nRF52840 working voltage

[Sridharr]

nRF52840 works with 1.8V supply voltage? We are using Circuit configuration number.5. it tells VDD should connect to VDDH.

As per the circuit configuration 5: VDDH is N/A. We should worry only about VDD rail, as per spec it is 1.7–3.6 V. We are planning to operate with 1.8V. Do you foresee any issues?

 In case if we don’t want to use USB power/ interface as per configuration 5 , Can we leave VBUS pin open or connect it to GND. nRF52840 works only with VDD rail?

[Håkon]

The VDDH pin on the nRF52840 must either be supplied with a voltage within its valid range and no supply on VDD, or be shorted to VDD and be supplied with a voltage within VDD's valid range.
The Regulator operating conditions displays valid voltage ranges for VDD and VDDH.

It is OK to supply the nRF52840 on VDD, with VDDH shorted with VDD, at 1.8 Volts.
This is shown in e.g. reference circuit configuration no. 5 and 6.
The device will then be in normal mode as explained in Power supply chapter
There are no issues when doing this.

Circuit no. 5 has the USB peripheral enabled, hence the VBUS pin must be routed out to the USB connector and decoupled with a capacitor.
However circuit no. 6 does not use the UBS peripheral, and shows that the VBUS pin can be grounded to reduce the BOM if USB is not needed. 
I will advise you to follow the reference schematics as much as possible, but it is no problem mixing circuit no. 5 and 6 regarding USB. The main differences are the external circuitry needed to use the built in DC/DC-regulator DCDCEN1 and NFC.
It is OK to ground the VBUS pin if you are not going to use the USB peripheral.

The nRF52840 only needs to be supplied on VDD (shorted with VDDH)  to work.

Best regards,
Håkon

[Sridharr]

Thanks for your response.

nRF52840 power consumption same when we operate with 1.8V and 3.3V? 
When i simulate in the online Power profiler, i see 1.8V power consumption is 22% lesser than 3.3V with DC-DC regulator.
I believe the Power consumption should be same with in the operating voltage range. Can you please share any test date with 1.8V vs 3.3V power consumption?

We are operating with battery, even 10% of current consumption difference will have big impact on our product. What is your recommended operating voltage for low power consumption.

[Håkon]

Hi,

The power consumption will vary depending on supply voltage and usage, it will most likely not be equal when VDD is changed. The online power profiler is based upon characterization data for different use cases and voltages. 

I recommend having a look at this thread. 

A few comments:
The efficiency of the DCDC regulator increases as the current consumption rises.
When enabled, the DCDC regulator will draw some amount of current to operate, hence the gains of using DCDC vs LDO becomes less when the average current draw is decreased.
As mentioned in the linked thread, the device can be set up to switch to the regulator which gives the best overall power consumption based on current draw. 

When DCDC is enabled;
It is better to have the VDD supply voltage low, e.g. 1v8, to optimize for energy
It is better to have the VDD supply voltage higher, e.g. 3v3, to optimize for current consumption
Ideally a battery with low voltage and high number of mAh would be good, but this can be expensive and can take more space.

You can play around more with the power profiler to see what makes sense for your use case, e.g. connection interval, slave latency, etc. You can see that when the radio activity happens less frequently the difference in average current consumption between 1v8 and 3v3 becomes less -  it could be better to have a lower VDD due to much sleep time.
For a high frequency in radio activity the difference in average current increases - it can be better to have a higher voltage battery to reduce current.