HXFO pin capacitance (Cpin)

[MURAKAMI KAZUHIRO]

nRF54LM20A: 

C_pin is the pin input capacitance on pins XC1 and XC2.

Could you provide the typical, maximum, and minimum values of Cpin?

This information is needed as a reference for external 32 MHz crystal tuning.

[Simonr]

Hi

The Cpin_HFXO input capacitance capacitance typical value is listed in page 1261 of the nRF54LM20A datasheet: https://docs-be.nordicsemi.com/bundle/ps_nrf54LM20A/page/pdf/nRF54LM20A_nRF54LM20B_Datasheet_v1.0.pdf 

We don't have maximum or minimum values specified I'm afraid, is there a reason you specifically need that?

Best regards,

Simon

[MURAKAMI KAZUHIRO]

Thank you for reply.

When determining the value of the external capacitance, I would like to take the tolerance of Cpin.
Although ±40 ppm is recommended for BLE operation,is it acceptable not to take the tolerance of Cpin ?

best regards,

[Simonr]

Can you explain what you mean by "take the tolerance of Cpin"? Is this a value you want from us?

Best regards,

Simon

[MURAKAMI KAZUHIRO]

The HFXO load capacitance specification of the nRF54LM20A is 6–9 pF.

When designing the external capacitors, we would like to confirm whether the resulting CL stays within this range when considering the tolerance/variation of Cpin.

[Simonr]

Hi

Please see the OSCILLATORS chapter for how to calculate the load capacitance when using external capacitors:

When using external capacitors, the load capacitance (CL) is the total capacitance seen by the crystal across its terminals and is calculated by the equation above. C1 and C2 are the external capacitors. Cpcb1 and Cpcb2 are stray capacitance on the PCB. Cpin is the pin input capacitance on XC1 and XC2. When you use the external capacitors you should disable the internal capacitor by setting OSCILLATORS.XOSC32M.CONFIG.INTCAP to 0.

Best regards,

Simon