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TMS320F28035: TMS320F28PLC84PNTR / Crystal accuracy

Caglar Cihan
Expert 6235 points
Part Number: TMS320F28035
Other Parts Discussed in Thread: TMS320F28PLC84

Dear Team,

Our customer previously designed a PLC project with TMS320F28PLC84. They are now in production phase and they had some supply issues with the parts on the design. One of these parts is the crystal. It is recommended to use 20ppm max device on the design, but the one they were able to find has 30ppm max specification.

Do you think it is OK to use this device?

Best Regards,

Caglar

  • 0
    TI__Guru* 80220 points

    Caglar,

    I think this will be fine, I believe that the 20ppm is more or less industry standard, which is why it is suggested.  Comparing 30ppm vs 20ppm we really care about the max error, since it will result in the device running faster. 

    The difference here is minimal, assuming they are using 10MHz X-tal, and multiplying by 9(90MHz max frequency) we get 90.0027MHz @30ppm vs 90.0018MHz @20ppm.

    If customer were using our internal 10MHz oscillator that spec is ~+/-3% variance, and we can support this fully, which would give 92.7MHz.  Above is well below that.

    So, from a chip operation standpoint I see no issue.  It would be up to the customer, especially for a communications based application to determine that deviation won't cause any issues downstream.  But I would assume that has already been done.

    Best,

    Matthew