Question about Crystal Oscillator Startup Speed in MFRC523 Chip

[Y1qdefrsgfsgsr]

I’ve been working with the MFRC523 contactless chip and noticed that its crystal oscillator startup speed is very fast. According to my tests, after pulling the reset pin high, the oscillator starts up in just about 3 to 4 microseconds. This speed is much faster compared to other contactless chips available on the market.

I would like to ask the engineers here how the MFRC523 achieves such a quick crystal oscillator startup time. Specifically, are there any special design techniques or optimizations used in the crystal oscillator circuitry?

Looking forward to your insights and answers. Thanks!

[Tomas_Parizek · Accepted solution]

Hello @Y1qdefrsgfsgsr , 

Let me use the "another" IC as an example.  Once the Reset signal is released, the IC starts with its boot which typically consists of  a two parts.

It is Analog and Digital boot where all power supplies and digital cores are initialized. The XTAL gets started after these two boots are done. The "boot" time depends on the architecture of the NFC IC (functions, ROM size etc...). 

About your second question. 

If the IC is in (soft) hard power-down mode, only a minimum peripheries of the IC are power-up and running. This ensures a very small current consumption. 

If the IC is in active mode (no RF but cliock is running), the current consumption might be a few mA depending on the used IC. 

Please also note that MFRC523 is very old product (around 20 years old). So it very depends on what IC from another company are you using for comparison. If you compare 20 old years product with some current IC, I can imagine such differece. 

BR

Tomas 

[Tomas_Parizek]

Hello @Y1qdefrsgfsgsr , 

The XTAL start-up time for our products is typically in the range of 0.3 - 1 ms. This also strongly depends on the used XTAL + XTAL oscillator PCB layout. 

Our products typically use a standard Pierce oscillator.

Newer products like PN5190, PN7642 and PN7220 contain an XTAL boost mechanism which increases the "gm" value during XTAL start. That helps to speed up the XTAL start. But still, the XTAL start is typically in the range of hundred microseconds. 

Can you share more details about your measurement? Do you have some waveforms (e.g.  XTAL2 signal)

Btw. we have a new app. note dealing with the XTAL oscillators -> https://www.nxp.com/docs/en/application-note/AN14518.pdf
You can have a look. 

BR

Tomas 

[Y1qdefrsgfsgsr]

@Tomas_Parizek 

Thank you for your response. I will carefully review the document you provided. Regarding the signal testing process, I have included the details in the attachment for your reference. I hope this information will help us make progress together.

Additionally, I tested the current of the RC523 on my custom EVB board. In one of the test items, there was an anomaly: in the soft power-down state, the circuit current was 2.19μA; while with the crystal oscillator on and no field switching action from the chip, the current was 7.07mA. In comparison, another company's NFC chip showed current values of 0.94μA and 952.87μA under the same conditions. When only the crystal oscillator is turned on, the current for the RC523 is noticeably higher. I am wondering if this could be an issue with my test method? Also, when you perform your tests, what is the current value when only the crystal oscillator is on? I couldn’t find the corresponding parameter in the datasheet.

Thanks!