Lpc2000

Perhaps buffering with a one-gain op-amp could help? (e.g., LP339).

The problem, as I see it, is that you shouldn't present any voltage to 
the A/D inputs while the chip is out of power. In fact, you can't tell 
if those pins are connected to the A/D block when VDD is 0!

Anyway, by the same manual, you can use a 40K resistor which will give 
you *some* protection (~82µA).

Guille

--- In lpc2000@yahoogroups.com, "myfriendmarkis" <myfriendmarkis@...> 
wrote:
>
> I'm using the LPC2148 and have a serious problem. I'm using one of 
the 
> ADC channels to measure battery voltage (across 2AA cells). When the 
> microcontroller is off there is a current drain path from the 
> batteries through the ADC which flattens the batteries in a few days 
> with the board off.... 
> 
> The input impedance of the ADC is shown as 20k ohms so it is not 
> possible to put a large resistor in series... Please can you help?
>