nRF52823 HFXO DC specificaiton

[JGP_Kenji]

Hiya,

Regarding voltage amplitude peak to peak for external high-swing clock HFXO 32MHz, what's supply rails？I don't find out this specification defined in datasheet PS_V1.2.

Thanks Kenji

[Jørn]

Hello JGP_Kenji

Unfortunately the high frequency clock (HFCLK) of the nRF52 series does not support use of an external clock source. The only valid sources for HFCLK are the internal oscillator, or the 64MHz crystal oscillator. Do note that the crystal oscillator must be running for the RADIO and NFC modules to work.

EDIT:

The following comment was supplied by our designers

Based on simulations the peak-to-peak oscillation amplitude on XC1 and XC2 can range from appx. 0.3V to appx. 1.1V, depending on crystal selection, load capacitors, process variation, operating temperature and supply voltage. The amplitude is usually slightly bigger on XC2 than on XC1. The DC offset is typically around 0.5V. When doing voltage measurements on XC1 and/or XC2 it's important to use a low-capacitance active probe. A regular passive probe will add too much load capacitance. The probe should also have an input resistance of at least 10Mohm.

In order to verify that the load capacitors are optimal, it's best to measure TX carrier frequency.

Best regards

Jørn Frøysa

[Jørn]

I may have worded my previous message a bit clumsily, I apologize for that. The HFCLK receives its clock signal from 1 of 2 sources. The internal RC oscillator (HFINT), or the internal crystal oscillator (HFXO). Both are located on-chip. An external crystal is necessary for the internal crystal oscillator to run. The crystal oscillator's power supply is located on-chip and it is not necessary to supply it with voltage. All that is needed is a quartz crystal within the specifications stated in the product specification, along with appropriate tuning capacitors.

What I meant by external sources is you cannot supply a 32MHz signal from an external, off-chip, oscillator.

I struggle with understanding what the supply voltage you mention is. You do not need to supply any voltage other than VDD, as stated in the reference schematics.