Hi again,

I have what seems to be a fairly simple question regarding the selection of a high side switch. Here is some helpful info:

My signal is a 0-3.3V PWM signal from a microcontroller, and I'm looking to control a proportional valve with a max load current less than 3 amps (inductive load). Normally, I would use an N-channel MOSFET with a flyback diode and snubber circuit, but I'm limited to high side switching with this application. My initial thought was to use a P-Channel MOSFET, but I came across some nifty devices that seem like they might work for my application. One example would be the ITS428 from Infineon. If I used this device, it seems like I wouldn't need to use a MOSFET driver or a snubber circuit, which would be nice.

Does anyone have experience with these devices? If so, would it work for my application? I'm going to contact Infineon as well and see what they have to say. Thanks in advance.

John

 

No experience with them, but they look interesting.
Datasheet: http://www.infineon.com/dgdl/ITS428...7155f&fileId=db3a30431c69a49d011cdcc9a1fd41df
One item might be problematic; that's the turn-on threshold voltage. Typical is 1.7v which is fine, but the max being 3.2v makes it mighty close with your 3.3v output from your uC.

 

I noticed that too, and it might be a problem. I'm going to order some anyways and give them a shot. My uC outputs slightly less than 3.3 V (it's closer to 3). Could I clamp my uC output to say 3v with a zener diode to stay below that 3.2v just to be safe? Any thoughts?

 

The problem is that you might have to get the input above 3.2v in order for it to consider that to be a logic "1". If your uC output is only 3v with no load, then there is a chance that it will not work due to the stated specifications.

If you tried clamping the uC output to 3v, you would simply make the problem much worse.

 

Oh I was thinking of it as I couldn't exceed the max rating of 3.2v. I figured as long as it's between the minimum (1.7v) and maximum (3.2v) it would be okay. But now I see that it's saying it could regard UP TO 3.2v as logic 1.

Hopefully that maximum isn't the case with the ones I order . I'll get them in next week and let you know what happens and what I destroy. Thanks for the help.

 

You still don't quite have the idea.

The threshold for it to recognize the input as a logic 1 can be anywhere from 1.7v to a maximum of 3.2v. That means you will have to exceed 3.2v in order to be guaranteed that you have told the device to turn it on. Your mileage can (and will) vary.

 

Reading back over my previous post, my grammar was a bit off. We're on the same page

 

Update:

I've found something that may work a bit better.
Datasheet: http://www.infineon.com/dgdl/BSP762...04103&fileId=db3a304412b407950112b4297a384104

I forgot to mention also that this is a 24V application. I'll try to get some scope captures up next week for people wondering if these work well in the place of a PMOS high side MOSFET switch for inductive loads.

Thanks again SgtWookie.