SAADC VDDHDIV5 input on nRF52840 rev. 1

RE: SAADC VDDHDIV5 input on nRF52840 rev. 1

Karl Ylvisaker — Mon, 05 Dec 2022 13:20:09 GMT

Hello,

I am glad to hear that you found the answers here useful! :)

It is indeed not explicitly mentioned in the datasheet - I will write a note about this to our techwriters and see if it is something they can amend if there is a future release of the Product Specification planned.

Thank you for the feedback, we appreciate it! :)

Best regards,
Karl

RE: SAADC VDDHDIV5 input on nRF52840 rev. 1

pmochocki — Fri, 02 Dec 2022 22:25:48 GMT

[quote userid="87869" url="~/f/nordic-q-a/80778/saadc-vddhdiv5-input-on-nrf52840-rev-1/336250"]Yes, from what I can tell VDDH is not really in use when the nRF is in Normal voltage mode, so I do not think it is a valid source to measure the nRF's supply voltage when not in high voltage mode.[/quote]

This is very useful and has helped me a lot, as I was wondering why I get strange results when using VDDHDIV5 in Normal voltage mode. To bad that this information is not in the datasheet. I understand that VDDH is not really in use when the nRF is in Normal voltage mode, but VDDH is connected to VDD so users might expect this to work.

RE: SAADC VDDHDIV5 input on nRF52840 rev. 1

Karl Ylvisaker — Thu, 28 Oct 2021 10:57:28 GMT

Hello again Norbert,

[quote user="ngrunert"]C19 next to the chip.[/quote]

Thank you for confirming this.

[quote user="ngrunert"]Sounds good. I am interested to hear their comments, if any.[/quote]

The DK developers just got back to me, they too concluded that this must then be caused by something internal to the SoC when operating in normal voltage mode contra high voltage mode. They conclude that this must be the case since you are measuring 3 V on C19.

[quote user="ngrunert"]Okay. My experiment was for the next board architecture. I was not aware of any dependency between SAADC input and power configuration (in hindsight it is obvious, though).[/quote][quote user="ngrunert"]With 3.0V supplied to P27 and SW9 in LiPo position, I get a reading of 170 (=3.0V) too. So indeed VDDHDIV5 is invalid if not in HV power configuration. That is totally OK for me.[/quote]

Great, I am glad to hear that you too are seeing the expected measurements in the High voltage configuration, and that this is not an issue for your next project.

[quote user="ngrunert"]Thanks for your time,[/quote]

It is no problem at all, Norbert - I am happy to help!

Please do not hesitate to open another ticket if you should encounter any other issues or questions in the future.

Good luck with your development!

Best regards,
Karl

RE: SAADC VDDHDIV5 input on nRF52840 rev. 1

Norbert — Thu, 28 Oct 2021 07:54:34 GMT

Hello Karl,

[quote userid="87869" url="~/f/nordic-q-a/80778/saadc-vddhdiv5-input-on-nrf52840-rev-1/336250#336250"]reach out to the developers of the nRF52840 DK to see if they have any additional comment on this[/quote]

Sounds good. I am interested to hear their comments, if any.

[quote userid="87869" url="~/f/nordic-q-a/80778/saadc-vddhdiv5-input-on-nrf52840-rev-1/336250#336250"]Could you specify where you accessed VDD_HV on the board[/quote]

C19 next to the chip.

[quote userid="87869" url="~/f/nordic-q-a/80778/saadc-vddhdiv5-input-on-nrf52840-rev-1/336250#336250"]Could you also try to switch the SW9 to Li-Po, provide 3 V to the J6 or P27 port, and then see what your results for the VDDHDIV5 measurements are?
[/quote]

With 3.0V supplied to P27 and SW9 in LiPo position, I get a reading of 170 (=3.0V) too. So indeed VDDHDIV5 is invalid if not in HV power configuration. That is totally OK for me.

[quote userid="87869" url="~/f/nordic-q-a/80778/saadc-vddhdiv5-input-on-nrf52840-rev-1/336250#336250"]However, if you are not using the nRF in high voltage mode you should just use the SAADC's _VDD input instead of the VDDH to measure the voltage of the supply.
[/quote]

Okay. My experiment was for the next board architecture. I was not aware of any dependency between SAADC input and power configuration (in hindsight it is obvious, though).

