Mosfet Driver

[Lord_grezington]

Hi

I have tried posting a similar post on the microchip forum, but due to no response and VERY POOR user friendliness I have decided to change the component to a similar one and put it on here instead...

I am hoping to use http://www.ti.com/litv/SNOSAW2M which I think will work well in the application.

But, I am looking to use the top side drive completely separate to the low side. Ie HS is connected to the high side source mosfet, but is not connected to the low side drain. Each circuit will be independently controlled for completely different applications.

I expect Steve has a good answer to this, but I will accept any intelligent response.

thanks

 

[KrisBlueNZ]

I don't know what part number you're planning to use, and the link goes to a 404 error. But in general, you'll probably have trouble because of the logic inside the driver that's designed to prevent simultaneous activation of the high-side and low-side MOSFET. The driver even enforces a short delay between one turning OFF and the other being allowed to turn ON, to prevent shoot-through currents due to switching delays in the MOSFETs. So you won't be able to control the high-side and low-side outputs completely independently; the driver will not allow both to be enabled at the same time.

 

[(*steve*)]

Your link appears broken. Are you looking for a high side driver?

 

[Lord_grezington]

Sorry, here is the link again.
http://www.farnell.com/datasheets/89488.pdf

 

[KrisBlueNZ]

That data sheet is for the LM5100A and LM5101A.

According to the block diagram, there is no connection between the high-side and low-side drivers, so I expect you can use them independently.

Remember that the source connection for the high-side MOSFET needs to be switching constantly so that the charge pump will operate.

 

[Lord_grezington]

Thanks Kris

Any idea what the duty cycle needs to be to ensure it keeps switching? I was just going to use trial and error when I get the board made but it would be useful if we can work it out. The bootstrap capacitor will be 0.33uF.

Thanks

 

[KrisBlueNZ]

The data sheet doesn't have any guidelines, and there's not enough information there to be sure. It will also depend on the switching frequency. My gut feeling is that any duty cycle in the range 2%~98% would probably work; anything in the range 5%~95% would definitely work. Like you, I would test a prototype, under full load and with simulated extra loading, to be sure.