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LP-EM-CC2340R5: Reset issue because of the LFXT crystal

Vinayak Bhatiya
Prodigy 40 points
Part Number: LP-EM-CC2340R5

Tool/software:

Hello,

I am using the TI MCU "CC2340R52E0RKPR".

I faced an issue in which my MCU stuck at certain intervals at that time the watchdog is not implemented on my customized PCB.

After implementing the watchdog the MCU reset itself. But the things is sometimes it's reset via LFCLK and these i found on most of my customized PCB.

I am not using Crystal which is mentioned in your EVK because of the price constrained.

Crystal Part No.: MP05347 
Load capacitance: 7pF

So kindly suggest this problem is of the Crystal or other things.

Here I also attach a snapshot of my design

  • 0
    TI__Guru**** 169754 points

    Hi,

    If I understood your description correctly, you are experiencing MCU lockups independently of the watchdog state and when you enable the watchdog you mentioned the LFCLK is the source of the reset. Is this correct? 

    If so, are you reading the RTSSTA register (bitfield SYSSRC) to confirm if the cause of reset is indeed the LFCLK? Also, you mentioned that sometimes this is due to the LFCLK, but do you know what are the other reset causes? 

    How do you know the MCU is locked? Does it simply stop working, is it stuck in a forever loop or does it disconnect from JTAG? The first two scenarios can be software-related, but the second one is indicative of a POR reset.

    Reference: section 6.11.11 of the CC23xx Technical Reference Manual (SWCU193)

    One detail that caught my attention is the very low load capacitance on your LFXTAL - the two load capacitors are in series in relationship with the crystal, thus yielding just 3.5pF of load. To have a 7pF load capacitance you must use a series association such as two 14pF capacitors.

    Reference: section 3.3 of the Crystal Oscillator and Crystal Selection for the CC13xx, CC26xx, and CC23xx Family of Wireless MCUs (SWRA495)

    Hope this helps,

    Rafael

  • 0 in reply to desouza
    Prodigy 40 points

    Hello,

    desouza said:
    If I understood your description correctly, you are experiencing MCU lockups independently of the watchdog state and when you enable the watchdog you mentioned the LFCLK is the source of the reset. Is this correct? 

    No, sometimes the device is continuously reset due to the LFCLK on the startup (when we provide supply to the board) in some devices.

    desouza said:
    If so, are you reading the RTSSTA register (bitfield SYSSRC) to confirm if the cause of reset is indeed the LFCLK? Also, you mentioned that sometimes this is due to the LFCLK, but do you know what are the other reset causes? 


    As shown in the above figure, we are reading the reset reason using the above function and we get a reason as PMCTL_RESET_LFXT

    desouza said:
    How do you know the MCU is locked? Does it simply stop working, is it stuck in a forever loop or does it disconnect from JTAG? The first two scenarios can be software-related, but the second one is indicative of a POR reset.

    Device stops working and we detect it using a watchdog timer(i.e. Watchdog reset 20s)

  • 0 in reply to Vinayak Bhatiya
    TI__Guru**** 169754 points

    Hi,

    Thanks for the clarifications.

    Vinayak Bhatiya said:
    No, sometimes the device is continuously reset due to the LFCLK on the startup (when we provide supply to the board) in some devices.

    Did you change the load capacitors on the LFXTAL as I mentioned before? This low load capacitance can be the root cause of all the issues you are experiencing.

    Regards,

    Rafael

  • 0 in reply to desouza
    Prodigy 10 points

    Hi,

    I am changing the Load capacitor value to 12pF and it's working.

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