Top Mall-Fi poster. The T in META42. Formerly with Tangentsoft Parts Store
Sep 27, 2001
On the PPA battery board, R4 and R5 form a voltage divider across the battery pack. The batteries discharge through this divider, so it contributes to the speed at which the pack self-discharges. Previously, my configuration calculator kept the resistor divider in the tens of Kohms range, but I've been experimenting and have found you can get it up into the 100's of Kohms range and have it still work. When the divider is this high, the divider's contribution to the pack's self-discharge time is insignificant.
You have to be careful not to make the resistor values too high, though, or the Vsen pin's bias current will start to cause problems.
I've improved the configuration calculator to take these considerations into account, and the suggested configurations section uses new values.
If you're happy with your current battery board performance, by all means, leave it alone. But, if you'd like to tweak it, I'd appreciate hearing whether higher values work out in your setup.