Review.IT – When apples ain’t apples!

Further to my reprogramming of the BIOS for my HP EliteBook 2530p, I did some further research since I generally research things before I order bits from eBay.

The Atmel AT26DF321-SU chip used for the BIOS in the HP EliteBook 2530p is in fact a SOIC-8 package – however, it is based on the EIAJ standard which was 5.2mm across the body when I measured it with my digital caliper. The other standard is JEDEC which measures 3.9mm across the body when I measured some other SOIC-8 chips. In actual fact SOIC and SOP are often taken to be the same package.

Now, here is when it gets a bit confusing. SOIC packaging refers to pin spacing of 1.27mm however SOP is supposed to be for less than 1.27mm pin spacing – understand? If you were to design printed circuit boards, you will often need to actually obtain the components in order to do so, or have to go through tons of datasheets to verify package sizes – correct? Actually, not so – most people would use software that would pick up these details when you choose the part number of the item you are placing on the circuit board, so a SOIC-8 package should be the right one, or is it?

My research has shown that the standard JEDEC SOIC-8 package would be about 3.9mm across the body. The EIAJ SOIC-8 package would be about 5.4mm across the body. For higher pin counts, like SOIC-16, there is actually a package that is 7.5mm across the body. The good thing is that the pin spacing is the same – at 1.27mm for SOIC.

I found also that there is a mini-SOIC or sometimes called a micro-SOIC that has pin spacing of 0.5mm, so be careful of what you are actually seeing – don’t just pick up on the SOIC and assume 1.27mm pin spacing.

Interestingly enough, the datasheet for the Atmel AT26DF321-SU also refers to the chip as being a plastic small outline package, or PSOP.

Anyway, the chip adapter socket that I bought is actually for SOIC-8 and SOP-8 when referring to the JEDEC package and for 1.27mm pin spacing. I just couldn’t use it for my chip because I needed a EIAJ socket – oh well, at least I can use it for other SOIC-8 chips. This means that I didn’t actually buy the wrong adapter socket, just didn’t read the Atmel datasheet fine print sufficiently.


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