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TLV3401, TLV3402 - Output behavior at power up

Guru 19775 points
Other Parts Discussed in Thread: TLV3401, TLV3402, TLV3691

Hi Team,

Please allow me to ask you the output behavior of TLV340x during power up. We sometime see output dip on OUT pin during power up. Is this normal operation ? Why would this happen ? Power on reset ?

I apologize asking you the operation under recommended minimum VCC, however, I would be grateful for your help.

Best Regards,

  • Kawai-san,

    Most comparators, including the TLV3401/TLV3402, do not have power on reset (POR) circuitry and the output can change state during the start-up time. That happens because as the supply moves up from 0 V, and until it crosses above the minimum supply operating voltage (2.5 V for the TLV3401), the internal circuit nodes are powering up to their operating levels. The output state is not controlled and is uncertain during that time. Once the supply voltage reaches the minimum operating level the comparator will assume normal operation, compare the voltage levels present at the two inputs, and decide the comparator output state. The TLV3401 supply voltage has only reached about 1.3 V when the output pulls low during start-up. However, by time V+ reaches about 1.7 V, the output attains the correct state.

    TI does have a more modern, very low power comparator that has built in POR, the TLV3691. The output is a push-pull stage, instead of the open-drain like the TLV3401, but that usually isn't an issue for many comparator applications. You can see the data sheet here:

    The TLV3691 output stays low until V+ reaches the minimum supply operating voltage. Then, the output state decision is made.

    Regards, Thomas

    PA - Linear Applications Engineering

  • Hi Thomas-san,

    Thank you very much for your prompt reply and detailed explanation.

    Best Regards,