AnsweredAssumed Answered

LTC2945 supply setup for negative voltages

Question asked by Dan.Hintz on Aug 1, 2018
Latest reply on Aug 2, 2018 by Dan.Hintz

I have several negative supply voltages I need to monitor (-2V, -5V, and -30V).


Looking at the block diagram (p. 9)... if I'm connecting the negative supply to the GND pin, am I correct in assuming I'll need optical isolators for I2C in all cases since the internal "ground" on those pins will now be <0V (zeners tripping), or is the control logic somehow isolated?


The few negative-supply examples show INTVCC with only a bypass cap to the GND pin (i.e., no separate supply on INTVCC) for cases where the supply voltage is better than -4V.  For my low-voltage case (-2V), do I need to provide a separate -5V supply to INTVCC for the internal logic, or is there another way around?  I assume the same rules apply to the I2C lines (if I use a -5V INTVCC supply, I'll need isolators pulled to -5V, as well).


Thinking in negative voltage does something horrible to your brain ;-)