LTC2508

The only way to inject 30mA into the In+ input is by exceeding the absolute maximum rating for In+. The data sheet clearly states that exposure to any absolute max rating condition for extended periods may affect device reliability and lifetime.

Thanks for the reply!

" The only way to inject 30mA into the In+ input is by exceeding the absolute maximum rating for In+" is it because the absolute maximum for Analog Input Leakage Current is 10nA or because the absolute maximum for Digital Input Current is 10uA?

your statement is absolutely right according to Note.1, on the other hand, Note.3. says "This product can handle input currents up to 100mA below ground or above REF or OVDD without latch-up". 

The 100mA input current is allowable only for a very short time. The power dissipation at 100mA input current will exceed the 500mW absolute maximum power rating with a 5V reference. 

The 100mA input current is allowable only for a very short time. The power dissipation at 100mA input current will exceed the 500mW absolute maximum power rating with a 5V reference. 

Thank you,

Can I ask why are you stating this: " The only way to inject 30mA into the In+ input is by exceeding the absolute maximum rating for In+" ?

The In+ input (See Figure 3 of the data sheet.) goes straight into a 45pF capacitor except for protection diodes that are normally reverse biased. The only way to draw any significant current into the input is to take the input voltage above REF or below ground. Exceeding REF or ground by more than 300mV exceeds the absolute maximum ratings for the LTC2508-32.

So it means that I was biasing the In+ with a negative voltage (e.g.-1 V) and that's why I had 30mA going into In+, and its damaging the ADC, but if I have any positive voltage on In+ (e.g. +1V) for a long period of time, the ADC will be fine.

If REF has power applied, then a +1V input voltage on IN+ will not cause any problems for the ADC.