Li-Ion Battery voltage measurement

[AimHigh]

Hi,

Good day! I hope everyone is doing well.

I have a weird problem measuring Li-ion battery pack voltage.

Problem: Tried to measure battery pack voltage 12.6V using a resistor divider (R1 604K, R2 191K 1% tolerance). But I kept getting wrong values for instance at 11.91V Batt Voltage at R2 out is measured at 2.5V. Theoretically, it should measure 2.861V. I tried measuring it with multimeter was getting incorrect values and I tried to connect the same voltage divider to voltage controlled source and still got the same values i.e. at 11.91 input R2 out is 2.5V.

Appreciate it if someone could give possible suggestions here.

[hmolesworth]

If Rladder P or N were accidentally enabled the results would be far worst, even more if any pull-up or pull-down were accidentally enabled. The most likely issue is therefore charge time, assuming there is a disturbance on the input prior to sampling (maybe SAADC was off or sampling another channel). To test that theory simply double (or suitably increase) the sample window; for the impedance you mention of 200k-ish a minimum sample time is 15uSecs in any case, often best to start with max sample time and reduce to observe the affect:

// TACQ [μs] Max i/p kOhm
// ========= =============
//     3          10
//     5          40
//     10        100
//     15        200
//     20        400
//     40        800

Maybe post the SAADC settings in use if this doesn't magically fix anything ..