ADCMP hysteresis control

hi,

I am designing in ADCMP572 for a physics research application (time-of-flight counter for cosmic ray particles). The input signal consists of random pulses, including many just grazing the threshold level. It will be necessary to use some hysteresis, yet we also have to be careful about having stable thresholds and the minimum practical value of hysteresis. Ambient temperature in the application may vary from roughly -40 to +60 deg C. A programmable hysteresis seems wise, as the most practical way to optimize it and to afford some workaround in case of surprises.

This leads to two important questions:

Q.1. I will control the hysteresis with a current source 0 - 300 uA or so. (30 mV is definitely plenty.) If I have a temperature-independent current source, will the hysteresis be reasonably temperature-independent? (Goal: Comparable to the offset voltage tempco, 10 uV/degC per the datasheet.) Or should I be desiging some temperature compensation in this current source?

Q.2. The ADCMP572 will be powered from +3.3 V to ground. I have a negative supply available (needed for other circuits) so the most obvious way to do a good current source for hysteresis control current is to use that. Is it safe to pull the hysteresis pin down with 300 uA even if ADCMP VCC=0? I could of course add some clamp diode, but I am guessing there is one internally and 300 uA will not break anything. This seems to be confirmed in Abs Max ratings table, but I'd like to hear some more on this.

Thanks,

     Gerard

  • Hello,

    I am just asking here, is there any chance of a reply on this, especially question 1, please? If someone from ADI is reading this and knows the correct experts to ask for this part, please point them to my questions.

    By the way I see that I screwed up in the title of the original post which should have been "ADCM572 hysteresis control" of course.

    Thanks, sincerely,

       Gerard