Re: How to interpret this package drawing?

On 5 May 2007 13:11:39 -0700, the renowned Michael
<nleahcim@xxxxxxxxx> wrote:

On May 5, 2:56 pm, John Larkin
<jjlar...@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
On Sat, 05 May 2007 14:46:41 -0500, John Fields

<jfie...@xxxxxxxxxxxxxxxxxxxxx> wrote:
On 5 May 2007 12:18:49 -0700, Michael <nleah...@xxxxxxxxx> wrote:

Hi - I'm trying to draw out a TO-263-5 from this data***:
http://www.irf.com/product-info/datasheets/data/iru1150.pdf

Thing is - it doesn't actually give dimensions - just minimum and
maximum dimensions. It doesn't even specify the actual width!! What am
I supposed to do here? Take the average of each value?

---
Yup, and set your tolerances so they fall within the minimums and
maximums. :-)

What's stunning is that the nominal lead pitch is not specified. So if
you guess or average to get the pitch, any error stacks up over all 5
pins! So get a sample and measure it.

That's what really caught my eye. It's ridiculous - I've never seen
such a bad drawing. I got something hacked together that should work
though, by averaging all the values.

I found another company's drawing for TO-263-5s and they specified the
pitch as 1.7mm, which is essentially the average of the min and max
values (1.702mm).

It's also the same as IRF's drawing for the TO-262 (1.700 mm nominal),
as you can see from this package drawing:

http://www.irf.com/package/cic/5pto262po.pdf

It's laid out with proper GD&T tolerancing-- the numbers in boxes are
"basic" dimensions that are theoretically exact, and the position of
each lead is defined off the 'A' datum in the maximum material
condition so you can easily figure worst case conditions.

It would be tempting to guess that the nominal dimension is the same
as the SDIP pitch of 1.778mm nominal (0.070"), but it'snot.


And the compensation/stability guidelines suck, as is standard for
LDOs. The "Stability" paragraph is just qualitative blather.

I wouldn't use this part unless I absolutely had to.

I'm saving a decent amount of money going with this part though, so
the extra hassle is worth it, I hope. I don't need a particularly
smooth supply - I just need an adjustable vreg capable of taking a 5V
signal down to 3-3.5 V (adjustable) with ~200mv or less ripple, all at
about 2-3A. (constant load)

-Michael


Best regards,
Spehro Pefhany
--
"it's the network..." "The Journey is the reward"
speff@xxxxxxxxxxxx Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com
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