Current consumption increases with decreasing the input voltage

[venkatesh dyagala]

Hi Team,

We are using nRF52840 DK with sensors. We developed a custom code that is working fine. But the issue is current consumption. Showing below the readings.

The supply is given through the external input supply(P21), moved the SW10 to ON, Moved the SW6 to nRF only

• With 3.3 input voltage observed peak 4.53 mA
• With 1.8 input voltage observed peak 6.85 mA

Then why the current consumption increases with decrease in input supply. Not only peak the average current consumption also increases.

Then I read the answer regarding this issue at https://devzone.nordicsemi.com/f/nordic-q-a/30320/nrf52-current-consumption-in-relation-to-supply-voltage.

But now I would like to know that we will measure the battery life based on the numbers which we get at 3 v, if as the battery discharges the board consumes more power where the battery is critical and the life span we expected will decreases drastically. so how we can conclude this?

As Nordic mentioned that operating voltage is 1.8 to 3.6 so when we give the supply with in the range the current consumption should not alter right. 

Thanks,

venkatesh

[Simonr]

Hi

Please see the picture below. This is a typical battery discharge graph. As power always must stay the same when powering a device, the current consumption will increase as the voltage decreases. As you can see, a battery's voltage drop is generally very low until the end of its lifetime, so the current consumption should be fairly stable throughout its life cycle. Generally, it is stated in a battery data sheet how long it will be able to supply X volts I believe, so you should look at that to get a better idea.

Note that this is just a typical voltage curve, so it will likely differ depending on what battery you are using. Don't hesitate to ask if you have any further questions.

Best regards,

Simon

[venkatesh dyagala]

Hi,

Its okay with the battery consumption, But by looking into the datasheet of nordic. I observed that there is in increase in current consumption with decrease in voltage. I would like to know the exact reason behind it. 

In soc some of the components works on 3v. When we give 1.8v as input the regulators will convert the 1.8 to 3.3 and give them as input to the respective components, does the conversion taking much consumption ? or else any other component causing the issue ?

Attaching the graph showing the current consumption with increases with decrease in voltage

 

[Simonr]

Hi

This is the nature of how a DCDC regulator is working. A DCDC regulator will be more efficient the higher the input voltage is, as it'll need to consume more current in order to reach the same power levels using a lower voltage according to the Power [P]= Current [I] * Voltage [U] equation. This curve won't be as steep using the LDO regulator I believe, as it has a constant drop-out voltage, making it more stable. But the DCDC regulator will be more power-efficient in most scenarios if I'm not mistaken. 

Best regards,

Simon