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TL16C554A: crystal oscillator network

Jason Shen
Intellectual 1945 points
Part Number: TL16C554A

Dears

I have a customer plan to use the TL16C554A for the uart application, but there have a help need for the crystal  oscillator network  which mentioned in the datasheet.

1. customer will use 14.7456Mhz crystal  oscillator , how to design the RX2, C1, C2 mentioned in the datasheet Page36.

2. the Gain of the oscillator amplifier or Gm.

3. there have a parameter in datasheet Page8, Clock input capacitance/ Clock output capacitance, what does this means? it will apply to the crystal  oscillator conditional? with 14.7456Mhz crystal  oscillator.

Thanks

Jun Shen

  • 0
    TI__Guru 60422 points

    Jun,

    Our UART expert has been notified of this thread and will respond accordingly.

    Regards,

    Eric Hackett 

  • 0
    TI__Mastermind 49410 points

    Hi Jason,

    Jason Shen said:
    1. customer will use 14.7456Mhz crystal  oscillator , how to design the RX2, C1, C2 mentioned in the datasheet Page36.

    The crystal datasheet should provide you with those values. You basically just look to see what the manufacturer spec's for the load capacitance. If they spec a typical of 18pF for example then you would choose 2 caps that are about 2x that value like 36pF. So C1 and C2 would be 36pF. 

    Jason Shen said:
    2. the Gain of the oscillator amplifier or Gm.

    You don't have control on this. 

    Jason Shen said:
    3. there have a parameter in datasheet Page8, Clock input capacitance/ Clock output capacitance, what does this means? it will apply to the crystal  oscillator conditional? with 14.7456Mhz crystal  oscillator.

    You're technically correct. The input capacitance will added in parallel with the loading capacitance. From my experience, this hasn't caused any issue to my oscillator circuits before, I usually pick slightly lower values for the loading caps. In my above example, I said 36pF but you could probably use something like 20pF and assume the input capacitance will add up to close to 36pF. 

    -Bobby

  • 0 in reply to BOBBY
    TI__Intellectual 1945 points

    Bobby

    Thanks for the help.