nRF9160 power supply selection

RE: nRF9160 power supply selection

tedhavelka — Wed, 20 Apr 2022 20:22:34 GMT

Good evening Kenneth,

Thanks for the further help. I have just created a new ticket 87158 for nRF9160 low power and Zephyr CONFIG_PM=y questions.

Thank you especially for the pointer to the hardware files. It must be me, that I've had some trouble locating the schematics files for various Nordic Semi development kits. I don't know that they are too buried, but I believe developers would benefit from having a more direct link or search result pointing to them.

On a Devzone use note, I don't yet fully know the normal "ticket life" flow, though in previous tickets I have on a few occasions asked Nordic Team to change a given ticket status to "closed" or "answered" once the issue is resolved.

For now I would like to keep this ticket open. I'm hoping to find answers to these questions. Once answered I will make a final reply here, pointing to the answers (documentation or other Devzone posts), and request to close this ticket then, if that is alright.

Thank you again for your help Kenneth. Stay safe,

- Ted

RE: nRF9160 power supply selection

Kenneth — Wed, 20 Apr 2022 08:52:22 GMT

1.) Hardware files are public yes, you can find them at the bottom of this page:
https://www.nordicsemi.com/Products/Development-hardware/Nordic-Thingy-91/Download?lang=en#infotabs

2-3.) I suggest to make a new case for these questions, the person that typically handle specific current consumption realted question are out of office this week though. Or you can reply to this case and I can leave this case open and assign this case to him when he is back next week.

My comments in general are:

From here I can find the floor current is 2.7uA:
https://devzone.nordicsemi.com/power/w/opp/3/online-power-profiler-for-lte

This is slightly higher than the typical value I(MCUON1):
https://infocenter.nordicsemi.com/topic/ps_nrf9160/_tmp/alta.nRF9160/autodita/CURRENT/parameters.id_current_sleep.html

In the nRF Connect Power optimzation documentation I can find it's stated 4uA:
https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/app_power_opt.html#

So you should expect the current consumption is around ~3-4uA yes, if you measure ~22uA it is is likely an internal peripheral (e.g. gpiote) that may be drawing the current or there is some external circuitry that is drawing current.

Kenneth

RE: nRF9160 power supply selection

tedhavelka — Tue, 19 Apr 2022 18:33:52 GMT

Hello Kenneth,

Thank you for the fast reply, and patience with a basic hardware question. I have read Nordic's on-line Power Profiler description and notes on limitations a few times now. Repetition helps cement understanding. I understood the absence of full peak current reporting. Thanks however for the "sanity check" reminder on the obvious point "voltage drop too great running LTE modem and SiP direct from high impedance battery".

Regarding Nordic's Thingy91, my team's hardware lead has designed a custom board for our battery based product idea, and his design follows the patterns of the Thingy91 in many respects. The boards are not identical but they are similar.

So last summer 2021 I had read much of Thingy91 documentation on-line. Lots of good information on your site! One thing I could not find, however, is a schematic of the Thingy91.

Question (1) Is Thingy91 schematic not publicly available?

We have on hand one nRF9160DK board, version 1.0.0 as silk-screened on the back of this board. With a modified "hello_world" app from another ticket I started here in 2022 March we can measure a floor current of 4.5uA used by the nRF9160 SiP. On a custom board I can reach a floor current of ~22uA. I don't have test points which permit me to measure exclusively SiP current. Practically, however, I need to reduce the total board current to single microamps current use, in deep sleep mode, in order to justify use of the nRF9160 in our design.

Question (2) does the nRF9160 SICA B1A version of this SiP no longer have an internal leak current issue when VDD_GPIO is supplied with 1.8 volts rail?

One concern I have is that I find floor current increase when I set just a subset (four GPIOs) to Zephyr's GPIO_DISCONNECTED pin config value in firmware. I may be opening a separate ticket if I cannot find a root cause for this. From another recent post 86752 I made one of your team confirms that Zephyr's DISCONNECTED configuration is the highest impedance way to configure a GPIO. So it is unclear to me how nRF9160 pins would turn on in some default setting that draws less current than when they are explicitly configured to be disconnected.

Final comment regarding my team's low power search efforts: to reach a floor current of 22uA with nRF9160 in our custom board I needed to disable Zephyr 2.6.0's power management feature, that is, to set CONFIG_PM=n. This feature increases floor current by about 25uA. I have some Zephyr source tree code to review, and perhaps this is best in a new ticket. In any case,

Question (3) Is it known that Zephyr 2.6.0 run time power management Kconfig feature steadily increases nRF9160 floor current?

Thank you for your help, Kenneth. You and your fellow engineers make this an excellent support forum!

- Ted

RE: nRF9160 power supply selection

Kenneth — Tue, 19 Apr 2022 12:10:45 GMT

Hi Ted,

Not sure if this answers your question directly, but below the https://devzone.nordicsemi.com/power/w/opp/3/online-power-profiler-for-lte you can find the comment:

"The tool does not show peak currents. The different bars in the graph show the average current within a specified event type, e.g. iDRX event. The radio RX/TX will typically give the highest peak currents, but it is only a small part of the event itself, hence the average current will be lower than the peak current. Please refer to the nRF91 Product Specification for expected min/max values for the different current components."

So the actual peak currents are even higher than shown, and they are the highest when the modem is used (highest peak is 435mA):
https://infocenter.nordicsemi.com/topic/ps_nrf9160/_tmp/alta.nRF9160/autodita/CURRENT/parameters.id_current_modem.html

So, based on this I can answer your question:

[quote user=""]Is my understanding here accurate? Would all bets for stable nRF9160 operation be off, if I power the SiP directly from a high impedance battery, one whose discharge curve is relatively flat among different battery type discharge curves?[/quote]

You can't make a design with a high impedance battery no, the voltage drop would be way too high. You might get some useful tips from the thingy91 design in terms of design:
https://www.nordicsemi.com/Products/Development-hardware/Nordic-Thingy-91

Best regards,
Kenneth