Looking for P-Channel High-Side MOSFET

[Mr.RC-CAM]

I am designing a 500Hz motor speed control that needs a high side P-Channel MOSFET switch (sorry, but the favored N-Channel will not work for me). So, what is a good Digi-Key sourced part that will allow 5V logic switching and can handle 12 Amps? I need .05 ohm RDS or lower.

I definately do not want something that needs an external charge pump for good turn-on. Logic level switching (from a PIC) is wanted. I don't mind using a buffer, but prefer to skip it too. What has worked good for you?

RC-CAM

[jeffs555]

I haven't used either of them, but only saw two at digikey that would fit your requirements, IRL5602S and MTP50P03HDL. They both have rather high total gate charge, but at 500Hz, the switching losses will probably be small, even with switching times of several microseconds. Unless your motor voltage is 5v or less you will need a high voltage driver, and a simple npn transistor driver with pullup will probably do at your low switching rate.

[Mr.RC-CAM]

Thanks for the recommendations. I will check them out. I have some high voltage driver IC's, so that part is covered.

RC-CAM

[zagisrule!]

I think that Onsemi had quite a few logic-level devices that would be perfect for this application in the TO-252 package.



-Matt

[tve]

never mind, the part I thought would work wont... sorry.

[Nightz]

Infinion has a few logic level P-Channel Parts. Not sure if digikey distrubutes for them or not.

-Rocko

[Zlatko]

Hi,
IRF7410
http://www.irf.com/product-info/datasheets/data/irf7410.pdf
20V max ( 12V continuous ), 16A continuous ,SO-8 Pack, 0.007 Ohms at Vgs = -4.5V
Cheers

[Mr.RC-CAM]

The IRF7410 looks mighty fine. I'll order some. Thanks!

RC-CAM

[jeffs555]

That is a good choice, but one problem to watch for with the IRF7410 is its 8volt max Vgs. If your motor voltage is higher than this, you will need to have a zener or some other way to limit the gate drive voltage, so you don't destroy the mosfet.

[tve]

That is a good choice, but one problem to watch for with the IRF7410 is its 8volt max Vgs. If your motor voltage is higher than this, you will need to have a zener or some other way to limit the gate drive voltage, so you don't destroy the mosfet.

Yup, I blew up a few of these!

[Mr.RC-CAM]

It will be powered by 8.5VDC. From the data sheet, it looks like I can simplify the interface and use a 5V logic level (directly from a PIC) on the gate. The load is a motor, so it is inductive. Where should the zener be placed for full protection?

RC-CAM

[jeffs555]

You can't use a 5v logic level to drive the gate because in order for the P-channel mosfet to turn off, the gate needs to be pulled up to the motor supply voltage which is too high for an output from a pic. With your low switching rate, you can use a simple npn transistor like the attached circuit. Since R1 and R2 form a voltage divider, as long as the supply voltage is limited to 8.5v the voltage drop across R2 won't be more than 8 volts, and you could do away with the zener.

[Mr.RC-CAM]

I understand. I'll revert back to using the high voltage buffer, but will toss in the gate clamp zener too.

RC-CAM

[Comatose]

On most PICs one of the pins is an open-collector output which can go as high as 14v without damage. This is usually pin RA4. (it doesn't exist on the pic12 family, but most of your pic16s have it. Check your datasheet) Using that you could do away with Q1, R3 and R4 in jeffS555's schematic.

Goint to a FET with a higher gate voltage would obviate the need for the rest of the circuit save a pull-up resistor. IRF7425 would be a good choice. 8 milliohms, rated at 15A, in so-8 with a max VGS of +-12.

[Dan Baldwin]

I've been using the STP80PF55 for a high side fet. It has low RDS on (.016 typ), and low turn on voltage. I don't have a Digi-Key part number, but the Mouser PN is 511-STP80PF55

Data sheet;
http://www.st.com/stonline/books/pdf/docs/8177.pdf

Dan

[jeffs555]

Comatose,
That is really interesting. I have been mainly using AVR's instead of PIC's, but that may be a reason to give PIC's a try again.

Jeff

[Mr.RC-CAM]

On most PICs one of the pins is an open-collector output ...
I am familiar with that feature. But, it is suppose to be protected with an ESD diode that will effectively clamp its input to Vcc. Are you sure it can be pulled higher without damage?


IRF7425 would be a good choice.
That sounds like the best choice for me yet. Thanks.

RC-CAM

[Comatose]

According to the datasheet, protection diode on RA4 is to VSS only, at least on the 877A. I've not used the feature on other pics, but it should be the same. Protecting the pin with a 10v zener is a good idea, but you can safely use it to drive your FET.

[Mr.RC-CAM]

According to the datasheet, protection diode on RA4 is to VSS only, at least on the 877A.
That is good information to know. However, it might be a little too close for me. The F87x data sheet says RA4 is good to +8.5VDC max. Not that it will help me, but MCLR is good to +14VDC Max.

Thanks for the info.

RC-CAM

[Comatose]

Hrmmm, so it does. The pic16f7x7 datasheet claims 0 to 12v though, and so does the pic16f7X line. Anyway, hope that helps.

[jeffs555]

They all seem to have different specs for the RA4 voltage, and their selection guides don't have that as a parameter, so you just have to wade thru the data sheets. The 16f627,628,648 spec 14v on RA4 which would provide a comfortable margin.