Hello,
I have been developing and using the nRF9e5 for 7 years and we recently want to try to deploy the device at temperatures of -20oC and below. The code is fixed and has been operating in ambient conditions for around 6 years.
I am using the reference layout design, and have uprated all the passive components in terms of tolerences and replaced the XTAL with a TSX-3225 16.0000MF18X-AC3 (www.eea.epson.com/.../1705581.PDF) so everything is within spec (power source for testing is a uk.rs-online.com/.../).
The operation of the device is to transmit 16 bytes then go into lower power mode for x seconds, then powerup RX to listen for a carrier, if none, go to TX and send the same 16 bytes, if carrier recieve data and modify the 16 byte packet to TX.
After 256 loops of power down and transmission the data transmitted returns to a defualt value if no carrier seen.
The problem is that some of the identical devices, (same batch build, same reel of nRF9e5, same reel of EEPROM) continue to work for hours, in fact 3 devices have been working for 8 weeks and others only last minutes at a temperature of -25oC.
I have tested with a powered constant carrier signal to ensure that the transmission frequency is not moving off channel and the power level is constant, on a nRFe95 that doesn't exhibit this this shutdown issue and it is perfect.
I am currently using CK_CNT of 0x02 in order to use the higher accurate XTAL for timing purposes in the low power RTC wakeup, generaly we use 0x04 for maximum power saving, but this gives no xtal visibility of course.
When the nrf9e5 exhibits the problem of no transmission in the lower temperature I am able to quickly remove the device and test to see if the XTAL is running which it is, then after a few seconds of being in ambient conditions the tag restores transmission correctly.
Interestingly the 256 loop iteration timing seems to be accurate, so for 2 seconds of power down x 256 in a loop with a transmission in all of them, before returning to a default condition, the timing seems ok.
So my conclusion currently is that the transceiver section is not functioning at lower temperatures, and the 8051 is, with a spread of tolerance chip by chip on what the lowest functioning temperature is.
I will try placing some GPIO level changes in the code as a rough means of tracking operation, eg if no transmission I will still be able to check 8051 operation.
Edit: Ok I have put in I/O and I can see the nrf9e5 (8051 element) is still running exactly as normal but I see no TX. The TX code is definitely running. The nRF9e5 can also recieve data without issue as by sending it data when no TX is observed in the low temperture, the 16 byte string is modified to the correct string when the first TX is received after returning it to ambient conditions.
So I am narrowing the focus down to the TX subsystem.
Any assistance on this manner I would be extremely grateful to help narrow the testing.
