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  • Case ID: 304995
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nRF9160 not outputting 1.8V in "SIM_1V8" pin

KN7702

We have designed a custom board using the nRF9160. Most of the circuitry around nRF9160 is referencing the same as circuitry on the nRF9160 DK board. Upon flashing the modem firmware and the AT_Client sample application (with Bootloader), it seems that pin SIM_1V8 does not output 1.8V at all. 

I have noticed we have SIM_DET routed to our Sim Card Tray switch for switching between eSIM and SIM, but I have cut the trace since. The SIM_DET is now floating. 

The nRF9160 is powered from a 3.3V source and the ENABLE pin is at 3.3V (nRESET is also pulled high to 3.3V) and I can flash it with the Segger J-Link programmer, but the internal 1.8V regulator seems to be not operational. 

I understand there was a similar ticket before and it was resolved by reflowing the board. I could understand one or two boards might have reflow issue, but I have all of the boards exhibiting the same issue. 

Any help would be appreciated. 

  • 0 in reply to Håkon Alseth

    For what it is worth: we finally nailed down the issue. The devices we bought has a date code 2226 and a modem fw version 1.1.6 pre-programmed

    at AT+GCMR
    mfw-pti_nrf9160_1.1.6
    Updating the modem firmware to a version in line with our current SDK version fixed the issue. I guess the modem now gets the command sequence it expects to power on the SIM interface.
    Pascal
  • 0

    To follow up on this issue, I have identified that there was an assembly issue with the Sim Card Tray. The 1.8V pin is shorted to the Sim Card shield and that shorted to ground. 

    Since then, I have had those boards reworked. 

    Now, when I enabled the LTE modem by issuing AT+CFUN=1, I can measured 1.8V comes up momentarily (it stays at 1.8V for a second or so), then it goes down to 0V. This cycles every few seconds. The nRF9160 keeps on turning on 1.8V and then turning off afterward. 

    I used AT%XSIM=1 to initialize the SIM, it response with OK, but when I check using AT%XSIM? and it returns 0. It does not provide any cause either. 

    Could the SIM data signal is corrupted? 

  • 0 in reply to KN7702

    Hi,

     

    KN7702 said:
    Now, when I enabled the LTE modem by issuing AT+CFUN=1, I can measured 1.8V comes up momentarily (it stays at 1.8V for a second or so), then it goes down to 0V. This cycles every few seconds. The nRF9160 keeps on turning on 1.8V and then turning off afterward. 

    It is expected that the voltage to the SIM will be on only when communication towards the SIM is required.

    Have you checked your PCB traces from the nRF to the SIM to see if they're routed correctly? Is there any modules that can successfully communicate with the SIM card?

     

    Kind regards,

    Håkon

  • 0 in reply to Håkon Alseth

    So I have tried just enabling the Sim Card by sending AT+CFUN=41 (we are only LTE-M). This initiates the Sim Card correctly (1.8V is stabled) and I can read the IMSI and ICCID from it. In that sense, the 1.8V output from nRF9160 is indeed resolved. 

    I believe there is a much deeper issue related to design when initialize it using AT+CFUN=1. I will create a private ticket and review the schematic/layout. 

  • 0 in reply to KN7702

    The SIM initialization should be reported back regardless of the capabilities the SIM has with a given network. I am glad to hear that it worked out in the end, but your explanation indicates that the physical connection is unstable from nRF to the SIM itself. Be sure to check which modem fw is on your specific nRF9160 board, and update if it is older.

     

    Kind regards,

    Håkon

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