difference between SOP and DIP? Bad batch of chips?!

Thread Starter

pgo1

Joined Nov 7, 2012
48
Im currently transferring an existing design from through hole to surface mount. i got some boards back and made one up, and found the DAC (DAC0800LCM) was overheating. i looked over and over a the circuit and could see no mistake. The original works fine, this one is the layout. I removed the chip out and looked at what was on all the pins - they all looked fine. i measured the resistances between all the pins and ground / power rails blah blah. I eventually put the DAC in and bent all the input pins out so they didn't connect, but left all the rest in - hey presto! No overheating.

I went through one by one and found the culprit - pin 7, input 3. I couldn't see anything untoward about this pin - no shorts on the soldering, no defects on the boards. I removed all connections so it was only connecting to the shift register which drives it - still overheating. This shift register drives all the input pins, so probably not an issue there... I disconnected the pin entirely and measured it to find something odd - it settles at the negative rail. none of the other input pins do this.

i looked at the original design with the DIP DAC0800 - all the pins settle around 0. So then im thinking what the hell is going on - i changed the SOP DAC for a fresh one - same thing. And again - same thing. I put leads on the SOP package and put them in the DIP socket - same thing. So eventually after I just couldn't think of anything else i broke out the legs of the DIP package and put them on to the SOP pads - no overheating!!

All my SOP DACs are overheating when I connect input 3! What the hell is going on? The datasheet lists no difference between the packages. Could this be a bad batch of chips? I've never had such a thing before! It's so bizarre, please somebody save me from pulling all my remaining hair out

***i actually mean SOIC, rather than SOP.... in case anyone is worried or it makes a difference***
 
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hp1729

Joined Nov 23, 2015
2,304
Im currently transferring an existing design from through hole to surface mount. i got some boards back and made one up, and found the DAC (DAC0800LCM) was overheating. i looked over and over a the circuit and could see no mistake. The original works fine, this one is the layout. I removed the chip out and looked at what was on all the pins - they all looked fine. i measured the resistances between all the pins and ground / power rails blah blah. I eventually put the DAC in and bent all the input pins out so they didn't connect, but left all the rest in - hey presto! No overheating.

I went through one by one and found the culprit - pin 7, input 3. I couldn't see anything untoward about this pin - no shorts on the soldering, no defects on the boards. I removed all connections so it was only connecting to the shift register which drives it - still overheating. This shift register drives all the input pins, so probably not an issue there... I disconnected the pin entirely and measured it to find something odd - it settles at the negative rail. none of the other input pins do this.

i looked at the original design with the DIP DAC0800 - all the pins settle around 0. So then im thinking what the hell is going on - i changed the SOP DAC for a fresh one - same thing. And again - same thing. I put leads on the SOP package and put them in the DIP socket - same thing. So eventually after I just couldn't think of anything else i broke out the legs of the DIP package and put them on to the SOP pads - no overheating!!

All my SOP DACs are overheating when I connect input 3! What the hell is going on? The datasheet lists no difference between the packages. Could this be a bad batch of chips? I've never had such a thing before! It's so bizarre, please somebody save me from pulling all my remaining hair out
On the SOP package the pinout is different from the DIP. Pin 7 is -V.
 

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Thread Starter

pgo1

Joined Nov 7, 2012
48
haha


oh

that explains that then. Remember to read *the whole* datasheet, kids

thanks! Sanity restored
 
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AnalogKid

Joined Aug 1, 2013
8,540
The difference between the two packages is that the SOIC pinout pattern is rotated four positions counter-clockwise WRT the DIP pattern. So if you solder 16 little wires to the SOIC part and tack them down to the rotated positions on the board, the circuit should work.

ak
 

hp1729

Joined Nov 23, 2015
2,304
nice tip. I wonder what the purpose of re-arranging the pins between packages is..
Probably the way the die is set into the package. Rotated 45 degrees off square in the DIP but there may not be enough room in the SOP. Just a guess.
 

Papabravo

Joined Feb 24, 2006
14,252
nice tip. I wonder what the purpose of re-arranging the pins between packages is..
It was tradition on DIP parts to put Vcc and GND at opposite corners of the chip. The placement of decoupling caps, with long leads, was problematical for some applications. Surface mount parts often have different pinouts to accommodate more efficient layouts on multi-layer boards.
 

Papabravo

Joined Feb 24, 2006
14,252
that would be me - it's a one man job. I would probably fire myself if I could
I'm sorry for your pain, but at least you have a sense of humor. Maybe get a friend to lend a hand next time. I can't tell you how many times another pair of eyeballs has saved my bacon.
 

Thread Starter

pgo1

Joined Nov 7, 2012
48
ahh it's fine really. I've not lost too much time and I've patched it up now

true about the eyeballs, though. I wonder how long it would have taken me to notice on my own...
 
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