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ISO5451: driving HV MOSFET

Part Number: ISO5451
Other Parts Discussed in Thread: ISO5851

Hi, I am looking to use the ISO5451 (or similar) to drive a high voltage MOSFET (e.g. IXTF1N400) and I had the following questions:

1. What differences need to be taken care of when using the ISO5451 to drive a MOSFET instead of an IGBT? It is not completely clear from the datasheet.

2. My MOSFET will be connected as a "floating" high side switch (i.e. not ground referenced), is this possible with the ISO5451 please?

thanks

Nick

  • Hi Nick,

    Welcome to e2e, and thanks for your interest in our devices!

    I was a little surprised to see the IXYS part is 4000V!

    You probably want to be careful with the switching speed of such a high-voltage FET. If it switches too fast, the dv/dt might damage the driver.

    You can certainly use the ISO5451 as a high-side driver. The trick will be providing it with a power supply. You can use a bootstrap, or isolated supply to accomplish that. You may want to study this TI Design to see one recommended way to do it.

     

    If you have further questions, please let us know!

  • Hi Don

    Thanks for the quick reply.

    We are switching the device really slowly, in the order of seconds, and so hopefully the dv/dt should not damage the driver. But if you think it prudent to provide additional protection for the driver then please let me know about that.

    Yes, my plan was to use an isolated supply (either 18V or 24V) and connect it to the output driver supply pins (VCC2).

    Did you mean to include a URL or hyperlink for "this TI Design"? As I cannot see what you are referring to there.

    regards
    Nick
  • Hi Nick,

    Please refer to TI Design TIDA www.ti.com/.../tiduc70a.pdf. Please let us know of any questions.

    With Regards,
    Xiong
  • Hi Nick,

    Also refer to TIDA00195 for more info. www.ti.com/.../TIDA-00195

    With Regards,
    Xiong
  • Hi Xiong,

    Thank you for your reply.

    I had a few more questions please:

    - In my system, VDC_PLUS is 3 kV, is it OK for this driver IC?

    - Which points do I need to consider when using high voltage MOSFET, instead of IGBT?

    regards

    Nick

  • Hi Nick,

    1. We can do a better assessment on this point if you can share your schematic with us. ISO5851 can be a better options for systems with higher working voltage.

    2. In ISO5451/ISO5851, there is a under voltage lockout function for VCC2. The threshold is 12V. That said, the supply voltage of VCC2 needs to be higher than 12V in order for the driver to operate properly. We would recommend 15V min for more robust operations. Generally, MOSFETs switch at a higher speed than IGBTs. So precautions need to be taken on noise couplings when doing PCB layout.

    With Regards,

    Xiong

  •  Hi Xiong,

    Thank you for the reply.

    1. Please see attached sketch. We need to isolate the output of a high voltage power supply from a capacitor charging circuit, the maximum output voltage will be 3 kV and the average output current about 0.6 A. We plan to use a HV MOSFET, e.g. IXYS part number IXTF1N450

    2. We have an isolated power supply that is supplying VCC2, we have some flexibility in the voltage for that (e.g. 15V/18V/24V)

    regards

    Nick

  • Hi Nick,

    ISO5451/ISO5851 is not that suitable for your application where system voltage is 3kVDC. The limitations mainly lie on creepage and clearance distances of the package. Could you please show how the earth is connected in the system? Do you know what kind of isolation is needed for the gate driver? Basic, reinforced, or functional? We may be able to propose some discrete solutions (digital isolator + non-isolated gate driver) for you based on the isolation requirement. 

    With Regards,

    Xiong

  • Hi Xiong,

    Thank you for your email.

    We can add a cut-out slot in the PCB, under the IC, if that helps with the creepage distance? Or is this more to do with tracking across the body of the IC itself?

    The earth is connected to the negative terminal of the HV PSU, see below.

    regards

    Nick

  • Hi Nick,

    You are right that the creepage distance would be limited by the package of the driver IC. To support 3kVDC system, the min creepage distance needs to be 10mm. However, it is 8mm for ISO5851/ISO5451.

    In TI, we have digital isolators ISO7821DWW which can support system up to 3kVDC. Would a discrete solution of ISO7821DWW + low side driver work for you?

    With Regards,

    Xiong

  • Hi Xiong

    Agreed about the creepage distance, it's a shame larger packages with a wider body are not available.

    A discrete solution is fine, but we need to switch the high side, not the low side.

    Sounds like you might not have anything suitable?

    regards

    Nick

  • Hi Nick,

    Would you consider of using two isolation barrier in series to achieve higher isolation ratings? If yes, I would recommend you to use TI's ISO7821DW and ISO5852SDW in series. It is of worth mentioning that two isolated power supplies need to be used. I have also asked Jani to setup a call with you to make sure your concerns are addressed.

    With Regards,

    Xiong

  • Hi Xiong

    Thank you for your email.

    Would this solution support a working voltage of 3 kV?

    regards

    Nick

  • Hi Nick,

    Yes. It can support a working voltage of 3kV.

    With Regards,

    Xiong