MSP430G2231: ADC Input Impedance.. Buffer or no buffer required for high impedance connection to ADC Inputs..

Hi Team '430,

My customer wants to connect an analog input w/ an extremely high input impedance directly to the ADC w/ no OpAmp/Buffer.. any issue w/ this? 

Detail below..

Does the MSP430G2231 ADC require an Op Amp buffer between the circuit below and the '430 ADC inputs?

Can it be fed from a 10M/7.5M voltage divider with 6.8nF to ground like shown below w/o issue?

• What is the dynamic range of the input.. is it simply a static level? 
  “Almost” static DC levels, measuring battery voltage at maybe only a 1 second sample rate.  The battery voltage will rise and fall over time and load conditions.
• Why are the divider R’s so high resistance?
  An attempt to not load the battery at all, so that the divider has no appreciable current drain at all.
• What makes you think you need an Op Amp buffer (which documentation)?
  Generally when I have designed interface circuits for various microcontrollers with SAR ADC’s, they generally recommend using an Op Amp buffer to lower the source impedance.  I am concerned here with there being no buffer, and an extremely high source impedance of 10M||7.5M.  The only thing I see even remotely related to this is in section 22.2.5.1 Sample Timing Considerations of the MSP430x2xx Family User’s Guide (SLAU144J), discussing mainly settling time.  They don’t want to add an Op Amp because of additional parts and current.  What is TI’s recommendation ?

Thanks, Merril