Capacitor value at ADC input for nRF52?

[Luis]

Hello, Does anyone know if the information and methods given in the links below are still valid for nRF52?

devzone.nordicsemi.com/.../

devzone.nordicsemi.com/.../

If they are still valid, what values should I use for nRF52? If they are not valid, any idea on how to adapt them for nRF52?

Thanks!

[Stefan Birnir Sverrisson]

Hi

The information given for the nRF51 are not valid for nRF52 because the ADCs of this two ICs are of different type. You should not connect a capacitor for nRF52 SAADC but you should configure the SAADC acquisition time depending on what source impedance you have. According to SAADC electrical specification, you can have maximum 800kohm source impedance when configuring the maximum 40us acquisition time.

So to adapt the voltage divider method for nRF52 SAADC:

• Don't connect a capacitor
• Configure SAADC acquisition time according to source impedance, which is the size of resistor R_1, with maximum value of 800kohm

Update 23.5.2016 Here is fresh information on how to measure lithium battery voltage with nRF52 SAADC

[Luis]

Wow, that's great news. Then how do I know max sample rate? Using adquisition time + conversion time? What is the difference between using internal reference or VDD as reference? And should I still design my resistor bridge for the 1.2V range? Because that would be internal reference and 1/2 gain, but datasheet says 1/4 gain has less error? Then should we use 2.4 V range? Considering my Vdd is 3.3V, in terms of noise, accuracy and resolution.