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Reading ADC without voltage divider

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chota.sanjiv:
Hi Guys,

I have a 13S li-ion pack which powers my BMS MCU (CY8C58LP) after proper regulation, I want to read the voltage of individual cells via the ADC. One method which I could think of was using appropriate voltage dividers to bring the voltages within analog sensitivity range for every individual cells. The second method may be to use a mosfet based mux to switch the VDDA and VSSA to each individuals cell +tive and -tive and then read using ADC, but I am not sure if this is possible or what kind of impact this will do if I switch the analog ground dynamically.

thanks
Sanjeev

Kleinstein:
Switching the ground only works if the ADC and related µC has an independent supply.

There is a similar method that can work with a common supply: use CMOS switches to charge a floating capacitor as a kind of sample and hold stage. And than bring both sides of the capacitor down to the ADC and ground. One still has to make sure the wrong switches are never on at the same time.

chota.sanjiv:
Thanks for the response, I am attaching the electrical spec of the MCU. The specs for VDDA and VDDD gives a indication that the they are independent however VSSA specs ties it to +-0.5v of the VSSD.

Zero999:

--- Quote from: chota.sanjiv on December 26, 2018, 09:47:55 pm ---Thanks for the response, I am attaching the electrical spec of the MCU. The specs for VDDA and VDDD gives a indication that the they are independent however VSSA specs ties it to +-0.5v of the VSSD.

--- End quote ---
They're not isolated, hence the need for them to be within 0.5V of each other.

As mentioned above, the only way to do as you've described is to run the MCU off an isolated power supply, such as a separate battery or DC:DC converter.

Mechatrommer:
another way is differential amplifier...

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