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TIDA-00721: TIDA-00721

Binh Nguyen Thanh94
Prodigy 230 points
Part Number: TIDA-00721
Other Parts Discussed in Thread: TIDA-00271, RF430CL330H, TIDA-00217

Hello everyone,

I've read the document of TIDA-00721 Passive NFC Temperature Patch Reference Design. As I know, the voltage harvested from NFC is different across the smartphones and depends on the distance. If the voltages vary significantly or they are too high, the embedded system may be damaged, but I didn't see any component in the schematic that plays a role as a voltage regulator to stabilize and limit the harvested voltage, I don't know what the reason is, anyone please help me, thank you so much.

Binh 

  • 0
    TI__Genius 12780 points

    Hi Binh Nguyen Thanh94,

    The description given in TIDA-00271 ( ) gives a good description of what is happening with the voltage harvested from the antenna. Please note both the TIDA-00721 and TIDA-00271 use an almost identical antenna front end.

    The datasheet for the RF430CL330H  gives some information, and it looks like there is a voltage clamper that keeps the voltage below 3.6V (< 70 mA).

    You may want to ask a question on the RF430CL330H if you would like additional information in regard to the voltage regulation.

    Best Regards,

    Dan

  • 0 in reply to dBrock
    Prodigy 230 points

    Hi Dan,

    Thanks for your help. One more thing I want to know is that what is the maximum voltage can be applied for the internal voltage clamber of the RF430CL330H, I usually get a very high voltage from the NFC of a smartphone so I afraid the MCU and sensors might be broken. Additionally, I see in TIDA-00217 and TIDA-00721 that the antennas are both small and they seem the minimum dimension you can draw, but I am wondering how did you ensure that those antennas will harvest enough energy for the embedded system.

    Best Regards,

    Binh

  • 0 in reply to Binh Nguyen Thanh94
    TI__Genius 12780 points

    Hi Binh,

    Please post your question about the voltage clamper of the RF430CL330H in the NFC/RFID Forum here on E2E  Also, if my answer below is not what you are looking for, I would follow up in the above mentioned forum since their expertise is in NFC/RFID applications.

    As for the antenna design, the antenna length was determined by the NFC operating frequency (13.82 MHz), and the shape of the antenna was determined in order to minimize the amount of PCB board space used. The antennas must be tuned in order to ensure maximum power transfer at 13.82 MHz. Things like making sure the reflection coefficient (S11) is below -20 dB at 13.82 MHz (including the bandwidth you care about). This snip from TIDA-00217 talks a little about it.

    Once the antenna is tuned to deliver max power at your operating frequencies, the power "harvested" from the receiving antenna is mainly a function of distance and how much power is being radiated by the transmitting antenna. Both TIDAs show that the receiving node doesn't "respond" until the transmitting NFC device is a couple of centimeters away, meaning that the 3V rail is "energized" at this distance. Unfortunately, I don't have any other information on the matter.

    Best Regards,

    Dan

  • 0 in reply to dBrock
    Prodigy 230 points

    Hi Dan,

    I would like to know what did you mean by the sentence "the antenna length was determined by the NFC operating frequency (13.82 MHz)". Are there any relationship between the total length of the antenna coil and the wavelength?thank you.

    Best Regards,

    Binh

  • 0 in reply to Binh Nguyen Thanh94
    TI__Genius 12780 points

    Hi Binh,

    Yes, antenna length is directly connected to frequency. Please take a look at this link 

    There are a lot of resources available on the internet in regard to antenna sizing and theory.

    Best Regards,

    Dan