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TMP107 based sensor system front end esd protection setup

David Nyarko
Expert 1575 points
Other Parts Discussed in Thread: TMP107

I am currently evaluating a 4 sensor TMP107 system setup using a PIC18F microcontroller with a buffer connection to the 1st sensor as in section 8.2.1 (Figure 39. Connecting Multiple Devices) of the TMP107 document , SBOS716B -MAY 2015 - REVISED SEPTEMBER 2015 . The setup and processor are running off 3.3V.

In another TI document, the Application Report SBOA138A ( Easy-to-use Cabling Interface for Measuring Temperature with the TMP107). It is indicated in section 2.8 (page 8) that the resistor R3 (100 ohm)  in Figure 6 (Examples USB Port-Based Control Board) is for ESD current limiting and glitch attenuation . 

- Is the above mentioned ESD function similar to that in my setup mentioned earlier, and also will this be enough to protect against possible overvoltages?

- If not,  any suggestions (e.g. diode based) for a suitable esd protection setup at the input (I/O1 - pin 3) of the 1st sensor in the daisy chain which will not affect the system performance?

Thanks

  • 0
    TI__Mastermind 31600 points
    Hi David,

    Let me review and get back to you.

    Aaron
  • 0 in reply to Aaron Heng
    TI__Mastermind 31600 points
    Hi David,

    I reviewed the application report that you mentioned above. In my opinion, the resistors are there in series with the transmits line (Rx, Tx) is acted like a termination and current limiting. It helps to absorb any reflection.

    It also help to protect amount of current flowing in or out (sink or source) preventing damage the device, which I doubted about it since the series resistor is very small. This incident is sometimes end user might accidentally program the firmware conflict with the pin type input/output.

    If you are concerning about the overvoltage, I would suggest to place a diode clipping at the power supply pin where it can provide overvoltage protection from exceeding the voltage level of 3.3V.

    Placing the diode on the transmit line might create a distortion effects, so I wouldn't suggest to do that.

    I will confirm this after the Thanksgiving holiday with my colleague since he wrote the report.

    Have a nice Thanksgiving!

    Aaron
  • 0 in reply to Aaron Heng
    Expert 1575 points

    Aaron,
    Thanks. I will await your response next week.
    Have a great Thanksgiving.
    David

  • 0 in reply to David Nyarko
    TI__Mastermind 31600 points
    Hi David,

    The above comments are correct, and here are more comments after I spoke with my colleague. The TMP107 can drive a very high current around 45mA, and to prevent from damaging the MCU Rx and Tx. The resistor in series is in place to protect Rx and Tx pins. Since TMP107 can be configured as a daisy chain, and wire can be long distance, the resistor in series to help reducing any sharp spikes or glitches when it is in noisy environment. It also prevents any over voltage occur.

    Aaron
  • 0 in reply to Aaron Heng
    Expert 1575 points

    Aaron

    Thanks.