

    2, What's the meaning of the wake-up delay in page7 of the TLV3501A-Q1 datasheet?

    3, Pls see the circuit below, if Vin equals 15V, power rail is 5V/0V, the only one resistor is 10k ohm, so the input current is of course smaller than 10mA, and I know from the datasheet that in this condition it seems the inverting terminal will be clamped to 5V by the ESD diode inside the opamp, right? But I got the simulation result of 15V at the inverting terminal in TINA-TI..............

  • 0 in reply to Jankel
    Guru 140200 points
    Hi Jankel,

    if your input signal is only +/-5mV, then you must consider the input offset voltage of TLV3501 of +/-6.5mV. So, it can be, that the TLV3501 is not working properly. I would increase the input signal amplitude: And, as the TLV3501 is very fast, I would provide some hysteresis too.

    The wake-up delay has to do with the shutdown feature. Read section 8.4.1 of datasheet and see figure 8.

    TINA-TI simulation usually works for operating within the specified common mode input voltage range. So, when the input signal exceeds the supply rails this might not be simulated correctly.

    Kai
  • 0 in reply to kai klaas69
    Intellectual 731 points

    So, if my input signal is only +/-10mV, it will work properly, will it?

  • 0 in reply to Jankel
    Guru 140200 points
    Hi Jankel,

    yes, it should, at least in theory. But I would increase the input voltage swing and, even more important, I would add a hysteresis. Remember that the TLV3501 is an ultra high speed comparator!

    Kai
  • 0 in reply to Jankel
    TI__Guru 60016 points
    Hi Jankel,

    If the input is +10mV and -10mV around the reference voltage, you have a 10mV overdrive, which according to the front page will give you a response time of 6-7ns.

    However, the TLV3501 has built-in 6mV hysteresis, with a ±6.5mV maximum offset, so the maximum thresholds would ±6.5mV + ±3mV, or ±9.5mV - so you are right on the edge of detection.

    As Kai said - try to get as much signal into the input as possible. The "harder" you drive the input, the faster it will respond.
  • 0 in reply to kai klaas69
    Intellectual 731 points

    Hi Kai,

    but TLV3501 has build-in 6mV hysteresis, do you think it is enough?

    I don't know if I need to add extra hysteresis.

  • 0 in reply to Paul Grohe
    Intellectual 731 points

    Hi Pual,

    "...try to get as much signal into the input as possible..."
    Of course, but trade-off.
    My input signal is from the PFC current sensing circuit, so you know this kind of signal must has some time period that the voltage of the sensed signal is around 0. What's more, it'll affect the PF/THD performance of the PFC.

    In addition, as I also asked Kai just now,
    do you think the build-in 6mV hysteresis is enough?
    I don't know if I need to add an extra hysteresis.

  • 0 in reply to Jankel
    Guru 140200 points
    Hi Jankel,

    as I already said: In a perfect circuit with noisefree and steep edges it MIGHT work. But in a real application you have always noise and interference from switchings superimposed on the wished signal. And this can totally ruin the performance of comparator. I think the built-in 6mV hysteresis is needed to make the comparator even run with perfect signals...

    So, yes, I would definitely add a hysteresis of some dozens of millivolt. I even do this with comparators which are much slower and have a much higher wished signal.

    Kai
  • 0 in reply to Jankel
    TI__Expert 4555 points
    Jankel,

    Do you have any other concerns or questions regarding the topic of this thread? If not, we will close this thread soon.

    Regards,
    Jonny