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LP-MSPM0L1306: What applications that require +/- 1% accuracy across temps?

Part Number: LP-MSPM0L1306
Other Parts Discussed in Thread: MSPM0L1306

Hi, 

May I know in what applications that require +/- 1% accuracy across temps? (e.g. connecting ROSC pin with 0.1%, 25ppm resistor)

If I2C 400KHz is the highest interface speed in our application, should we need "connecting ROSC pin with 0.1%, 25ppm resistor" ?

Thanks

  • Hi Alex,

    Welcome to the E2E forums. 

    Typically oscillator accuracy requirements are more of an end-application consideration, but I can try to provide some guidance. It necessarily won't be determined by the highest speed peripheral in your system, but usually by the allowed mismatch between either two devices, or between your device and some interface with the real world. 

    For I2C you typically don't have to worry at all about clock mismatch, because there is a dedicated clock line between controller and target. If however you are using UART across temperature, we typically budget +/-3-5% baud rate mismatch between the two devices communicating, and the error from both sender and receiver needs to be considered here. So your clock at any one end really needs to be between 1.5% - 2.5% accurate, or you risk communication error. CAN Bus (not supported on MSPM0L1306, but is available on MSPM0G3x devices), is another asynchronous interface that you would want this resistor, or an external clock source for. 

    This is true for both of these communication protocols, regardless of frequency, because there are matching requirements for the transmissions to be performed correctly. 

    Beyond asynchronous communications, you would need to determine if your system can tolerate, or would even notice, if something like your internal timers were 1% off instead of 2.5% off. Is it okay in your application if you are now checking a sensor value every 0.975s - 1.025s? Or does it need to be every 0.99 - 1.01s? 

    Best Regards,
    Brandon Fisher

  • Thanks Brandon

    If I understand correctly- Besides the timer reading, the 1% clock tolerance is mainly for asynchronous communications accuracy (CAN bus).

    And no worries for synchronous interface like I2C, since there’s a clock between controller and target.

     

    While thinking of the timing parameters like I2C operates in either master or slave mode-

    Will the higher clock tolerance (+/- 3.3% when SETUSEFCL=0, -40 ℃ ≤ Ta ≤ 125 ℃, as picture below) affect the timing parameters like setup time, hold time…etc?

     Does MSPM0L1306 use internal timer to work on I2C timing parameters like setup time, hold time…etc?

    //Table below- I2C timing parameters of MSPM0L1306

    Best Regards

    Alex

  • Hi Alex,

    The I2C timing specifications from the datasheet will hold regardless of the presence or absence of that ROSC resistor. All that might shift is the actual SCL clock frequency when you are in controller mode. 

    Best Regards,
    Brandon Fisher