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TIDA-00637: GFCI Detection Question

GaryC
Intellectual 2315 points
Part Number: TIDA-00637
Other Parts Discussed in Thread: LM7321

We are working on 240V EV for US standard. This design need to implement J1172 compliant. We have refer to TIDA-00637 design, and have some question about metering and GFCI design.

  1. Can the GFCI section of the line detect the 4-6mA leakage current? Whether the smooth DC current can be detected ?
  2. What is the response time when the GFCI fault is triggered?
  3. The LM7321 is used to the GFCI detection. May I know it has any spec need on this design? Do we have other alterative solution to suggestion.
  4. Could you share the spec of GFCI CT configuration(Figure 15)? Or you have guideline to design this CT.

BR Gary

  • 0
    TI__Intellectual 2315 points

    Sorry for pushing you. Do you have any recommend for the questions? Thanks

    BR, Gary

  • 0 in reply to GaryC
    TI__Expert 5670 points

    Hi Gary,

    I can help with answering some of the questions now and will need to look into a some in more detail and get back to you later today.

    1. Can the GFCI section of the line detect the 4-6mA leakage current?
      1. This will depend on the sensor but AC detection is typically around 20-30mA RMS.  For DC detection of 4-6mA  that would need to be additional circuitry to enable DC detection as CTs are typically used for AC detection only. 
    2. Whether the smooth DC current can be detected ?
      1. With the current circuit on the TIDA-00637, it is intended to detect AC faults only.  We are working on a design that enables smooth DC detection and I can send you the current slide deck that shows the architecture and devices used for a flux gate topology.
    3. What is the response time when the GFCI fault is triggered?
      1. I will need to look into this to see how fast the interrupt executes and switches off the relay.
    4. The LM7321 is used to the GFCI detection. May I know it has any spec need on this design? Do we have other alterative solution to suggestion.
      1. On this design the diode in the feedback loop is being used as a peak detector circuit.   In the slide deck I will send it goes over a couple of ways for AC detection using either a peak detector or a full wave rectifier circuit.  For op amp specifications,  some important ones are bandwidth and SR to be able to track the response quickly.  Depending on the customer's specifications there may be multiple trip points based on different fault frequencies.  
    5. Could you share the spec of GFCI CT configuration(Figure 15)? Or you have guideline to design this CT.
      1. For the GFCI CT configuration in Figure 15 I will need to look into this to see what guidelines were used for the CT in this reference design.

    Let me know if you have any questions on the current answers and I will send the slide deck for the DC solution shortly.

    Best regards,

    Errol

  • 0 in reply to Errol Leon6
    TI__Expert 5670 points

    Hi Gary,

    Could you send me your email address so I can send the presentation?

    Best regards,

    Errol