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RFID Design with TMS3705

Vincent Lin
Prodigy 70 points
Other Parts Discussed in Thread: TMS3705, RI-STU-MRD2, UCC27424

Does any body knows whether I can hook an 27UH antenna to RFID system using TMS3705?

From this document:

 http://www.ti.com/lit/an/scba031/scba031.pdf

It is recommended to use antenna inductance between 100uH to 400uH. 

In my design, I would like to use 27uH antenna instead. Not sure whether I can do so?

Regards,

Vincent

  • 0
    TI__Guru* 91186 points
    this is not recommended directly - you can either implement circuit i posted in the first response to this post e2e.ti.com/.../1747616 or move to RI-STU-MRD2 (which needs 47uH antenna, which is something you can implement on PCB, if that is the motivation)
  • 0 in reply to Josh Wyatt
    Prodigy 70 points

    Thanks Josh. 

    I have looked at previous posts you had replied. I wanna confirm with you whether I can do as below for a new RFID design.

    For example like the file attached:

  • 0 in reply to Vincent Lin
    TI__Guru* 91186 points

    yes, I agree that the combination of 27uH and 52nF make resonance @ 134.4kHz, so this should work. if you added another 145pF you would be mathematically perfect at 134.2kHz

     

  • 0 in reply to Josh Wyatt
    Prodigy 70 points

    Hi Josh,

    I consider to use 27uH rectangular antenna which has length of 1 meter and width of half a meter. I expect to use it for 1 meter read range. This will require current driver provides with higher current. (I design for +12V or +24V supply)

    1. Would Si4532ADY sufficient for my design? 

    2. How about using UCC27424:

    http://www.ti.com/lit/an/scba031/scba031.pdf

    Which is better? If i use option 2, I may not need to buy other ICs such as NAND Gates, NOT Gates, current driver etc.

    Regards,

    Vincent

  • 0 in reply to Vincent Lin
    TI__Guru* 91186 points

    how big is the tag you are using? for this range you want its needing to be greater than 30mm in diameter (i.e. our disk or larger, made from our HDX silicon)

    to get 1m read range with LF, and with an antenna that large you need an amplifier that is putting out 10 to 20 Watts, not 100 -200mW.

    please see ==> RI-RFM-007B, plus the RI-CTL-MB2B or RI-STU-251B, either with RI-ANT-G01E, will produce this sort of max read range chart you see below

  • 0 in reply to Josh Wyatt
    Prodigy 70 points
    Hi Josh,

    I am looking at 32mm disk tag.

    If I replace Si4532ADY to IRF540 or IRF5210 in the reference design given by you, would it work? Do I need to consider to put any other protection circuit or components?

    Regards,
    Vincent
  • 0 in reply to Vincent Lin
    TI__Guru* 91186 points
    Vincent -
    You will not get the range unless you basically recreate what is on the RFM-007B...the circuit on there is a push pull, being driven by an older ASIC which is similar to the TMS3705, which is the heart of the LF reader, but then it employs a custom step up transformer and onboard high voltage binary tuning capacitor array. the levels seen here on the antenna will be hundreds of volts, which is what you need to have for this kind of system.

    so, i hope its clear that just an ASIC doesn't have all what is needed to get the range - you need an RF amplifier circuit which is suitable in both power and power rating, along with a high Q antenna to get the range like this.

    you might be tempted to connect a high Q antenna to the TMS3705 to get the range. Seems like it would, but one of my colleagues who was following this post reminded me that the low end where the IC could shut off the TX is around 220mA. the range of this possible and expected shutdown area is from 220mA up to a bit above 1A. it does this to protect itself when a level is crossed it knows is head towards an over-current situation, so please always use a low Q antenna (around 10 or so is OK) with the TMS3705.

    thanks!