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ADS1293: lead off clock

John Shambrom
Prodigy 85 points
Part Number: ADS1293

This part has an AC detection feature for determining lead impedance.  It is derived from a 50KHz clock.  I have found the clock frequency to be off by more than 2% on the particular board I am working with.  What is the tolerance of this on board oscillator?

John

  • 0
    TI__Genius 11550 points

    Hi John,

    Thank you for your patience. 

    Unfortunately, I checked with the team and didn't have any additional data to share for the internal oscillator tolerance. The accuracy of the internal oscillator depends on the external crystal and the external load capacitors. For better accuracy, you can provide an higher accuracy external CLK to the device through the CLK pin. 

    Thanks.

    -TC

  • 0 in reply to TCT
    Prodigy 85 points

    It doesn't seem possible that the 50.0KHz LOD oscillator is derived from the 4.096MHz crystal oscillator.  The ratio of the 2 is 81.92, how would you do that?.  Also, I confirmed that the crystal oscillator is very accurate, within 0.015%, and that the LOD clock is not accurate, high by 2.5%.  So it must be an internal free running oscillator.  Please look deeper.

    John

  • 0 in reply to John Shambrom
    TI__Genius 11550 points

    Hi John,

    I don't have access to the detail design implementation of clock distribution network on the device so I cannot comment on how the design is done in this case.  Since the device has been released a while back and getting such information is a little challenging. I have dig through all the information that I can get a hold off and as I said unfortunately I don't have the exact information that you are looking for. I will ask around to see how much more I can get. 

    Thanks.

    -TC

  • 0 in reply to TCT
    Prodigy 85 points

    I finally found out what's wrong with the design of this part - nothing.  The data sheet is wrong, the lead off clock is 4.096MHz / 80 = 51,200Hz, not 50,000.