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TLV7031-Q1: Output does not toggle

David Fishman
Intellectual 495 points

Part Number: TLV7031-Q1
Other Parts Discussed in Thread: TLV1805, TLV7031

Hi,

The part is used in a +5V circuit with an input range of 200mVpp to 5Vpp. The part is configured for non-inverting hysterisis with a 5k resistor on the +IN and a 1M feedback resistor. A 2.5V reference is connected to the -IN.

When the signal, which is 220kHz, is connected to the Input is larger than ~2Vpp, the output goes to the +5V rail and no longer toggles with the input. Below 2Vpp the output toggles but the duty-cycle is not 50%.

The same circuit worked well with the TLV1805 comparator with the same external components connected the same way, but to different pins numbers are the pinout is different.

I'm wondering why the TLV7031 is not working.

Thanks, Dave

  • 0
    TI__Guru 69536 points

    Hi David,

    You are pushing the limits of the TLV7031. This is a nano-power device and is slow. 125kHz is the theoretical limit (Fmax).

    Fmax = 1/(TPLH + TPHL) = 1/(4us + 4us) = 1 / (8us) = 125kHz

    1 / 250kHz = 4us, 4us/2 = 2us.

    You need a comparator with <2us response time. That is the *theoretical* minimum response time.

    If you want the edges to be clean and symmetrical, I would look for a device with <1us. The faster, the cleaner the output, but at the expense of supply current.

    Is supply current critical? Size?

    I would recommend trying either the TLV1811-Q1 or TLV3511-Q1. Both have the same pinout as the TLV7031 can can drop-in replace.

  • 0
    Intellectual 495 points

    Hi Paul,

    Thank you very much for your quick and helpful guidance.

    I was wondering why the LTSpice simulation, using the TI provided Spice model, did not show any degradation at the output even at 1MHz.

  • 0 in reply to David Fishman
    TI__Mastermind 27660 points

    David

    thanks for your post and support of the forum.  Ideally our macro-models would be able to mimic this dependency of signal swing but at this time they do not.  Almost seems like we would need to have more of a transistor-based model in order to capture this effect.

    Chuck