Thanks for your time,

Norbert

RE: SAADC VDDHDIV5 input on nRF52840 rev. 1

Karl Ylvisaker — Wed, 27 Oct 2021 14:12:47 GMT

Hello Norbert,

[quote user="ngrunert"]Sorry for closing the thread before.[/quote]

No problem at all - the feature is intended to summarize tickets by highlighting the answer that solved the issue, but it also locks the thread to avoid that it later diverges from the original issue.

[quote user="ngrunert"]

Back to the topic: In my understanding, with SW9 in position "VDD", VDD_nRF is about equal to VDD_HV, so the measurement should work. I checked the VDD_HV level and it is ~3.0V, same as VDD_nRF (there is only an load switch between the two).

Am I wrong here?

[/quote]

Yes, from what I can tell VDDH is not really in use when the nRF is in Normal voltage mode, so I do not think it is a valid source to measure the nRF's supply voltage when not in high voltage mode. I will reach out to the developers of the nRF52840 DK to see if they have any additional comment on this.

Could you specify where you accessed VDD_HV on the board when you measured it?
Could you also try to switch the SW9 to Li-Po, provide 3 V to the J6 or P27 port, and then see what your results for the VDDHDIV5 measurements are?

However, if you are not using the nRF in high voltage mode you should just use the SAADC's _VDD input instead of the VDDH to measure the voltage of the supply.

Best regards,
Karl

RE: SAADC VDDHDIV5 input on nRF52840 rev. 1

Norbert — Tue, 26 Oct 2021 15:22:28 GMT

Hi Karl,

Sorry for closing the thread before.

Am I wrong here?

Thanks,

Norbert

RE: SAADC VDDHDIV5 input on nRF52840 rev. 1

Karl Ylvisaker — Tue, 26 Oct 2021 13:37:31 GMT

[quote user="ngrunert"]No, as I said earlier, SW9 is in middle position (VDD). The power is coming from the USB I/F.[/quote]

Yes, but as mentioned this will not supply the device through VDDH, which means that your SAADC's measurement of the VDDHDIV5 might be correct even still. If you wish to supply the device through the VDDH pin you will need to have the nRF52840 in High Voltage mode, which can be achieved by switching the SW9 to Li-po. In this case you will have to supply the nRF through the J6 or P27 port.

Best regards,
Karl

RE: SAADC VDDHDIV5 input on nRF52840 rev. 1

Norbert — Tue, 26 Oct 2021 12:55:30 GMT

[quote userid="87869" url="~/f/nordic-q-a/80778/saadc-vddhdiv5-input-on-nrf52840-rev-1/335961#335961"]Could you confirm that you tested this with the SW9 switch in the Li-Po position, while powering the device with 3.0 V through the J6 or P27 port?[/quote]

No, as I said earlier, SW9 is in middle position (VDD). The power is coming from the USB I/F.

Thanks,

Norbert

RE: SAADC VDDHDIV5 input on nRF52840 rev. 1

Karl Ylvisaker — Tue, 26 Oct 2021 12:25:25 GMT

Hello Norbert,

[quote user="ngrunert"]I also found a third V1.0.0 DK which behaves exactly like my other two boards.[/quote]

Could you confirm that you tested this with the SW9 switch in the Li-Po position, while powering the device with 3.0 V through the J6 or P27 port?

[quote user="ngrunert"]I am completely at a loss here. Would you please do me a favor and check the markings of the chip on your V1.0.0 DK, just to make sure you have a legit DK and not an upgraded version?[/quote]

Sure thing - I just checked my board, and I do indeed have a AAC0 version of the chip.

Best regards,
Karl

RE: SAADC VDDHDIV5 input on nRF52840 rev. 1

Norbert — Mon, 25 Oct 2021 15:06:52 GMT

Hello Karl,

I checked once more the boards and still got the same results. The board's HW looks fine. I also found a third V1.0.0 DK which behaves exactly like my other two boards. Then, I used bare-metal programming to configure and read the SAADC, totally avoiding the SDK. Still the same results.

