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TIDM-02006: Question regarding comm. and position loop speed

Yiu Hang Li
Intellectual 460 points
Part Number: TIDM-02006

Hi there,

We have just start looking into reference design TIDM-02006 and have some questions regarding its manual (TIDUEV1):

1. Referring to figure 9, with FSI, what is the max. possible comm. frequency between position and speed controller and each inverter? We will need at least 8kHz

2. With this design, what is the max. EtherCAT PDO cycle it can handle? 

3. What is the max. possible frequency of each position loop (referring to figure 9) running in F2838xD?

4. For "Communication cycle time" in table 1, is it talking about EtherCAT or FSI?

Thanks for reading, any reply is appreciated.

  • 0
    TI__Guru** 109740 points

    1. That depends on the length of the frame data and the number of the slave node. In this reference design, 8kHz can be supported for 2~3 nodes.

    2. No tested benchmark, that depends on EtherCAT master since the EtherCAT is handled by the CM3 core.

    3. As Q1, and is related to the frequency of the current and speed loop frequency you used.

    4. Only for FSI. We don't test EtherCAT data in this reference design. 

  • 0 in reply to Yanming Luo
    Intellectual 460 points

    Thanks for the informative reply Yanming!

    2 more questions:

    1. In table1 entry "Switching PWM frequency", it is stated the max. PWM can reach 40kHz. If we did use 40kHz in our application, is there enough CPU time left to handle 8kHz FSI comm.?

    2. If FSI comm. frame data word reduce to 3words (e.g. only transmit pos. cmd), can the design support more inverter? Is there a formula to estimate?

  • 0 in reply to Yiu Hang Li
    TI__Guru** 109740 points

    1. That depends on the execution time of the ISR for motor drive and FSI. In some cases, you might apply the PWM frequency is not equal to the control frequency. 

    2. As replied to Q1. Case by case, you might calculate the ISR, TX, RX time based on the CPU and FSI clock frequency.

  • 0 in reply to Yanming Luo
    Intellectual 460 points

    Thx for the anwsers Yanming