Electronic – how voltage references work – LM336


In the datasheet for the LM336-5.0 5V reference it uses a 5k resistor fed by 10V. Am I correct in saying that I can give it 12V and it wouldn't matter as long as the current is limited to less than 10mA? It's absolute maximum forward current is 10mA. It's easier for me to feed it 12V because of how I laid out my board.

Best Answer

In normal operation, you would be feeding reverse current through the device, so the Absolute Maximum Rating would be 15mA; the line on the reverse-voltage graph stops at 10mA, but it probably extends pretty straight up to 15mA. Not that one should operate the part there, but one probably shouldn't worry if current gets up to 11mA.

On the other hand, in most cases there's probably not much point in driving the thing with more than 1mA. The graph suggests that the voltage drop will be pretty constant provided there's at least ~0.4mA flowing through it, but the voltage drop falls off very rapidly below that threshold, so one needs to ensure one is operating safely above it. To allow for part variations, 1mA seems like a good safe operating level. The only time I can see usefulness to going above that would be if one has a load whose demand might vary e.g. from 0-8mA. In that case, one might drive (part plus load) with 10mA and figure that the device would have 2-10mA passing through it. Voltage should remain constant provided the load current stays below about 9.5mA.