I am having a bit of a hard time understanding the voltage read in the voltage divider that is being an input for an ADC to an NXP microcontroller, S32K118. Below is the schematic of the circuit.
Where P1 and R1 represent an analogic temperature sensor, just for hardware debugging purposes.
The designed and the real values of each component are represented in the table below:
| Component | Design | Real |
|---|---|---|
| P1 | 10k Ohms | 9.4k Ohms |
| R1 | 4.7k Ohms | 4.4k Ohms |
| R2 | 15k Ohms | 13.4k Ohms |
| R3 | 22k Ohms | 21.9k Ohms |
| C1 | 100n F | 100n F |
According to the MCU (S32Kxx) datasheet, the ADC input impedance equivalency diagram is shown below:
As the signal from the sensor is updated at a very slow rate, I consider the signal being DC, therefore no current flows into the ADC pin and the voltage at the node (R1,R2 & R3) is the same as in the node (R3 & C1).
Then, calculating the voltage divider in both cases, which resistance of the potentiometer was changed from the minimum to the maximum, using the real values, I got the following values:
$$ Vout = \frac{(P1 + R1)}{(P1 + R1) + R2}{Vin} $$
V_{in} = 5V
Vout_{min} = 1.23V
Vout_{max} = 2.45V
However, the values that I am reading with the multimeter are:
Vout_{min} = 0.22V
Vout_{max} = 0.65V
That makes no sense, I have checked all the tracks and components, and they are in order.
Am I missing some point that is leading to misunderstanding something?
