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Original question:

CC2530: 32768Hz Oscillator Problem

CC2530: Urgent: Oscillator Problem with 32.768KHz Clock

amir mirbagheri
Prodigy 120 points

Part Number: CC2530
Other Parts Discussed in Thread: MSP430G2553, ,

Hi everyone,

I want to follow up with this thread that I opened couple of months ago.

In my design, I used two micro controller MSP430G2553 and CC2530. The two micro controller share the same 32768  Hz iscilllator.

The MSP430 has its own 32768 Hz oscillator using two 15pf capacitors and a  32768Hz crystal. The crystal P/N is ECS-.327-12.5-13FLX-C and oscilator circuit is pretty simple and according to MSP430G2553 datasheet.

Then I  output the oscilator signal on P1.0 pin (ACLK signal out). It is a square waveform with 0 and VDD voltage levels.I feed this signal to P2.3XOSC32K-Q2 according to TI application note SWRA409A.

Here is the link to this note: https://www.ti.com/lit/an/swra409a/swra409a.pdf?ts=1651109909216

this application note is based on CC254X series that use Bluetooth radio while CC2530 in my project uses Zigbee radio. I assume the two mico controllers are identical and only the RF radio part is different.  

Please let me know if it is OK to use the same circuit for CC2530 as well.

I tested couple of the final products for at least one week and all of them worked fine. I even performed temp cycle on them from -25C to +50C to make sure they are working at different termperatures

But unfortunately, one of them stop working just two or three hours after it was deployed on a bridge. It seems the 32768Hz oscillator stopped working. 

We have also many products that uses CC2530 with crystal oscillator that is similar to the CC2530 manual (two load capaciors + 32768Hz crystal) but some of them also have had the same problem and oscilator stopped working after some times and that is one of the reasons we decided to use an external clock source. 

My circuit design is exactly according to  SWRA409A. (External square clock with 0 and VDD levels). Do you have any idea what is the reason of stop working?

I checked the manual of CC2530 but I could not find any material regarding using an external source for 32768Hz oscilator . Please let me know if it is OK to use external clock?

As I mentioned, we had this problem even with the common recommended oscilator design (two 15pf capacior +crystal P/N:ECS-.327-12.5-13FLX-C), do you have any recommendation for solving this problem?

Thanks,

  • 0
    TI__Guru**** 171519 points

    Hi,

    amir mirbagheri said:
    Do you have any idea what is the reason of stop working?

    Since your system is running for some time, it becomes quite difficult to pinpoint an exact root cause, especially since there are two processors involved (the MSP430 and the CC2530). In this case I can only provide a few tips:

    - in your description it is unclear if the 32kHz signal is still being generated by the MSP430 - can you verify this? This would be the first step to isolate the root cause. 

    - The failed system is deployed but failed after a few hours. Since the deployed system might be subjected to different environmental conditions (high or low temperature, vibration, humidity), perhaps evaluating your product under these conditions (in a thermal chamber, for example) would be another step to isolate the problem.

    - If this issue affects only one device/board, perhaps you could try to replace it with another unit and see if it works?

    I will try to think about additional details that may help further debug this and reply back in case I find anything relevant.

    Hope this helps,

    Rafael

  • 0 in reply to desouza
    Prodigy 120 points

    Hi Rafael

    Thank you for your answer.

    The 32KHz signal is still being generated by MSP430 and then it is feed to CC2530 oscilator input.

    Unfortunately, we do not have access to the failed system right now. I do know that having access to it would be a great help in troubleshooting and we wiill try to access it at the earliest time.

    We always perform a temperatrure cycle from -25C to +50C on all of our products to make sure they can work reliably in different temperatures.

    At the deployment time the temperature was around 15C and at least for the time it was working, there was no significant temperature change. 

    The system is inside a box with IP67 protection and typically, water and moisture should not leak inside.

    We deployed two of these system just as a pilot and test. (this design is still in prototying steps and has not been deployed in large scale) and unfortunately both of them had problems after sometimes.

    Since we have had this 32KHz oscilator problem even with simpler designs (without MSP430. Only CC2530) My main question is do you have any suggestion for solving this problem (such as using special crystal or capacitor P/N).

    Any help and feedback is appreciated.

    Thanks, 

  • 0 in reply to amir mirbagheri
    TI__Guru**** 171519 points

    Hi,

    One additional idea that occurred to me is the load capacitance to the crystal itself. Your part number ECS-.327-12.5-13FLX-C seems to require a CL of 12.5pF. You are using a pair of 15pF capacitor which, in addition to the parasitic PCB tracks, might be either under or overloading the crystal.

    To calculate this, check section 6.3 of the application note SWRA640.

    Best regards,

    Rafael

  • 0 in reply to desouza
    Prodigy 120 points

    Hi,

    I used 15pF because I tried to follow TI design of CC2530EM. In designing EM , TI used 15pf capaciotr and I used the same P/N in my design.

    The only thing is TI uses another 32KHz crystal (P/N: MC-306 from Epson)  in CC2530EM. 

    Unfortunately, this part was out of stock at the time of design because of supply chain issue and I had to use another crystal with exactly same specifications 

     CL is12.5pF for both parts.The equvalent capacitance from crystal side is 7.5pF. I assume 5pF of parasitic capacitance that is added to this value that makes the whole capacitance to 12.5pF.

    Regards,

    Amir