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PMV31XN - dissipation?

Hi,

I'm trying to work out the maximum dissipation of an nxp (formally philips) part, the PMV31XN (otherwise known as beating your head against a brick wall!). I used the nxp support form and selected critical as this is holding me up, but I've yet to receive a reply 2 days later so its a good job is it only critical and not life and death isn't it :-/.

I have the PMV31XN data sheet, in that it says the part can dissipate

2W with Tsp at 25C and de-rates above that. Tsp stands for Temperature at the solder point. I'd guess that is the drain lead BUT the datasheet doesn't specify. It is also a not very helpful figure. Great if I attach and infinite heatsink to the drain lead I can dissipate 2W but I'm all out of infinite heatsinks so how about some practically useful figures, such as what can the part itself dissipate WITHOUT an infinite heatsink.

I'd assume somewhere in the range 200-500mW but where? And how do I calculate that if the datasheet does see fit to tell me nor can I find the data anywhere on the nxp web site. I'm considering replacing the part with some other manufacturer all because of the lack of data! When will manufacturers understand that good data is critical to sales. As is good and prompt support!

--

Malcolm

 Malcolm Reeves BSc CEng MIEE MIRSE, Full Circuit Ltd, Chippenham, UK
 (mreeves@fullcircuit.com, mreeves@fullcircuit.co.uk or mreeves@iee.org).
 Design Service for Analogue/Digital H/W & S/W Railway Signalling and Power
 electronics. More details plus freeware, Win95/98 DUN and Pspice tips, see:

 http://www.fullcircuit.com      or    http://www.fullcircuit.co.uk

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Reply to
Malcolm Reeves
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Hi Malcolm

The thermal resistance of the part is 60C/W at DC to the pins. At 25C starting, then the junction will be at 145C for 2W dissipation, just within it's limits.

Of course, this will raise the temperature at the pins (by how much depends on the thermal resistance of the board. Assuming these are fairly small tracks (it's a SOT23 after all) I'll assume theta Track-ambient of 40C/W. That's a total of 100C/W junction to ambient - in other words we can convert the problem from junction to pin to junction to ambient.

I would not personally run the part higher than 0.5W - at that, I would expect a junction rise of about 50C from ambient and the pins will be at about 20C above ambient (derating the part anyway).

Interesting that they don't show theta j-a (via the case) at all. Knowing Philips (sorry, NXP) all that information will be in a separate data sheet somewhere that they just expect you to know how to find.

If I felt less lazy I'd throw a spreadsheet together to show the limiting conditions for the device, but it's Friday and I've hda a full day of designing for a new board, so I going to sit with some wine :)

Cheers

PeteS

Reply to
PeteS

I almost feel your pain. Back in the good old days of chunky packages and stuff..... It's not as if you had problems dealing with that.

Anyway... Like PeteS says things haven't changed so much so, if you've been doing this for a bit then you'll see that the headline data is the similar lies and all have to do is move your POV camera to the drain pin and work out the properties of what's heatsinking it.

Oh..... shit!!!!!

I feel your pain....... and I don't really believe that PeteS is going to knock up a spreadshit to do it...... or maybe he can..... If he can and provides the supporting information to prove it then it will be worth your money.

DNA

Reply to
Genome

I am not sure if I should feel honoured or soiled by your faux adulation ;)

I'll knock up a quick spreadsheet tomorrow (when I am not under the affluence of inkerhol)

Cheers!

PeteS

Reply to
PeteS

Bonus!!!!

Don't tell me nuffink.

If Malcolm is happy I'll sort another bottle of wine.

Where there's a will there's a way... I mean sorting out the wine thing.

DNA

Reply to
Genome

Well, I have been drinking a very fine wine tonight (actually *two* very fine wines) so I am in no shape to do such calculations now ;)

I have lots of willpower, but sometimes I seem to lack won't power

Cheers

PeteS

Reply to
PeteS

Yeah yeah yeah. So you're a hero. I'm up to 33 units on the Cider label already and have my lottery tickets for tomorrow because I forgot it was Friday. In case you forgot you're going to do a spreadshit that does all of that shit anyway.

No f*ck it..... go cuddle your bed, and whatever might be in it. I'd kick the bitch out and get a cat.

Barp!!!

Time to make bread wiv onions in it... I think.

Are you trying to be a tart?

DNA

Reply to
Genome

The assumption is the critical bit. What I looking for I guess (besides venting my spleen about poor data sheet and poorer support!) is some philips data reference or someone else's data to work out pin to ambient.

I'd worked out that theta j-p is 62.5C/W ((150C-25C)/2W). Why they didn't just say that I don't know. It's not helpful to hide the figures and the graph of power is just a waste of ink. It would be more useful, as I seen on other parts, philips ones included, to quote j-a and j-pin. That way if you need to get more out of the part you can add copper and do more extensive calculations. If it works with j-a then you don't need to do the calcs even if you add the copper).

It all comes down to needing a nxp figure for j-a for nxp sot23 package and/or some data for PCB copper area C/W to ambient.

Malcolm

Reply to
Malcolm Reeves

I agree with you.

NXP (Philips in an even less useable guise as far their website is concerned, and *that's saying something*) has been notorious for not providing relevant details in the standard data sheets.

I'll have to dig back at work, but I seem to remember one Philips part where the package diagram, thermal response tables and even pinouts were in 3 separate datasheets apart from the core datasheet.

This is of interest in another way; I am probably going to move to an ARM7 device on a major device redesign, and Philips has parts, but if the docs are still going to be like this, I won't touch it. I don't care how damn good the part is, if it's not documented so I can design

*easily* with it, I won't use it.

Cheers

PeteS

Reply to
PeteS

I don't have to try. I spent 12 years in the Royal Navy (ended up as a Chief) and they *train* us to be tarts.

Cheers

PeteS

Reply to
PeteS

NXP have replied and it is a classic. I though the spice model situation was poor enough but this takes the biscuit. Apparently if I had flotherm they could give me a similar part model that would get me close. So it is impossible then to do a quick back of fag packet calculation to see if the part is likely even to be suitable! I have to model the entire system on flotherm just to find out!

If I had flotherm I'd certainly want to estimate what the results would be and not blindly rely on the results.

Why is it that we seemed to manage in the past with datasheet figures, and other manufacturers supply them but for nxp with need flotherm and a model (which they don't have anyway!).

Just venting my spleen I guess.

Reply to
Malcolm Reeves

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