I know it is old thread, but just to add my 2c.
I have worked with this chip and here is my findings that i reported to TI with no real response...
Conclusion: Input hold switch is faulty (leaks)...
Solution, dont use this chip (i made my own solution)...
Below is copy paste of my report to Ti support year about 11/2010
[Problem:
I want to use ACF2101 for integrating amplifier, but it want stop integrating, it has 30usec of flat (hold) but after that it continues to integrate... My investigation blames mos switch at input, it does not cut off! Current swing loaded with 10Kohm resistor to the plus power (i can send you test setup schematic) is from 900uA to 800uA, and it should cut off totally (according to data sheet off state gives equivalent resistance of 1000Gohms, which should keep the off current below the 10pA range.) Can you please look into it. What is the ESD sensitivity of that mos switched input (considering that gate is not exposed). Is that normal, i see that at two chips so far. We bought 10 of these chips for prototyping purposes. Can i have exact schematic of the chip?]
I have worked with this chip and here is my findings that i reported to TI with no real response...
Conclusion: Input hold switch is faulty (leaks)...
Solution, dont use this chip (i made my own solution)...
Below is copy paste of my report to Ti support year about 11/2010
[Problem:
I want to use ACF2101 for integrating amplifier, but it want stop integrating, it has 30usec of flat (hold) but after that it continues to integrate... My investigation blames mos switch at input, it does not cut off! Current swing loaded with 10Kohm resistor to the plus power (i can send you test setup schematic) is from 900uA to 800uA, and it should cut off totally (according to data sheet off state gives equivalent resistance of 1000Gohms, which should keep the off current below the 10pA range.) Can you please look into it. What is the ESD sensitivity of that mos switched input (considering that gate is not exposed). Is that normal, i see that at two chips so far. We bought 10 of these chips for prototyping purposes. Can i have exact schematic of the chip?]