nRF 9160-DK i2c sleep current consumption

RE: nRF 9160-DK i2c sleep current consumption

kuchx — Thu, 08 Feb 2024 14:09:53 GMT

Hi Håkon,

Okay, thanks for the heads up. For now the VDD is good enough!

I did some investigation about why I saw the 370uA when sensor wasn't working and i2c should be suspended. Without digging deep in code my assumption is that if one of I2C line is pulled low (in my case when 5V was actually 0, both SDA and SCL was pulled low) the I2C peripheral wasn't actually suspended. The driver probably thinks that slave is pulling the line low so it can't suspend the peripheral when there is ongoing communication.

Anyway, this issue is solved now and hope this can help someone in future! Thanks for the assistance Håkon!

RE: nRF 9160-DK i2c sleep current consumption

helsing — Wed, 07 Feb 2024 14:53:07 GMT

Hi Andris,

Great that you found the cause. Thank you very much for posting the solution, this is helpful to others as the DK is flexible but complex.

5V comes directly from VBUS. If you short SB40 in the image below, the voltage will then bypass the diode, going back to 5V5. This will let the External supply net also go out to 5V on J1. (In case you are not using nRF9160 DK Revision 1.1.0: Double check the solder bridge number in the schematics as this potentially could vary from revision to revision.)

RE: nRF 9160-DK i2c sleep current consumption

kuchx — Mon, 05 Feb 2024 14:20:03 GMT

So I did some investigation and it turns out everything works okay. There were series of my own mistakes which led me to think that there is something wrong with HW.
First about the previous response. As I said, I tried to test I2C sleep without I2C lines connected to slave device - there was a bug in code and the i2c peripheral wasn't suspended, that is why I saw the same ~370uA.

About the original issue. The slave device was powered from nRF9160-DK (5V and GND on P1). It turns out that 5V is 0V when powered externally and I only noticed this when I connected Salae to SDA and SCL and did not understand why the lines are pulled low instead of high. I connected the + to VDD and now everything works as expected. I guess the slave device was draining SDA and SCL trying to source itself while on VIN there were no voltage.

It was my fault that I didn't check DK schematic were it is obvious that 5V is only available when USB is connected. Anyway, thank you for your help, the problem is solved now and I can move on with next steps!

RE: nRF 9160-DK i2c sleep current consumption

kuchx — Mon, 05 Feb 2024 07:26:09 GMT

Hi Håkon,

Thanks for the suggestions.

Indeed, I have external 10k pull-ups on SDA and SCL lines. As a quick test whether this issues is due to slave device or because of the pull-ups I just disconnected the I2C lines from the slave device and left the I2C driver running. Unfortunately I got the same result ~370uA when I2C should be suspended. So I guess the only option is to deep dive into the code and check the 1) suggestion you mentioned.

RE: nRF 9160-DK i2c sleep current consumption

helsing — Thu, 01 Feb 2024 21:21:19 GMT

[quote user=""]Now comes the question what is wrong with i2c, why I did not see any current drop when i2c is in sleep mode?[/quote]

Here are three thoughts to begin with:

1) It could be that a TWI clock request is not released. In that case one will have to look at the driver implementation.

2) Another cause could be the GPIO configuration, for example that there is a pull-up on some of the lines and that it is pulled down externally. In order to investigate this further you could read out the GPIO registers to see if everything is as expected(nrfjprog --memrd <address>). TWI typically has a pull-up on SDA and SCL, and perhaps this is removed when suspending. This could lead to floating lines and a target(slave) drawing excessive current.

3) A third scenario with high current consumption could be if the GPIOs are set to LOW in suspend, while at the same time there is an external pull-up. Current will then flow through the resistors.

RE: nRF 9160-DK i2c sleep current consumption

helsing — Tue, 30 Jan 2024 21:05:34 GMT

Hi Andris, thank you for the update. Just wanted to let you know we have started looking into this.

Regards,
Håkon

RE: nRF 9160-DK i2c sleep current consumption

kuchx — Mon, 29 Jan 2024 13:58:05 GMT

Oh I forgot to mention, I'm working in VS code with nRF SDK 2.5.0 version. "CONFIG_SERIAL=y" was left there after the UART low power test (during measurements on i2c I set it to 'n'), so when I measure ~370uA when i2c should be sleeping, the UART wasn't enabled