I am completely at a loss here. Would you please do me a favor and check the markings of the chip on your V1.0.0 DK, just to make sure you have a legit DK and not an upgraded version? It should read 'AC0'. Alternatively, you could also read FICR->INFO.VARIANT which should give 0x41414330 (= "AAC0").

If you find that your chip is really a rev. 1, I suggest to give up and file it under great unresolved mysteries of the universe.

Thanks,

Norbert

RE: SAADC VDDHDIV5 input on nRF52840 rev. 1

Karl Ylvisaker — Sun, 24 Oct 2021 01:30:22 GMT

Hello again, Norbert

[quote user="ngrunert"]Power supply is USB. SW9 is in middle position (VDD power), the coin cell battery removed. The 3V are generated on-board from the buck regulator.[/quote]

Oh, it seems I have misunderstood your configuration earlier.
I did my measurements with a supply of 3V directly on the VDDH input - with the SW9 switch set to Li-Po, for High Voltage mode. If the SW9 is in the VDD position the nRF52840 will enter Normal voltage mode as opposed to high-voltage mode. In normal voltage mode you should not use the VDDHDIV5 to measure your VDD bus voltage, but instead use the _VDD input directly. In your test, do you see the expected SAADC measurements if you configure the SAADC to measure _VDD instead of _VDDHDIV5 (while keeping SW9 in the VDD position)?

For all the details about the DK's power supply circuitry you could download the nRF52840 DK's schematics here, to take a closer look.
Fair warning, the power circuitry of the DK is not the easiest to familiarize with due to the array of power switches utilized for the different configurations.

Best regards,
Karl

RE: SAADC VDDHDIV5 input on nRF52840 rev. 1

Norbert — Fri, 22 Oct 2021 16:30:22 GMT

Hello Karl,

Thanks for the feedback. Very strange, indeed. I just reran the experiment with the same settings you have and still get only around 136 (2.39V).

Power supply is USB. SW9 is in middle position (VDD power), the coin cell battery removed. The 3V are generated on-board from the buck regulator.

The board should be unmodified, though it is not in a pristine condition. Chip version is Q1AAC0.

I will dig further on Monday and let you know.

Thanks for your help,

Norbert

RE: SAADC VDDHDIV5 input on nRF52840 rev. 1

Karl Ylvisaker — Fri, 22 Oct 2021 14:27:44 GMT

Hello again, Norbert

I just tested this on my end, and using the default SAADC init and channel config (same as the SAADC example, only changing the _AIN0 to _VDDHDIV5), I am seeing both the nRF52840 v1.0.0 and v2.0.1 output the raw integer value 170 (with a few LSB fluctuation) when powered by a steady 3 V through the VDDH.
This corresponds to ~2.98 V, which is what I would have expected..

I find it very strange that you are seeing this consistently on two different v1.0.0 boards though. Have you made any modifications to these boards? Could you also elaborate on your board configuration (switch positions) and which port you supply the 3 V on when you conducted these tests?

Best regards,
Karl

RE: SAADC VDDHDIV5 input on nRF52840 rev. 1

Norbert — Thu, 21 Oct 2021 13:48:17 GMT

Hi Karl,

Thanks a lot for confirming.

I am very curious to see the result of your investigation. This outcome will impact our next design.

Best regards,

Norbert

RE: SAADC VDDHDIV5 input on nRF52840 rev. 1

Karl Ylvisaker — Thu, 21 Oct 2021 13:34:21 GMT

Hello again, Norbert

Thank you for your patience with this.

[quote user="ngrunert"]

VDDHDIV5 should provide 3.0V/5 = 0.6V at the input of the gain stage (ref. to PS1.5, fig. 148), so according to the PS this is fine.

Where do you see that the input range is limited to 2* 1.2V? The link you provided says the same thing as the PS, i.e. that AINx have to be between VSS and VDD (up to 3V, here). The input of the SAADC code after the gain stage should not be larger as VREF (0.6V), else the value is clipped.

