S2-LP Custom Board - Need help

Silas Valera · ‎2018-01-06

Posted on January 07, 2018 at 03:35

Hi

I have my custom RF board using S2-LP and balunBALF-SPI2-01D3 (

/external-link.jspa?url=http%3A%2F%2Fwww.st.com%2Fcontent%2Fccc%2Fresource%2Ftechnical%2Fdocument%2Fdatasheet%2Fgroup3%2Fe9%2Fff%2Fcd%2F1e%2F4f%2Fdd%2F49%2Fb4%2FDM00417488%2Ffiles%2FDM004174pdf%2Fjcr%3Acontent%2Ftranslations%2Fen.DM004174pdf

) and my custom board follows the evaluation design given in the balun data sheet. I am having problem with it:

The host controller communicates fine with S2-LP over SPI (I can see the expected signals on oscilloscope for SCL, SDI, SDI and CS). Also SMPS 1 and 2 (pins 2 and 3 of S2-LP) show expected waveforms. But there is not signal on TX pin. Can anyone help me please?

Thanks

Silas Valera

#868-mhz #custom-board #s2-lp #balf-spi2-01d3

Note: this post was migrated and contained many threaded conversations, some content may be missing.

Winfred LU · ‎2018-03-22

Posted on March 23, 2018 at 05:19

Hi Silas,

Agree that 0x1F and 0x2F in SYNT0 do not make much difference. I was just trying to make sure the tests were apple to apple comparison.

Could you please also doubly check if the crystal works correctly?

About S2LP evaluation boards, currently none of the EVBs (STEVAL-FKI868V1 and

STEVAL-FKI868V2

) come with BALF-SPI2-01D3.

About the circuit, i will leave for some RF export to comment further.

Thank you.

Best Regards,

Winfred

Silas Valera · ‎2018-03-27

Posted on March 28, 2018 at 04:08

Hi Winfred,

I checked the crystal and it works perfectly fine.

I will soon receive the next versions of PCBs for S2LP with discrete balun (caps+inductors) and S2LP with chip balun and will soon test those versions.

Yes, the purpose for using the chip balun is reduce component counts and better reliability. So I look forward to testing the new version.

I did not get one thing though! The S2LP is a chip with better specs than SPIRIT, then why does it need so many external components than SPIRIT? The SPIRIT with BALF needs just 11 components (i.e. crystal, load caps, and other SMPS inductors and capactors) which would make it so easy and simple (

http://www.st.com/content/ccc/resource/technical/document/datasheet/f2/4f/6c/86/c0/b6/4a/f8/DM00091076.pdf/files/DM00091076.pdf/jcr:content/translations/en.DM00091076.pdf

), whereas S2LP with BALF would need way more components. The only advantage which I am considering S2LP over SPIRIT is the Rx/Tx currents (7mA and 10mA for S2LP over 9mA and 21mA for SPIRIT) and of course the Rx sensitivity. Hope I can get these rated currents for S2LP as stated in data sheets.

Thanks!

Silas

Winfred LU · ‎2018-03-28

Posted on March 28, 2018 at 07:15

Hi Silas,

Again, need to state that I am not an export for RF circuits.

But it seems to me that

components forBALF-SPI2-01D3 would be simpler.

BALF-SPI-01D3 has 2* L and 3* C connecting to SMPS Ext1 while

BALF-SPI2-01D3has 1* L and 1* C connecting to SMPS.

This is schematic for BALF-SPI-01D3:

And this is the schematic for BALF-SPI2-01D3:

Best Regards,

Winfred

Anton Olofsson · ‎2018-04-12

Posted on April 12, 2018 at 13:55

Hi Silas,

Hope you are making progress!

Have you double checked that TX-line between S2 and BALUN is connected to SMPS2 as seen on p.5 here (VSMPS2):

http://www.st.com/content/ccc/resource/technical/document/datasheet/group3/e9/ff/cd/1e/4f/dd/49/b4/DM00417488/files/DM00417488.pdf/jcr:content/translations/en.DM00417488.pdf

Did using discrete components instead of balun help?

Silas Valera · ‎2018-04-12

Posted on April 13, 2018 at 04:04

Hi Anton,

Thanks for your thoughts and suggestion! Yes I am following exactly the same schematic - the one in the updated version of balun reference manual. I have actually compared the voltages between the S2LP Eval board and my board and they are similar. The one with discrete components also behaves similarly, get a very flat output and not a nice spike @868Mhz on spectrum analyzer. Both the versions are two layer pcbs and also I did not follow exactly the transmission tracks length guidelines, I was following the older version. But after that test, I have designed 4 layer pcb and have taken all possible care to follow the guidelines. My samples boards should arrive in couple of days. I am very much hiopeful this time Will soon post the results!

Best regards

Silas

Silas Valera · ‎2018-04-14

Posted on April 15, 2018 at 01:11

Hi All

I received my sample boards, this time with 4 layers and guidelines followed exactly, assembled one and tested!! Works perfectly fine!! I compared with the S2LP EVAL board for the performance, and seems to give me almost comparable results! Both modes TX and RX work good.

Thank you all!!

Silas

Anton Olofsson · ‎2018-04-16

Posted on April 16, 2018 at 08:33

Very nice to hear Silas!

To be honest i did not think it would be that sensitive to the layout.

Thank you for sharing and best of luck going forward!

Best,

Anton

Silas Valera · ‎2018-04-18

Posted on April 19, 2018 at 04:14

Hi Anton,

Thank you so much for your best wishes!

Yes, the RF PCB design is very much sensitive to many factors like component layout, components case/size, interconnecting traces, ground planes, ground vias, dielectric propperties of substrate, pcb thickness, Cu layer thickness etc.. There are many resources on the web for startup design and then fine tuning for best impedence matching for best sensitivity in Rx mode and max power tansfer in Tx mode. Generally transceiver IC manufacturer provides good guide lines and would give best results. Thanks to ST for the updated version for balun datasheet whichprovidesreference layout which makes the layout design very easy! Most important I think, is the microstrip width, there are online calculators available for this. Of course this

(

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)

guide is generally helpful too.

Best

Silas

BMoha.19 · ‎2019-05-19

Hi @Silas Valera

I can't display S2-LP register in my board (i can display them in ST eval board STEVAL-FKI868V2).

is there a specific configuration to dispaly S2-LP register soldered in my board?

Thanks in advance.

Silas Valera · ‎2019-05-27

Hi @BMoha.19

I understand that yours is a custom S2-LP board. Please make sure the pcb design follows the guidelines. Do you use the balun or discrete components? In either case, make sure the S2-LP chip and components are soldered right and there is no bridge. With all the precautions/guidelines followed, your board should work as expected.

With you all the best!