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

[Andreas]

Hi,

 

David said:

If I meassure the voltage on some other boards of my prototype, I meassure a stable 2.2V on DEC0, on the one prototype that I am having the issue with the sim-interface voltage, I meassure here between 2.1 and 2.2 VDC, oscillation. 

 OK, nice to know although I am not sure this answers anything at this point.

 

 

David said:

I am still waiting for the correct capacitor components, for DEC0 -> GND. Therefore, DEC0 is floating at the moment.

 Not sure if this is ideal, 4.7µF is better than nothing I would assume. It is not necessarily incorrect, but with 47µF the clock signals will be more resilient across PVT variation and is recommended for mass production devices.

 

 

David said:

I measure 0 Ohm between sim traces and gnd, when board is power off. Is this normal?

 Not sure, I have forwarded it internally.

 

 

David said:

You are correct, I am using an external strap between (pin 2 of J7 -> C24 pad 1 (capacitor below analoge switch)) 

 Thanks for the confirmation, this is all good then.

 

Best regards,

Andreas