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ADC Input Current Sensitivity

Seth Berggren
Intellectual 910 points

Other Parts Discussed in Thread: CC2540

Hi,

I am designing a circuit using the ADC on the CC2540 that will measure battery voltage (for a car battery). These voltages could range from 12V to 60V so I am using a divider, factoring in the internal resistance of the ADC, which, according to the datasheet, is 197KOhm. So, I put a 1400KOhm resistor at the input of the ADC to reduce the voltage by a factor of 8, bringing 12V to 1.5V. To protect the circuit, there are two TVS diodes, one that limits the battery voltage to 30V, and the other limits the voltage at the input of the ADC pin to 3V. I attached a picture of the diagram:

With this massive amount of resistance, the current entering the pin is maximum of 15 uA. Is this enough for an ADC to work? How low can I go?

Thanks