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ISO5451: iso5451

hailong xu1
Intellectual 260 points
Part Number: ISO5451

My application is single pulse for few mS, I think the desat function might not be able to use, could you please let me know the control signal timing for the inside MOSFET connected to DESAT pin?

Thanks,

Hailong Xu

  • 0
    TI__Expert 4875 points

    Hello Hailong,

    I'm an applications engineer in the high power drivers group.

    DESAT is only operational during the on-state of the switching device (IGBT or MOSFET). The first level of timing is the blanking time, which is set by your external capacitor based on the equation given in Section 10.2.2.8. This is the first delay, which is typically within the nanoseconds range because of the time it takes for the IGBT/MOSFET to turn on. What kind of device are you using?

    After the blanking time is complete, and the device has gone into desaturation then the DESAT fault is triggered as shown in the timing diagram of Figure 40. The timing specifications for DESAT are given in Table 7.10. The output will be driven low when DESAT is triggered based on the timing of t_desat(10%) to protect the system, which is defined as max 500ns. OUT is now held low. You are correct that the FAULT signal does take longer to transmit, at around 2us. However, you will not be able to turn on the device during this period of time after OUT has been pulled low, so the timing of t_desat(10%) should be sufficient to meet your timing requirements.

    If I was able to answer your question, please hit the green button!

    Thanks,
    Audrey

  • 0 in reply to Audrey Dearien7
    Intellectual 260 points
    Hi Audrey,

    Thanks for your information, but it might not get the point, maybe I did not describe clearly.
    in my application, The IGBT will be triggered by a pulse of 6mS long, if I'd like to utilize the function of DESAT, it might use a quite bigger cap tie to desat pin, I noticed that pin desat inside the IC tie to a diode and MOSFET;
    my question is:
    what kind signal is used to control the inside MOSFET, I guess when OUT is high, the MOSFET will off, then 500uA current will charge the cap
    connected to DESAT pin; is DESAT ramp in Fig. 40 from 500uA current source? or due to IGBT Vce?
    Thanks,

    Hailong Xu
    03/06/2019
  • 0 in reply to hailong xu1
    TI__Expert 4875 points
    Hi Hailong,

    The pulse of the IGBT, the 6ms you mentioned, does not make a difference with regards to the DESAT timing. You are correct that the internal MOSFET is off when OUT is high.To answer your question, yes, the capacitor and the 500uA current source are setting the DESAT ramp of Fig. 40. This time will set your minimum protection time for the DESAT pin to be clamped to the VCE.

    Does this answer your question?

    Thank you,
    Audrey
  • 0 in reply to Audrey Dearien7
    Intellectual 260 points

    Thanks, Audrey, It answers my question.

    Hailong Xu