Hello,
There are many questions out there on correctly determining the SAADC pin input voltage limits. The equations given in the product spec is very straight forward:
Input range = (±0.6 V or ±VDD/4)/gain
It also mentions that a gain of 1/6 is available. This would mean that if you are using a reference of VDD/4 and a gain of 1/6 that your voltage limits would be +/- 1.5*VDD.
This would be a very useful feature for me as I have a sensor that is processed through an instrumentation amplifier configured at its lowest gain and I still have a signal that is 0-2.5V.
I am powering the device through VDDH with 4.5V and my VDD is 1.8V and I don't have room to go much higher.
Unfortunately, it also states in the product spec: "Inputs AIN0 through AIN7 cannot exceed VDD or be lower than VSS" which to me means that even after
applying this equation I am still range limited to 0-VDD. Is this true? I also noticed that the IO pin limits in the Absolute Max Ratings are VDD+0.3. Does this mean that I can apply a gain to allow me to accept analog input up to VDD+0.3? Is is possible to measure an analog voltage that is greater than VDD using the nrf52840?
What would the best way be to get this signal into the nrf52?I am really trying to keep my SNR as high as possible. Open to other non-nrf solutions as well. It seems the real root of my problem is that I want to amplify the signal to keep SNR high but then need to attenuate it to get into the MCU. This seems like I am going to lose all of my gains from my amplifier. Any advice would be appreciated.
Thanks!
