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TBCLK specifications & requirements

Gerardo Vanoni
Prodigy 240 points

Hello,
what are the specs of the TBCLK-input and what are it's requirements?

My application has 12x LDC1000, therefore it would be easier & cheaper to use only one external oscillator, instead of 12x crystal.

But to dimension / choose the proper external oscillator, Cin or load data from TBCLK-input should be known (data is missing in datasheet). Can you please give me that figures, both for 3.3V and 5V?
Is it admissible to form a "daisy chain", connecting XOUT from one LDC1000 to the TBCLK-input of the next one?

How important is the symmetry (duty cycle) of the external clock? Depending on type (and price) duty cycle specs varie i.e. between 40%/60% to 45%/55% or 50%/50%.

Thanks & regards,
Gerardo

  • 0
    TI__Genius 9300 points

    Hello Gerardo,

    I forwarded your question to the design team, and will update you once I got the answer.

    Regarding the duty cycle, 40%-60% spec is fine.

  • 0 in reply to Evgeny Fomin
    Prodigy 240 points

    Hello Evgeny,

    heard anything...?

    Best regards,

    Gerardo

  • 0 in reply to Gerardo Vanoni
    TI__Intellectual 2790 points

    Hi Gerardo,

    The Cin is very small, worse case is ~5pF.  So O(1000) pins can be driven with just a MSP430 pin alone in the ideal case. 

    Since you indicate that you would like to drive multiple LDCs with a single crystal, that is not recommended.  The reason for this is oscillation is not guaranteed due to varying Cins across various devices.  You can try buffering the output of the crystal to drive the TBCLKs of the other 11, but again, this particular method is not supported.

    XOUT is disabled when TBCLK is input and should be left floating.  Therefore, you cannot daisy chain TBCLK; you can, however, drive multiple TBCLKs from a single star point.

    The way it is done on the EVM is to divide a MCU crystal clock out to a MCU pin that drives TBCLK.

    Thanks,