[/quote][quote user="ngrunert"]To the best of my knowledge, the saadc example does not enable DCDC0. It does not make much sense on the DK as VDDH = VDD = 3.0V by the DK's HW architecture.[/quote]

Ah, yes of course, you are completely right. The DCDC is also indeed not enabled by default in the examples.
The input range will still be limited by the chosen gain and reference, but it does indeed not matter for this case since you are measuring on VDDHDIV5.

[quote user="ngrunert"]Yes. VDDH is rock stable at 2.98V.[/quote]

Thank you for confirming this. I assumed that you already knew, but from experience I still had to ask.

[quote user="ngrunert"]The result is the measured voltage, not the raw integer value from the SAADC.So factoring in the changed gain stage, the result if the same.[/quote]

Right, I was under the impression that you were talking about the raw integer value, which definitely would have been strange if it had been the case.

I do not immediately see any good explanation for this behavior.
I will try to replicate this behavior at my end tomorrow, I will update you as soon as I have got something.

Best regards,
Karl

RE: SAADC VDDHDIV5 input on nRF52840 rev. 1

Norbert — Mon, 18 Oct 2021 13:11:00 GMT

Hi Karl,

[quote userid="87869" url="~/f/nordic-q-a/80778/saadc-vddhdiv5-input-on-nrf52840-rev-1/334607#334607"]Changing the gain to 1/2 will affect your input range - with this configuration you should really only be able to measure values between 0 - 1.2 V. [/quote]

VDDHDIV5 should provide 3.0V/5 = 0.6V at the input of the gain stage (ref. to PS1.5, fig. 148), so according to the PS this is fine.

[quote userid="87869" url="~/f/nordic-q-a/80778/saadc-vddhdiv5-input-on-nrf52840-rev-1/334607#334607"]That sounds strange to me. Are you getting the same output regardless of gain stage?[/quote]

The result is the measured voltage, not the raw integer value from the SAADC.So factoring in the changed gain stage, the result if the same.

[quote userid="87869" url="~/f/nordic-q-a/80778/saadc-vddhdiv5-input-on-nrf52840-rev-1/334607#334607"]Could you share with me the code you are running when this happens?[/quote]

As I said, it is the SDK 17.1.0 saadc example with the modifications in the original post (main.c, line 153). No other modifications.

[quote userid="87869" url="~/f/nordic-q-a/80778/saadc-vddhdiv5-input-on-nrf52840-rev-1/334607#334607"]Could you try this again with the DCDC disabled, to see if it makes any difference to the values you are measuring?[/quote]

To the best of my knowledge, the saadc example does not enable DCDC0. It does not make much sense on the DK as VDDH = VDD = 3.0V by the DK's HW architecture.

[quote userid="87869" url="~/f/nordic-q-a/80778/saadc-vddhdiv5-input-on-nrf52840-rev-1/334607#334607"]Do you have any possibility of externally measuring or scoping the VDDH of the devices, such as through an oscilloscope? [/quote]

Yes. VDDH is rock stable at 2.98V.

Best regards,

Norbert

RE: SAADC VDDHDIV5 input on nRF52840 rev. 1

Karl Ylvisaker — Mon, 18 Oct 2021 12:33:06 GMT

Hello Norbert,

[quote user=""]I chose to increase the input voltage swing on the ADC by configuring the gain stage from 1/6 to 1/2. This should normally give better results.[/quote]

Changing the gain to 1/2 will affect your input range - with this configuration you should really only be able to measure values between 0 - 1.2 V.

[quote user=""]I got the same result with the gain stage set to 1/6. The result is consistent across the two boards.[/quote]

That sounds strange to me. Are you getting the same output regardless of gain stage?
Could you share with me the code you are running when this happens?

Do you have any possibility of externally measuring or scoping the VDDH of the devices, such as through an oscilloscope? It would be very helpful to know what the voltage on VDDH is for reference during the measurements.

[quote user=""]I can only guess that this behaviour (if confirmed) is a side-effect of erratum 197.[/quote]

Could you try this again with the DCDC disabled, to see if it makes any difference to the values you are measuring?

Best regards,
Karl