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I have seen several high-side MOSFET drivers which are internally isolated. As I can understand, isolated gate driving is a fairly new technology, since they encapsulate all the complexity in a single chip.

One such driver is the ADuM3322x (thanks to comment below), which is an isolated 4A Dual-Channel Gate Driver, designed to drive N-channel MOSFETs:

enter image description here

In the datasheet it is stated that,

The ADuM3220/ADuM3221 digital isolators require no exter-nal interface circuitry for the logic interfaces.

If this driver is indeed intended to drive a high-side MOSFET, there needs to be an added bootstrap circuitry, which I couldn't find any mention of in the datasheet, unless it does not even require the bootstrap circuitry.

As explained here,

You must drive the MOSFET between its gate and source terminals. Since the source terminal voltage of a high side MOSFET will be floating, you need a separate voltage supply (VBS: VBoot Strap) for the gate drive circuit.

I cannot understand how this circuit provides the needed voltage to power the MOSFET.

My first question is: How can this particular driver actually drive the high-side MOSFET?

Followed by: If this requires additional bootstrap circuitry, are there isolated high-side drivers which come with in-built DC-DC converters?

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You can use parts in this series with a boot-strap capacitor and diode as shown on page 16 of this datasheet.

http://www.analog.com/media/en/technical-documentation/data-sheets/ADuM3223_4223.pdf

You could also use this part with an isolated power supply such as the ADUM5000.

http://www.analog.com/media/en/technical-documentation/data-sheets/ADuM5000.pdf

Analog devices also makes isolated gate drivers with integrated isolated power such as...

ADUM6132

http://www.analog.com/media/en/technical-documentation/data-sheets/ADuM6132.pdf

ADUM5230

http://www.analog.com/media/en/technical-documentation/data-sheets/ADuM5230.pdf

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  • \$\begingroup\$ Thanks, these are excellent suggestions. Thinking of going with the ADUM5230. Internal isolation and on-chip DC-DC converter. Looks relatively simple to connect as well. \$\endgroup\$ – Rrz0 Apr 9 '18 at 18:52
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This particular device simply performs the logic level translation and isolation for you. It does not do the floating supply generation.

As your second quote indicates, you need to supply the driver side with the right voltage supply in order for it to function as you expect it to. That means, if you want to drive high side N-Channel MOSFETS you need to provide your own floating supply circuit that generates the appropriate voltages between GND2 and Vdd2.

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  • \$\begingroup\$ I see, so one would need to calculate the values for the capacitor and diode if a bootstrap circuit was used. Is it possible for this to be in-built (I cannot find any datasheet even though I have read that they are available). \$\endgroup\$ – Rrz0 Apr 9 '18 at 17:35
  • \$\begingroup\$ @Rrz0 there are a number of them but I forget the numbers. Search on here, you will find some. \$\endgroup\$ – Trevor_G Apr 9 '18 at 17:38
  • \$\begingroup\$ Thanks. This answers my original question. My last followup question is whether the schematic above would be suitable to drive one single MOSFET. Even though it has 2 inputs and 2 outputs, they are completely separated from each other. \$\endgroup\$ – Rrz0 Apr 9 '18 at 17:40
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    \$\begingroup\$ @Rrz0 the 3221 allows them to be fully independent. \$\endgroup\$ – Trevor_G Apr 9 '18 at 17:43

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