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

[JGP_Kenji]

Hello Jorn,

Sorry for I didn't clear up my requirement in detail, it causes misunderstanding.

In terms of external clock source to nRF52832, I designed in Xtal 32.768kHz on LFXO and Xtal 32MHz on HFXO,right now I'd like to know the DC specification what min.and max. input voltage level of HFXO are.

Thanks Kenji

[Jørn]

Unfortunately we do not have any numbers on what the voltage swing will be at the HFCLK crystal pins during HFCLK operation. My apologies, I'm still not sure what you mean by min and max values input voltage level, there should not be any power supply, external clock source or signal generator connected to the XC1 and XC2 pins (pin 34 & 35). To ensure proper operation only a crystal with two capacitors should be connected to the pins, as shown in reference circuits section 53 of the product specification.

[JGP_Kenji]

Hi Jorn,

I'd like to know the specification for HFXO 32MHz likes Vamp_in_xo_low defined in datasheet for LFXO 32.768KHz

Thanks Kenji

[Jørn]

Unfortunately we do not have any numbers for that, as the HFCLK is not designed to receive a clock signal from an external source. The LFCLK is specifically designed to be able to receive a clock signal from an external oscillator, which is why those numbers are included in the specification.

[JGP_Kenji]

More confusion for me.

The section of Nordic nRF52832 datasheet, Clock - clock control, there are two signal sources to HFLCK in the block diagram, HFINT internal oscillator and HFXO Crystal oscillator.

However, I saw "The HFXO is started by triggering the HFCLKSTART task and stopped using the HFCLKSTOP task. A HFCLKSTARTED event will be generated when the HFXO has started and its frequency is stable"

All in all, my understanding is HFXO must be running to use RADIO and NFC module, I have designed those wireless functions in product and just would like to know the input voltage level of HFXO Crystal oscillator, not HFCLK.

But you mentioned HFCLK isn't designed to receive a clock signal from an external source,which mean HFXO crystal oscillator in chip isn't working in fact？The only clock signal to HFCLK, is HFINT？

Pls. clarify if any.

Thanks Kenji