[sdiy] Negative voltage references

[David G Dixon]

> David,
> 
> " I would say that this is not worth losing sleep over."
> 
> No offence here, but I'd argue on this one. I'd go with the 
> spec. I've been on several projects where the EEs didn't pay 
> attention to things like this and its bitten them. It doesn't 
> look good on their resume when there has been 10000 units 
> shipped and then most the units in manufacturing start 
> failing and the product line is shut down. Turns out it's the 
> original stock of parts has been exhausted and they've 
> ordered the next batch of parts from a different, cheaper 
> vendor. It suprises me that they can get a dozen or so units 
> from China to the states overnight and on the engineers desk 
> when this happens. More than once I've seen this happen.
> 
> Even though the parts that you have work, somewhere someone 
> will use a different brand or batch that will not exceed the 
> specs and they're hosed.
> Also on common parts that are multi-sourced it's not a bad 
> idea to get a number of data sheets and go with the lowest 
> speced one because even though they have the same part number 
> they may have slightly different specs.

I hear you.  However, in this case, I'm not even sure that this is a "spec"
per se.  Nowhere in the datasheet does it say that one must pass at least 1
mA through the device.  the only reference to 1 mA is in the voltage output
specs in the table, where the current is specified between 1 and 100 mA.  It
doesn't say that the device won't work properly if it is not passing at
least 1 mA, and there is one plot where the curve is drawn at 0 mA output.
Why would they bother plotting data at this current if this were not a
viable current for operating the device?

Also, in my case, I only use 79L05 in "non-critical" situations, where I
don't really care all that much how close the reference is, or whether it's
constant with temperature, etc.  In critical situations, I would use a
bandgap reference.