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Excessive offset voltage

Category: Hardware
Product Number: ADCMP600

I'm seeing signs that the ADCMP600 comparator in my circuit has an offset voltage 1) far in excess of the +/-5mV spec in the datasheet, and 2) seems to be increasing with time. 

I will post a full circuit schematic later today but here are some of the details:

  • The circuit in question uses the ADCMP600 to sense voltage across a current-sense resistor (measuring current through a BJT switch), and if it exceeds a defined threshold (1.5V) to turn the switch off
  • Initially when I first powered the circuit the offset voltage while too high was relatively small (it was tripping at Vneg=1.4V when Vpos=1.44V, so Voffset=40mV)
  • Over time, the offset has grown to the point where the comparator output now switches off when Vneg=1.05V (Vpos is still 1.44V so Voffset is now about 400mV)
  • The slew rate of the input signals is not particularly fast so I don't think various factors like uncalibrated skews in my measurement setup are to blame

My main question is whether this condition of excess Voffset is a sign that 1) I have a bad part, or 2) my circuit has somehow damaged the part

A snippet of the relevant schematic is below. The affected ADCMP600 is the one in the upper right (the lower left one is a relaxation oscillator and is working as expected). I've also included a scope capture showing TH (Yellow trace) vs. CS (Red Trace). Due to the hysteresis in the circuit the TH shifts from about 1.44V to close to 0V at the trip point. The scale and offset of the 2 channels is the same to clearly show the large offset voltage that the ADCMP600 is triggering at.

Added schematic and scope plot
[edited by: muse-ee at 1:59 PM (GMT -4) on 20 Jul 2022]