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***
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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