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AFE4300

Mastro
Prodigy 110 points
Other Parts Discussed in Thread: AFE4300

Hello,

I am interested in using the AFE4300 for impedance measurements. I am not interested in its weight scale measurement capabilities.

I want to built a custom board with as few components as possible. I have been looking on your reference designs tidr119 and tidra02, which are essentially the same with regards to the implementation of the AFE4300.

I need to use this for tetrapolar measurements.

1. Can I connect the two current electrodes to any two pins between 22-27 and the two voltage measurement electrodes to any two pins between 33-38?

2. Do I need the 10M Resistors you have in tidra02 between pairs of Iout pins (R-67-63)?Do I need all of them?What is their purpose?

3. Do I need the calibration or can I get away with it and leave pins 28-31 floating?

4. What is the smallest current I can inject? Can I set this with the resistor connected between pin 20 and the capacitor on pin 19? Is it controlled by the SPI? 

5. What is the highest frequency I can measure impedances with? 100kHz? 150kHz? 250kHz?

6. What is the best way to choose the gain resistor?

7. Can you send me code for an MSP430 to communicate with the AFE4300 and control the impedance measurent part of the chip?

Thank you,

Mastro

  • 0
    TI__Expert 6320 points

    Mastro,

    We have received your post and will be replying shortly.

    Thanks,

    Chuck Smyth

  • 0 in reply to Chuck Smyth
    Prodigy 110 points

    Hi Chuck,

    I have a couple more questions that I forgot about.

    8. Depending on your answer to 1 in my previous post, Do I leave unconnected Iout and Vsense pins floating?

    9. In tidra02 you have capacitors (C15-C20) connected to the Vsense pins 33-38 and to the Iou pins 22-27 (C24-C26 and C39-C41). Do I need all of them or should I keep them only to the Vsense and Iout pins I will use. What is their purpose?

    Looking forward to your replies.

    Thank you

  • 0
    Intellectual 350 points

    Hi Mastro,

    I'm also awaiting responses to many of your questions as well but I did find in "5023.afe4300 FAQ.docx" this for question #5

    "

    Q:What is the accuracy measurement when using 250 kHz (maximum attainable frequency) and 80 kHz as the source signal frequency?

    R:There is a low-pass filter after the DAC with a cutoff frequency of 150 kHz +/- 30 kHz. So, to keep the signal from attenuating we made the max excitation frequency to be 80 kHz.

    After calibration you can get an accuracy of 1%.

    "

    Marty

  • 0 in reply to MARTY steinDORF
    Prodigy 110 points

    Hi Marty,

    Thank you very much for your reply. The Data sheet mentions 150kHz and the white paper they link on their website (Minimal implementation of an AFE4300-based spectrometer for electrical impedance spectroscopy measurements, B. Sanchez et al) reports measurements with the AFE4300 up to 100kHz (if I interpreted the document correctly).

    Is it possible that this FAQ doc describes the Evaluation Board capabilities?

    Thanx,

    Mastro.

  • 0 in reply to Mastro
    TI__Mastermind 18285 points
    Mastro,

    1. Yes, as long as you setup the GUI properly.

    2. Answered in this post: e2e.ti.com/.../425106

    3. I would recommend using calibration.

    4. A small current on the order of 1-10 µA can be passed between two electrodes(< 800 µA). There are many articles and resources out there on the web that you can research to learn more about this measurement.

    5. 80kHz, Page 4 of the datasheet shows a -3dB bandwidth of 150kHz +/- 30kHz, but this is a typical value so the max we say is 80kHz

    6. Which gain resistor are you referring to? If you are referring to R and 2R in Figure 8, then those are fixed.

    7. Our firmware source code can be found on our product folder. www.ti.com/.../toolssoftware
  • 0 in reply to Amy Schnoor
    Prodigy 110 points
    Thank you Amy very much for your response.

    1. Do I leave unconnected Iout and Vsense pins floating? I will not be connecting any resistors and capacitors to the unused Iout and Vout pins. Is that OK?

    2. So no more 10MR between Iout pins and use rather a 10kR in parallel with the 1uF capacitors.

    3. OK use calibration, but capacitors to the V-recording calibration terminals are not required, only a 1uF and a 10kR in parallel at each I-calibration terminal.

    4. Apologies for repeating my self, but can I set the stimulus current with an additional external resistor connected between pin 20 and the capacitor on pin 19 and using Equation 5 of the data sheet?

    5. OK. 80kHz.

    6. I am referring to the external resistor that needs to be connected between pins 7 and 8.

    Thanking you in advance,

    Mastro.
  • 0 in reply to Mastro
    TI__Mastermind 18285 points
    Mastro,

    1. I would not leave the pins floating because there could be some impedance on the lines. I would ground it if they're not used.

    4. We set a 0 ohm resistor there just in case.

    6. We use a potentiometer so we can adjust this value as needed. You can start out with that then once you have the value you need, you can switch it out.
  • 0 in reply to Amy Schnoor
    Intellectual 350 points

    Hi Mastro,

    6: From what I can tell, this Rs resistor only affects the WT front end which you are not using.  I do not think it has any affect on the impedance subsystem.  I would not remove it or things may rail but I don't think you care what value it is. I would select a high value ==low gain Rs in your case.