current through FET
blanko
I am currently using this FET to toggle the power to a device. The
device wants 3.3V.
http://www.zetex.com/3.0/pdf/ZXM61P03F.pdf
I have pin 1 (gate) going to my microcontroller, pin 2(source) going
to a 3.3V regulator, and pin 3 (drain) goes to the device I am
powering. The 3.3V regulator can provide 800 mA of output current
and I need all of that going through the FET to the device I am
powering. The problem is that when I take a look at the datasheet
(page 5 , 2nd graph) I will only be getting a few hundred milliamps.
Does anyone have a different part they can recommend or an easy way to
modify my current setup to allow for a higher current?
Thanks!
-Mike
Adam S
You need a low gate drive P-FET. The above P-FET is really only useful
at Vgs above 4.5V. Such devices are not hard to come by.
http://www.zetex.com/3.0/3-3-2b.asp?rid=22
You are on the right track looking at page 5 , 2nd graph.
I'd imagine Farnell has an assortment on offer.
Jamie
Maybe i'm over looking something, I don't see a problem unless your
micro is not swinging to the rail?
What I would worry about how ever is switching time. if it's not
driving something at a constant pulse rate i think you should ok how
ever, if you are doing such a process, a Gate driver maybe in order
to force it on/off faster.
THat's just my opinion, that is why I like experimenting with
components before putting them in full use.
I will say how ever, Getting a lower (Ron) might be a better way to
go.. I kind of think that unit's on resistance for switching is kind of
high even at 0.35 ohms.
dfrombc
wrote:
Assuming configured like the switching time test circuit on the
datasheet....
Rdson = 0.35ohm...ok... Say 0.28V drop @ 800mA.
So load only gets ~3V @ 800mA
The transfer shows Id ~ 800mA @ Vgs ~ -2.0V.
Does that microcontroller output apply >-2.0Vouts with respect to the
source?
Notice the on resistance spec. When Vg= -5V then you get the 350ohm
Rdson. At Vg = -3V, it's a crappy 1 ohm or more.
Make sure Vg is right.
D from BC
British Columbia
Canada
Joerg
It is too weak and does not have a guaranteed Rdson at 3.3V, assuming
that's the gate swing you have available. Check out this one:
http://www.zetex.com/3.0/pdf/ZXM66P02N8.pdf
--
Regards, Joerg
Jamie
Joerg
The downside is that those cost around a Dollar in quantities. So if
this is for production I'd check the other sources such as IRF as well.
Jamie
IRF is usually what I use for things of this nature. (Logic Type Fets)..
--
"I'd rather have a bottle in front of me than a frontal lobotomy"
"Daily Thought:
SOME PEOPLE ARE LIKE SLINKIES. NOT REALLY GOOD FOR ANYTHING BUT
THEY BRING A SMILE TO YOUR FACE WHEN PUSHED DOWN THE STAIRS.
http://webpages.charter.net/jamie_5"
Joerg
> Joerg wrote:
>
>> Jamie wrote:
>>
>>> Joerg wrote:
>>>
>>>> blanko wrote:
>>>>
>>>>> I am currently using this FET to toggle the power to a device. The
>>>>> device wants 3.3V.
>>>>>
>>>>> http://www.zetex.com/3.0/pdf/ZXM61P03F.pdf
>>>>>
>>>>> I have pin 1 (gate) going to my microcontroller, pin 2(source) going
>>>>> to a 3.3V regulator, and pin 3 (drain) goes to the device I am
>>>>> powering. The 3.3V regulator can provide 800 mA of output current
>>>>> and I need all of that going through the FET to the device I am
>>>>> powering. The problem is that when I take a look at the datasheet
>>>>> (page 5 , 2nd graph) I will only be getting a few hundred milliamps.
>>>>>
>>>>> Does anyone have a different part they can recommend or an easy way to
>>>>> modify my current setup to allow for a higher current?
>>>>>
>>>>
>>>> It is too weak and does not have a guaranteed Rdson at 3.3V,
>>>> assuming that's the gate swing you have available. Check out this one:
>>>>
>>>> http://www.zetex.com/3.0/pdf/ZXM66P02N8.pdf
>>>>
>>> that's more like it! Got find :)
>>>
>>
>> The downside is that those cost around a Dollar in quantities. So if
>> this is for production I'd check the other sources such as IRF as well.
>>
> IRF is usually what I use for things of this nature. (Logic Type Fets)..
>
Same here. Best of all they let you sort by price. A quick twirl spit
this one out, under $0.20 in quantities:
http://www.irf.com/product-info/datasheets/data/irlml6402.pdf
JeffM
>[. . .]Make sure Vg is right.
(Completely OT)
Do you have a leading space in the username on your new account?
Google's archive is doing the strangest things with your posts.
On the front page of the group
http://groups.google.com/group/sci.electronics.design
you show up as "Anonymous".
Once the thread is opened,
http://groups.google.com/group/sci.electronics.design/browse_frm/thread/f48025bb1531284e/affbaced27828f80
your username disappears in the Thread frame
as well as in the Body frame
To see who posted, I have to click **More options**.
D from BC
wrote:
I checked, no leading space that I noticed.
And yeah, it's not looking pretty on Google groups..
I was set up ok before. Then my system needed to be redone and had to
reload all the software.
I've made some changes for this post..
Maybe I have it right.
D from BC
I put in my old 'spam this' email address.
Google groups is now appending to my usenet Google profile that goes
back more than a year.
'D from BC' shows up on the top line too for my posts.
Let me know if it's still fumbled.
JeffM
>>>(Completely OT)
>>>[...]Google's archive is doing the strangest things with your posts.
>>>[...]you show up as "Anonymous"[...]
>>>your username disappears in the Thread frame
> >>as well as in the Body frame
D from BC wrote:
>I put in my old 'spam this' email address.
>
That did it. Looking back, there was no email address listed.
That appears to be what made Google barf.