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MSP430F5418A: Resonator issue

Fjs
Intellectual 360 points
Part Number: MSP430F5418A

Hello,

i have an issue with a resonator and the MSP430F5418A. I use a Murata resonator (CSTCR-Type with a 1M feedback resistor) on XT2 for baud rate generation (19200 Baud). XT1 is connected with a 32kHz crystal. Round about 60% of the boards are running without problem. On the other boards the resonator on XT2 do not start.

My C code for switching on the resonator is basically the same as the example in http://dev.ti.com/tirex/explore/node?node=ACoy4yJShU2Q1xsx2hWfFw__IOGqZri__LATEST

Best regards

Frank

  • 0
    TI__Mastermind 38615 points

    Hi 

    The XT2 is used to input clock for high speed rang in 4M~32M. You should set correct Vcore and matching capacitor. For more information about the parameters you can refer to the datasheet page49 http://www.ti.com/lit/ds/symlink/msp430f5438a-ep.pdf

    Best regards

    Gary

  • 0
    TI__Intellectual 2100 points

    Hi Frank,

    I looked into the datasheet of the CSTCR type of resonators. It is a high cap type, meant to be even running and low noise...  even on a high speed silicon components with harsh transients. 

    ...and here is the catch: To stat an oscillation you need a loop amplification that is bigger than one, a loop phase of 360 deg.  and a frequency determining element. Our Oscillator circuit is meant for lowest power and it is gentle to XTALS to avoid any frequency errors. Combining those two components might cause a very long startup time. Since the '430 does not generate enough eigen-noise , and the CSTCR would attenuate the existing noise away....

    But there is help... you can use a jumpstart element that generate enough initial energy to start the oscillator. Below are two approaches.

    Analog: you use a regular diode and connect it between VCC and XT2IN in reverse direction (cathode towards VCC). This gives an initial pulse during power up to start the resonator. Here the nonlinear parasitic varicap/varactor property of the diode is used to start things.

    Digital: you use the XT2OUT as output port and toggle a couple of times. This causes the XTAL to get moving; then configure back to oscillator mode => Done.

    have a nice day

               Johann

     

     

  • 0 in reply to Johann Zipperer
    Intellectual 360 points

    Hello Johann,

    i tried out both of your solutions. My first try was the digital solution. Some of the boards worked now and some not. So i think you have right idea.

    Additional i tried the analog solution on one board, but it didn't work there.

    I think the best way ist to exchange the resonator to another resonator which fits better. Do you know a resonator which is ideal for the MSP430 oscillator unit? My requirements is small-size and and frequency lower or equal than 8MHz.

    Best regards

    Frank

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