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PC16552D: Could you please tell me how to choose the crystal can be used for PC16652D?

Kazuya Nakai59
Guru 21515 points

Part Number: PC16552D

 Hello guys,

 One of our customers is using PC16552D for their current products. But recently they knew the crystal could no longer be ordered because the crystal was discontinued. The crystal part number is AT51CD2 18.432MHz. The spec is in the following URL.

http://www.ndk.com/en/products/discon/pdf/c_AT-51-STD-PFE-2_e.pdf

 So they want to know how to choose new crystal can be used for the device instead of AT51CD2.

Could you please tell me how to choose a crystal can be used for PC16652D for them?

Also we think the following crystal may be used for the device.

HCM4918432000ABJT    (18.432 MHz)
http://cfd.citizen.co.jp/english/prod-tech/product/pdf/datasheet_AT/HCM49_E.pdf

  Is our thinking correct?

 Your reply would be much appreciated.

 Best regards,

 Kazuya Nakai.

  • 0
    TI__Guru 62920 points
    Nakai-san,

    Yes, this replacement device looks like it should work. You may need to adjust some of the R/C components in the oscillator circuit based on recommendations in the crystal datasheet, but otherwise it looks like this would serve as a drop-in replacement.

    Max
  • 0 in reply to Miguel Robertson
    Guru 21515 points
    Hello Max,

    Thank you very much for the prompt reply.

    Could I ask you a few additional questions?

    1.Do you have any recommendation value for the following parameters of crystal for PC16652D?
    (1) R1：Series Resistance (Motional Resistance)
    (2) L1；Motional Inductance
    (3) C1：Motional Capacitance
    (4) Co：Shunt Capacitance

    2. Your said the R/C components in the oscillator circuit should be adjusted based on recommendations in the crystal datasheet. If crystal datasheet doesn't have any recommendation value, how we adjust the R/C components (RP, RX2, C1, C2 on page 15 on PC16652D datasheet (SNLS387B).

    Could you please give me your advice?

    Thank you very much again and best regards,
    Kazuya Nakai.
  • 0 in reply to Kazuya Nakai59
    TI__Guru 62920 points
    Nakai-san,

    I just mentioned that because I noticed that the HCM49 crystal specifies a load capacitance of 10 pF while AT-51CD specifies 16 pF. So, you may want to adjust the external capacitance values accordingly so that they are optimal for the crystal. This would affect C1 and C2. RP and RX2 could remain the same values.

    Max
  • 0 in reply to Miguel Robertson
    Guru 21515 points
    Hello Max,

    Thank you for your reply. The customer wants to know whether TI has the recommend X'tal parameters (R1, L1, C1, Co ) value or not. Is the answer no?
    Also they want to know which higher priority parameter is in R1, L1, C1, Co. Is it R1?
    And they want to know whether TI has any formula to calculate R/C components (RP, RX2, C1, C2). Is the answer no?

    Could you please give me your reply?

    Thank you and best regards,
    Kazuya Nakai.
  • 0 in reply to Kazuya Nakai59
    TI__Guru 62920 points
    Nakai-san,

    We don't have recommended values for these parameters or formulas to calculate the optimal parameters. In general, though, I would suggest choosing a crystal with the appropriate frequency and then tuning C1 and C2 to match the load capacitance required by the crystal (also accounting for PCB parasitic capacitances and pin capacitances). The resistance values can remain the same in most cases, although some adjustments may be needed if using a crystal with significantly higher series/motional resistance (>100 Ohms).

    You may want to refer to this application note on crystal selection, although it was written with RF systems in mind which will generally have stricter requirements on clock accuracy than a serial UART:

    www.ti.com/.../swra372c.pdf

    Also, note that NDK's discontinued product index (www.ndk.com/.../index.html) lists the AT-41CD2 as a recommended replacement device. It looks like the specifications of this crystal are similar enough to the current crystal for circuit adjustments to not be required. You may want to consider this device as well.

    Regards,
    Max Robertson
  • 0 in reply to Miguel Robertson
    Guru 21515 points
    Hello Max,

    Thank you very much for your reply. I informed the customer your comment and advice.

    Thank you again and best regards,
    Kazuya Nakai.