Reference voltage for the ADC module in NRF9160 SiP?

[xuan0802]

Dear guys, 

I am implementing a module that monitors the battery voltage for our tracker device using NRF9160.

I do not understand how to set up two parameters for the ADC, those are ADC_GAIN and ADC_REFERENCE.

In the sample, these two parameters are set as followings:

#define ADC_GAIN ADC_GAIN_1_6

#define ADC_REFERENCE ADC_REF_INTERNAL

Our battery voltage is from 3V to 4.1V, we are using a voltage divider, so the battery voltage goes to AIN pin is from 1.5V to 2V.

With our above battery, what are ADC_REF_INTERNAL and ADC_GAIN? and how to set ADC_REFERENCE properly to measure our battery voltage?

[Håkon Alseth]

Hi,

 

#define ADC_GAIN ADC_GAIN_1_6

#define ADC_REFERENCE ADC_REF_INTERNAL

This means that the input is divided by 6, and the reference is the internal 0.6V reference.

The maximum input is REF / GAIN, in this case: 0.6 / (1/6) = 3.6V. Provided that this is within VDD_IO + 0.3V.

 

 

Our battery voltage is from 3V to 4.1V, we are using a voltage divider, so the battery voltage goes to AIN pin is from 1.5V to 2V.

 In the case that the input is max. 2V, you can use a gain of 1/4, which will give a maximum of 0.6/(1/4) = 2.4V input voltage.

 

Kind regards,

Håkon

[xuan0802]

Internal reference voltage is stable right?

Thanks you very much.

[Håkon Alseth]

There is no dedicated specification on the reference voltage itself, but; the SAADC electrical specification (gain errors etc) covers using internal reference:

https://infocenter.nordicsemi.com/topic/ps_nrf9160/saadc.html?cp=2_0_0_5_11_10_0#unique_2025699942

Kind regards,

Håkon