If you want to characterize accuracy, precision, noise, linearity and ENOB of the ADC like they do in the datasheets I can give you a hand. It is a nice way to check the specs of the fully assembled system. It is part of my job routines.
Bin | Frequency |
60635 | 4 |
60636 | 1970 |
60637 | 3026 |
Oh hey @Cal, I had no idea you'd been noodling on BMSs over in this thread!In the mean time I determined a simple way to check adc noise and linearity
Could you post both measurements? I mean cell voltage before the system and cell voltage after the OPA. I just want to check if it is related with the MUX non linearity that we discussed looooong ago.The OPA991 op-amp does not accurately reflect cell voltage. For cells 1 to 4 op-amp is -10, 64, 64, 56 mV off.
As the protection diode is conducting the ADC provably is delivering too much current and the short circuit protection is being activated. Maybe that is the reason your ADC is crying.These diodes have normally 0.7V droput voltage so when the input (PIN in the figure) is higher than the supply 3.3V (VCC in the figure) the diodes will start conducting from 3.3+0.7=4V. Your ADC is applying 5V so the protection diode is conducting.
Are the "simulated" cell voltages measured while the mux is selecting them? If your resistor stack used to simulate cells is not really low resistance, then when the mux selects it, you'll change the result by drawing more current through the input of the op-amp circuit.I have 4 330 ohm resistor to simulate the 4 cells.
The voltage across each resistor is: 3.294, 3.294, 3.292, 3.296V
The output of the adc (which is a good representation of actual input voltage) is: 3.284, 3.358, 3.356, 3.352V
No! There's no challenge there. Nothing to learn.Have you thought about using a pre-made cell monitoring IC like the Analog Devices ADBMS1818?
All the ADC stuff is taken care of with cell voltage and current measurements, and it has the mosfets for passive balancing integrated in it, as well as inputs for thermal sensors.
I mean there's still quite a bit to learn lol, you still need to interface with an MCU and handle your charge and discharge MOSFETs somehow.No! There's no challenge there. Nothing to learn.