troubleshooting of produced prototype: nrf9160

[David]

Hello,

I have developed 10pcs of one prototype with the nrf9160 SiP. 

I have some questions regarding some errors im having.

Regarding the SIM 1V8 driver VCC, for UICC interface, I am observing a fluctuation on this channel/voltage, from 0V -> 0.4 VDC, with approximately 1hz frequency.

What can cause this to happend, what is the normal behaviour of this channel when it is short-circuited with ground or something else/similar ?

My second question is regarding the attached image, im observing this on a few of my prototypes, im not able to upload any modem firmware to the SiP, any idea why?

Regards,

David

[David]

Hello,

I've managed to get the prototype working with my application, when following this tutorial 

https://devzone.nordicsemi.com/nordic/cellular-iot-guides/b/getting-started-cellular/posts/nrf-connect-sdk-tutorial.

Therefore, I now have to solve the sim-interface issue on my prototype.

I only had 10uF ceramics laying around, so I added 4 for IO_supplyu/DEC0.

If I cut the 1V8 sim vdd trace, which goes to the analoge switch, I still can measure the same fluctuation on this voltage, when measuring between "gnd / analoge switch pin 14".

I can even measure it on the analoge switch VCC input "pin 14", even if it is not connedted to the 1V8 sim vdd from nrf9160 SiP.

I have checked the close-by traces for this analoge switch, and these are (SIM_IO, SIM_CLK, SIM_RST).

See attached pictures below, for visual.

What can be causing this ?, I think it can have something to do with the SIM_IO, SIM_CLK, SIM_RST lines?

At what circumstances does the sim-interface behave this way?

Regards, David