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LMV762 failure at low temperatures

Other Parts Discussed in Thread: LMV762, TLV3492

Hello,

Although the two comparators of LMV762 are built on the same chip, their behaviour is not similar in our circuit. When the temperature drops below approx. +5 degC, one of the comparators (pin 1) does not deliver pulses anymore.

We tested this circuit many times and finally we decided to solder 1 inch long wires on chip's pins so it can stay in an elevated position from the printed circuit board. Then, we put the whole assembly outside, when the temperature was approx. 0 degC. Pin 1 was not generating pulses unless we slightly heated up the chip, by placing a soldering iron tip close to the chip. Then, we changed the chip and had the same result.

We ended up replacing LMV762 with TLV3492 in the same circuit and it worked fine even at -20 degC, but still the question is not answered.

Can this be related to the way we are using the circuit (power, input bias, common mode rejection etc.)? Your feedback on this matter will be highly appreciated.

  • Hello Mircea,

    The LMV762 is not a rail-to-rail input. You are violating the upper input common mode range.

    The limit is 1.3v below V+, or 2V on a 3.3V supply. Your discrimination threshold is beyond the limit. The limit changes with temperature....as you have found.

    Comparators can usually handle this if ONE input is still within legal range, but BOTH the inputs are outside the limit - which is indeterminate.

    The TLV is a Rail to Rail input, so it does not have that issue.

    So you will either have to lower the levels, or use the R-R input device.

    Regards,
  • Thanks, Paul. I should have noticed that. I do appreciate your answer.