Battery Monitoring on ADC pin of nRF9160 Module.

[Shashikant]

Hello All,

We are designing a Tracking device system, for this we use nRF9160 LTE+GPS combo module. this system is battery operated so we need to monitor the battery continuously. here we use 1000 mAH Li-Po.

We design a power supply circuit, that can give 3.8V/800mA output current to VDD and 3.3V/250mA to VDD_GPIO of nRF9160.

We have a following some queries regarding the nRF9160 module mentioned below. 

1) We want to measure voltage of Li-Po battery using nRF9160 so kindly provide the best divider circuit which draw the less current, if possible share the reference circuit for voltage divider.

2) We are providing 3.3V at VDD_GPIO pin, so is it possible to use internal reference voltage for ADC.

3) How to configure internal and external reference voltage of ADC calculation.

4) what is maximum external reference voltage that can we give for ADC?

5) what is the overall maximum supply current capacity for VDD_GPIO?

6) We gives 3.8V/800mA supply current to nRF9160, is it sufficient?

Thank you

[Håkon Alseth]

Hi,

 

The ADC peripheral in the nRF9160 is the "SAADC", which is similar to the nRF52-series "SAADC" as well.

There's several threads/blog posts regarding battery measurements in general on the nRF5-series devices:

https://devzone.nordicsemi.com/nordic/nordic-blog/b/blog/posts/measuring-lithium-battery-voltage-with-nrf52

https://devzone.nordicsemi.com/nordic/nordic-blog/b/blog/posts/measuring-lithium-battery-voltage-with-nrf51

https://devzone.nordicsemi.com/f/nordic-q-a/324/how-to-measure-lithium-battery-voltage

 

2) We are providing 3.3V at VDD_GPIO pin, so is it possible to use internal reference voltage for ADC.

Yes, if you set the gain to 1/6 and use the internal 0.6V reference:

https://infocenter.nordicsemi.com/topic/ps_nrf9160/saadc.html?cp=2_0_0_5_11_9_31#register.CH-0-7.CONFIG

 

This should give you a ceiling of 3.6V (or VDD_GPIO +0.3V) 

3) How to configure internal and external reference voltage of ADC calculation.

Please see the linked threads above. 

4) what is maximum external reference voltage that can we give for ADC?

 This depends on your configuration. You cannot sample outside of VDD_GPIO (and lower than GND), as explained more in detail here:

https://infocenter.nordicsemi.com/topic/ps_nrf9160/saadc.html?cp=2_0_0_5_11_6#concept_kxz_4pp_qr

5) what is the overall maximum supply current capacity for VDD_GPIO?

 VDD_GPIO's current consumption will depend on how much current you draw from your GPIOs. For GPIO el.specs, please see this chapter:

https://infocenter.nordicsemi.com/topic/ps_nrf9160/gpio.html?cp=2_0_0_5_3_4#unique_1619065902

6) We gives 3.8V/800mA supply current to nRF9160, is it sufficient?

 This will heavily depend on how much current you plan to source/sink through your GPIOs, but given the peak currents of the modem, it looks to be within:

https://infocenter.nordicsemi.com/topic/ps_nrf9160/_tmp/alta.nRF9160/autodita/CURRENT/parameters.id_current_modem.html?cp=2_0_0_4_1_0_13

 

PS: there's an simple adc sample for 91 available here: https://github.com/Rallare/fw-nrfconnect-nrf/tree/nrf9160_samples/samples/nrf9160/adc

 

Kind regards,

Håkon