What's the difference between LM336 and LM385 voltage reference? - Page 1
Forum section: electronics / beginners

author: ElectronSurf
author_rank: Regular Contributor
timestamp: October 29, 2020, 06:13:03 am
content: The LM385 seems like it's a newer device compared to LM336, both have long term stability of 20ppm, LM385 temperature coefficient is 150 ppm/°C but no data for LM336, though in the datasheet it says that we can compensate for temperature drift with two diodes...Which one is more stable with temperature?LM336 datasheet:https://www.ti.com/lit/ds/symlink/lm336-2.5-n.pdfLM385 datasheet:https://www.ti.com/lit/ds/symlink/lm385-adj.pdfBTW how do you attach links to texts?

author: magic
author_rank: Super Contributor
timestamp: October 29, 2020, 07:38:31 am
content: Code:[url=whatever]some textBoth are basic bandgap references without curvature correction. Their thermal drift has a "bow" shape and is plotted further in the datasheet. Looks similar, maybe there is some difference in worst case behavior but they don't seem to give any hard guarantees anyway. Note that one of them shows drift for 1.25V output version.LM385 is lower power and noisier.

author: ElectronSurf
author_rank: Regular Contributor
timestamp: October 29, 2020, 10:14:12 am
content: Quote from: magic on October 29, 2020, 07:38:31 amI'm currently using TL431, I just want to make it a bit more stable if temperature changes (100uV drift == 1mV drift at the output).Do you think that I will see an improvement if I switch to LM336 and add those two diodes like figure 2 in the datasheet?

author: magic
author_rank: Super Contributor
timestamp: October 29, 2020, 04:10:44 pm
content: TL431 works on the same basic principle as these chips and its drift is similar. In general, chips with too high voltage at 25°C are likely to drift upwards with temperature and chips with too low voltage at 25°C are likely to drift downwards. That's why they tell you to adjust the LM336 for exact 2.49V. Same effect can be achieved by selecting a unit which is 2.49V out of the box and then you don't need to worry about coupling the diodes thermally to the chip.And I was wrong, LM336 specification actually does give certain guarantees: see note 4 and the line which refers to note 4.There are better chips than these if you need more.

author: ElectronSurf
author_rank: Regular Contributor
timestamp: October 29, 2020, 04:24:37 pm
content: Quote from: magic on October 29, 2020, 04:10:44 pmAs long as it's better than TL431 it's enough, it's a cheap project, don't want to spend more than that.Thanks for the help.

author: magic
author_rank: Super Contributor
timestamp: October 29, 2020, 07:14:36 pm
content: If it's a one-off and you don't care about manufacturer's guarantees then pick one TL431 from your bag which is closest to 2.495VOr select one which performs best in your application. Observe that for each of those curves, there is a temperature range where it is almost flat and it isn't always 25°C.

author: David Hess
author_rank: Super Contributor
timestamp: October 29, 2020, 09:25:56 pm
content: The best grades of LM336 and LM385 have the same maximum temperature coefficient of up to 30ppm/C. The difference is that the LM385 is an adjustable shunt regulator up to 5 volts, like a low voltage TL431, while the LM336 is a fixed 25 volt reference with a trim range of 10s of millivolts and can be trimmed for zero TC if you want to spend the time temperature cycling it.