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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.
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
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 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