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TRF7960 used only for power transmission?

dayberry
Prodigy 250 points
Other Parts Discussed in Thread: TRF7960, MSP430F2370, TRF7961

I have the TRF7960EVM and have been using it and its integrated coil antenna to transfer power to a parallel resonant circuit, which is just an unshielded inductor and tuning cap with Schottky diode. With the EVM I just plug it into USB and I can see it immediately at 13.56 MHz on the spectrum analyzer. For my application I am just putting the EVM in proximity to the receive circuit to charge a large electrolytic capacitor (2mF) which will power a very low power MSP430 for a few seconds. My question is how I might go about using the TRF7960 for this application. I will be doing no actual RFID data transmission I just want the TRF7960 to output power to the resonant circuit. What does the TRF7960 do upon startup if no microcontroller communicates with it?

  • 0
    TI__Mastermind 44220 points


    We have done some similar testing here powering MSP430 through inductive coupling at 13.56MHz with positive results.

    Unfortunately, I cannot see any way to turn on the RF output without having a microcontroller.  This is accomplished by writing to the Chip Status Control register (0x00).  For example, the TRF7960EVM will write a 0x21 to this register to indicate 5V supply and activate the RF field.  If this is the only function of the microcontroller, you could probably get by using a much lower cost MSP430 than the MSP430F2370 as used on the TRF7960EVM. 

    Let me know if you have questions.

    Best Regards,

    Eddie LaCost

  • 0 in reply to Eddie LaCost
    Prodigy 250 points

    I apologize if I was ambiguous in my  initial post; I am OK with needing to use a microcontroller in a limited capacity to communicate with the TRF7690, I just want to avoid complicated firmware on the MCU if I can help it. Do I just need to write a few registers to get the field activated? If so then that works great.  Out of curiosity in your similar testing did you use an antenna similar to the coil on the EVM or did you get better results with an external antenna?

     

    Brennan

  • 0 in reply to dayberry
    TI__Mastermind 44220 points

    Brennan,

    Yes, the code should be very simple.  You would only have to write one register to activate the field.  Please see table 5-9 of the datasheet for a description of the chip status control register.  B5 controls the RF field.

    http://focus.ti.com/lit/ds/symlink/trf7960.pdf 

    We have used the antenna on the EVM as well as other antenna types.  There are several factors that will affect the coupling.  Very good coupling is generally acheived when the coil on the TX and RX side is about the same dimensions.  If your TX coil is larger, you may acheive greater range, but current available on the RX end is not as great.  Orientation of the coils is very important for good coupling and ferrites can be also be used to help attract more magnetic field.  We used a credit card sized PCB coil attached to an eZ430-F2013 target board running the "blink LED" demo and are able to power it up using the TRF7960EVM from about 3 inches.  This used a simple half wave rectifier and 3V regulator.

    Best Regards,

    Eddie LaCost

  • 0 in reply to Eddie LaCost
    Prodigy 250 points

    Eddie,

    Thanks a lot for the information, it is good to know it will be pretty simple to get the field setup. Do you think using the typical application schematic in the datasheet/EVM would be sufficient for my implementation?  As far as my receiving circuit goes, space is very limited in my application so unfortunately I am using an 1812 sized off-the-shelf high-Q 3.9uH inductor with ceramic core as my receive coil, which I have found to need less than a few cm of proximity to receive much of anything, and that is just to get several volts rectified at a few hundred microamps. Thanks very  much again for all of the help and insight.


    Brennan

  • 0 in reply to dayberry
    TI__Mastermind 44220 points

    Brennan,

    I would recommend using the EVM schematic as is.  My thought is that you will need to change the impedance matching component values if you removed the RX lines which are not required for your application, but would not neccesarily reduce your component count.  You can also reference the TRF7960TB schematic if you would like to see something without a microcontroller.

    http://focus.ti.com/docs/toolsw/folders/print/trf7960tb.html

    One other thought... You could reduce the cost slightly by using the TRF7961 instead of 7960.  This is pin for pin compatible and the only difference is the ISO protocol handling supported.  Should make absolutely no difference for your application that is TX only.

    Best Regards,

    Eddie LaCost 

  • 0 in reply to Eddie LaCost
    TI__Guru* 91206 points

    Brennan -

    this is experiment we did that Eddie was referring to earlier - thought i would share here as it might be helpful

    6470.Deriving Voltage and Current from HF RFID_public.pdf

  • 0 in reply to Josh Wyatt
    Prodigy 10 points

    Hi,I am sps lokesh from india.This brief presents a standalone closed-loop wireless power transmission system that is built around a commercial off-the-shelf (COTS) radio-frequency identification (RFID) reader (TRF7960) operating at 13.56 MHz. It can be used for inductively powering implantable biomedical devices in a closed loop. Any changes in the distance and misalignment between transmitter and receiver coils in near-field wireless power transmission can cause a significant change in the received power, which can cause either a malfunction or excessive heat dissipation. RFID circuits are often used in an open loop. However, their back telemetry capability can be utilized to stabilize the received voltage on the implant. Our measurements showed that the delivered power to the transponder was maintained at 11.2 mW over a range of 0.5 to 2 cm, while the transmitter power consumption changed from 78 mW to 1.1 W. The closed-loop system can also oppose voltage variations as a result of sudden changes in the load current.

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