Lostgallifreyan said:
I must practise this. If my crowns will let me. >
Nice thought. I tend to avoid LDO regulators, preferring to reduce the drop
at the rectifier, but I might have to use one some time. Any advice on
which types, or makes, are generally well behaved?
Just got a black eye with the TPS71550. It seems to become unstable with
too much input impedance, resulting in self destruction (they don't have
an overtemp limit) and occasionally taking everything connected into the
grave with it. TI hinted that there might be an issue with source
impedance but insisted on scope plots before they'd investigate further.
It is hard to take scope plots if it blows after a few hundred cycles
and you don't know when. So, I guess we'll ditch that regulator now. I
had sent them my rather simple schematic and they could have thrown that
on the simulator. Nope, not going to happen, they said :-(
Thing is, I can't simulate because they won't release the innards of it.
Ok, I had a 7uA to 2mA load change. Muffled it by easing it on over a
millisecond. They said that might still make it choke up if there was a
high input impedance. My take is that this stuff needs to be mentioned
in datasheets. Either that or good enough SPICE models.
Then there was a National part, LM29xx or something like that with the
same issue. At least they vowed to change the data sheet and mention
that problem.
Then there were a whole lot of others. Forgot the P/Ns and various mfgs
because these weren't my designs. I did the re-design and flung all the
LDOs out the front door immediately.
Anyhow, I won't use LDOs unless there is absolutely no other way.
Usually there is.