TLV3401, TLV3402 - Output behavior at power up

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:

http://www.ti.com/lit/ds/symlink/tlv3691.pdf

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