nRF52840 I2C Stops Working

[Mark J]

Hi,

I have been using I2C code for almost a year to talk to a variety of sensors with complete success. Typically, we have used a Nordic BL654 module that includes an nRF52840. Recently we replaced this module with a nRF52840 chip. I2C and other usage remained identical. We built 30 boards. On approx 5 of these boards, I2C worked and then stopped working. Sometimes a power cycle recovers I2C support for a while before it fails again and sometimes it does not (I2C stays broken). Putting a scope on the SCL and SDA pins shows DC 300 mV and 3.3 Vdc on each of these pins respectively when I cycle through I2C reads and writes that work on other boards just fine. In code, TWI timeouts occur. My hardware engineer suggests that the chip is the issue. Note that it still runs code and its other interfaces seem to work fine. 

Also important - we purchased the 52840 chips through the grey market. Welcome to 2022.... sigh. I have included a pic showing the chip numbers below:

Could this chip be an eng sample or pre-release on which this kind of issue may be expected? Is there any version of the 52840 that exhibited this kind of behavior?

Thanks in advance.

Regards,

Mark J

[Simonr]

Hi

You've got a point there, seems very strange. Does your application use the LF crystal or internal LFRC during operation? It could be that your application is running on the edge of what the clock can handle, so that the 5 malfunctioning ones started drifting after a while? Could you provide some details on what the application is doing so we might get a better understanding as to what could cause this. From what I can tell, there shouldn't be anything wrong with the I2C on these chips, but if you suspect the chip you can fill in the attached CFR document so QA can process your request.

Best regards,

Simon

7180.CustomerFailureReport.docx

[Mark J]

Hi Simonr,

Our product uses ext 32.768 kHz and 32 MHz crystals. No LF.

The application is a ventilation sensor. We measure C02 in air for covid ventilation effectiveness measure. We are idle for min or hours and then a clock inits and uses I2C to talk to a CO2 sensor chip. Then, it deinits and goes back to idle. When we see a fail we see it right after device start and again after each I2C comm attempt (to the sensor chip). I will review the CFR doc.

Thanks, 

Mark J