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AM67: AM67 Load Capacitor Calculation Discrepancy

Nicolas Rancher
Prodigy 85 points

Part Number: AM67

Hi TI team,

Seems there is a discrepancy with the load calculation for the AM67.
The equation your AM67 datasheet is displaying right below figure 6-18 seems to not
follow the standard equation C_L = ((C_L1 * CL*2)/(C_L1 + C_L2)) + C_stray + C_pin...
Could you please clarify the calculation provided in 6.11.4.1.1.1 of the AM67 Datasheet?

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  • 0
    TI__Intellectual 1380 points

    Hello Nicolas,

    The equation in the AM67x Datasheet in section 6 Specifications, point 6.11.4.1.1.1 Load Capacitance is correct and consistent with the standard crystal load capacitance formula. Rather than lumping parasitics into a single C_stray + C_pin term, TI's equation explicitly accounts for the PCB trace parasitics (C_PCBXI and C_PCBXO) and device pin capacitances (C_XI and C_XO) separately for each signal node. This is actually more accurate, as it gives the designer full visibility into each parasitic contribution. There is no discrepancy- the formulas are mathematically equivalent.

    Best Regards,

    Borislav Lazarkov

  • 0 in reply to Borislav Lazarkov
    Prodigy 85 points

    Okay, thank you for the clarification. As for WKUP_LFOSC, are there known pin capacitance values similar to MCU_OSC?