The Circuit Designer's Companion - diagramas.diagram...

180 The Circuit Designer’s Companion5.4.3 Reference specificationsLine and load regulationLine regulation is the change in output voltage due to a specified change in inputvoltage, normally quoted in microvolts per volt. Load regulation is a similar change dueto a change in load current, expressed either in per cent for a given current change or asa dynamic resistance in ohms. It should, but doesn’t always, include self-heating effectsdue to dissipation change.Output voltage toleranceThis is the deviation from nominal output voltage. It is quoted at a given temperatureand input voltage or current, and the nominal voltage will differ under other conditions.Generally it is expressed as a percentage figure, but the asymmetry of device yields maypersuade a manufacturer to quote upper and lower bounds and the nominal figure maynot be in the middle of them. In your circuit design, it is best to ignore the nominalvoltage and work everything out for upper and lower limits.Ouput voltage temperature coefficientThis is the output voltage change due to an ambient temperature difference, usuallyfrom 25˚C. Because neither band-gap nor zener references exhibit a straight linevoltage-temperature curve (see Figure 5.26) manufacturers choose different ways toexpress their tempcos, sometimes as an average value across the range in ppm/˚C,sometimes as different values at a series of spot temperatures, and sometimes as aworst-case error band in mV. To evaluate different manufacturers’ references properlyyou need to correct for these differences in specification.1.237Output voltage V1.2361.235-50 0 +50 +100Temperature ˚CFigure 5.26 Typical band-gap reference temperature characteristicsLong-term stabilityUsually expressed in ppm/1000hr or in microvolts change from the nominal voltage,this is a difficult specification to verify and so is often quoted as a typical figure basedon characterisation of a sample. It is rarely specified on the cheaper components. Zenerstend to stabilise after a couple of years, so for ultra-precision applications the practiceof burning in zener references at high temperatures to speed up the settling process issometimes followed.Settling timeThis is the time taken for the output to settle within a specified error band after