Hi, I need a low dropout voltage regulator and I am studying datasheets. On a few products I have found this definition of dropout voltage (i.e. TS5205):
Dropout voltage is defined as the input to output differential at which the output voltage drops 2% below its nominal value measured at 1V differential.
What "measured at 1V differential" refers to? If it is differential between input and output than it is 1V from definition. What else they may mean?
EDIT: just as I posted it I was enlightened. It means: they measure output voltage when there is 1 V differential between input and output. Then they decrease differential until output drops by 2% - and that differential is the dropout voltage ;-).
Dropout voltage is whatever the marketing department says it is! 2% isn't an unreasonable threshold, but
some applications wouldn't tolerate that (ADC reference voltage for instance)
Note that I think of low dropouts as 0.3--0.4V or so, most marketing departments call anything less than 2V as
"low" (ie anything better than a 78XX !)
Also be aware that near the dropout limit all sorts of performance parameters of the regulator will get worse,
like regulation, output impedance, noise, settling time, and of course any input voltage dips will sail through
the regulator (basically its not regulating any more!)
So if you want to operate with Vin-Vout = 1V, go for a device with 0.5V dropout rather than 0.8V dropout if
you can!
That is why I was studying the datasheets closely because I noticed there are marketing tricks (such as very low dropout as long as Vin is more than 2.5V) and got confused with the definition. The linked regulator has (maximum) dropout 250mV@100mA which is better than I need. I want it for powering LEDs - no need for tight regulation.