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Original question:

TLV3501: TLV3501 OUT pin pull up resistor

TLV3501: output level when inputs are the same ?

Quyen Dang Cao
Prodigy 10 points

Part Number: TLV3501
Other Parts Discussed in Thread: TLV7011

Hi, the inputs in my circuit is very low at inital stage (~0.015V), the output is high (3.3V), is there a problem ?

I need a low-level output at beginning, could you suggest a solution ?

by the way, in the datasheet, R1 should be 51k Ohm, not 51 Ohm, right ?

  • +1
    Guru 140200 points

    Hi Quyen,

    choose a comparator with built-in power-on reset (POR).

    And, no, it should not be 51k but 51R, indeed.

    Assume Vref is 2.5V and Vcc is 5V. Then

    Vcc - Vref = 2.5V

    and

    2.5V / 10051R x 51R = 12.7mV

    So when the output of TLV3501 toggles from high to low or vice versa, the voltage at the +input of TLV3501 shifts by +/-12.7mV, according to a hysteresis of 2 x 12.7mV = 25.4mV.

    Kai

  • +1 in reply to kai klaas69
    TI__Mastermind 27480 points

    Thanks again Kai for your excellent support.

    Quyen

    Kai is suggesting you use a comparator with a POR circuit that will provide a known startup value at the output of the comparator when the power supply is ramping up to the recommended operating voltage.  A good option if you do not require the speed of the TLV3501 would be the TLV7011.  However, if you need the speed of the TLV3501, please share your waveforms on an oscilloscope capture so we can better support you use case.  You mention a low input voltage but I am not sure exactly what you mean.  Please show both inputs, the output, and the power supply in your plot.

    Thanks again for your support of TI.

    Chuck

  • 0 in reply to Chuck Sins
    Prodigy 10 points

    hi Chuck Sins, in general, I want to make clear the state of output when the inputs are in hysteresis range, for example, V+ >V- but (V+ - V- )< hysteresis value, so what the stage of Vout ?

  • 0 in reply to Quyen Dang Cao
    TI__Mastermind 27480 points

    Quyen

    If the output is in the high state, the output will remain high until the inputs differentiate by more than 6mV (typical hysteresis level) in the negative direction. Likewise, once the output is in the low state, the output will remain low until the inputs differentiate by more than 6mV in the positive direction.

    Chuck