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]

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

[David]

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

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

[David]

Hello again,

I must correct myself: 

David said:

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

J7 was set to ground.

Thank you for replying so fast, It seems that the main issue now, is the missing 1V8 voltage from the SIM vdd.

I would appreciate it, if your support team could answer me on, what possily  can cause this, maybe firmware related?

Regards, David

[Andreas]

Hi,

 

OK, thanks for correcting.

 

I am a 'HW guy' so not really the right person to judge your FW or the modem FW, but as Didrik judged it we believe this to be HW related.

 

Best regards,

Andreas