Maximum voltage clarification on nrf52 analog pins

RE: Maximum voltage clarification on nrf52 analog pins

jgartrel — Thu, 01 Dec 2022 19:24:03 GMT

Jared, thank you very much for the help.

FWIW, I tested this today on an nrf52840 with input range configured as (0.6 V)/(1/6). I seemed to get quite accurate results when the external pin voltage was in the range of VDD to VDD+0.15V (no difference in the normal error margin in that range). All values measured were in the range of VDD to VDD+0.15V. I did not test it beyond VDD+0.15V. The nrf52840 still seems to be in a healthy working condition.

RE: Maximum voltage clarification on nrf52 analog pins

Jared — Thu, 01 Dec 2022 15:06:51 GMT

[quote user="jgartrel"]

the SAADC input range is configured as (VDD/4)/(1/4), I should reliably read 2.5V (max value) from the SAADC, correct?

[/quote]

Correct.

[quote user="jgartrel"]If the SAADC input range is configured as (0.6 V)/(1/6), I should reliably read a value between 2.5V and 2.7V, but that value will become increasingly inaccurate as the voltage to the pin approaches the 0.3 V threshold of the ESD protection, correct? Does unreliable mean the SAADC would ever report a value below 2.5V?[/quote]

No, you'll still be limited by VDD = 2V5. You can not read a value reliably that is over VDD or under VSS. Unreliable means that we can't be sure what the SAADC will return, This also means that I can't answer whether the SAADC will report a value under 2.5V when you measure a value over VDD. Most probably not, but I'm not sure If we have tested it, since it's outside the specification.

regards

Jared

RE: Maximum voltage clarification on nrf52 analog pins

jgartrel — Wed, 30 Nov 2022 15:24:21 GMT

Perfect, thank you!. But that leads to a follow up question: can you clarify what you mean by unreliable?

So, in a scenario where VDD = 2.5V and 2.7V is applied to the pin ( which should be safe ), and:

the SAADC input range is configured as (VDD/4)/(1/4), I should reliably read 2.5V (max value) from the SAADC, correct?
If the SAADC input range is configured as (0.6 V)/(1/6), I should reliably read a value between 2.5V and 2.7V, but that value will become increasingly inaccurate as the voltage to the pin approaches the 0.3 V threshold of the ESD protection, correct? Does unreliable mean the SAADC would ever report a value below 2.5V?

RE: Maximum voltage clarification on nrf52 analog pins

Jared — Wed, 30 Nov 2022 13:14:54 GMT

Hi there,

For the measurements from the SAADC to be reliable, the input range can not exceed VDD or be lower than VSS.

[quote user=""]For example if VDD = 2.5V, is it OK to have a pin voltage of 2.52V for a SAADC input (AIN0-AIN7)?[/quote]

The pin will not be damaged by this as it's under the VDD + 0V3 constraint, but the measurement will not be reliable since it violates the second constraint.

regards

Jared