0
\$\begingroup\$

I'm used to always use 100 nF (0.1 uF) ceramic capacitors as bypassing capacitors for ICs.

However, in the LM35 datasheet I find two different figures:

enter image description here

The circuit above I need, since I probably want a longer cable between my microcontroller and the LM35 sensor, so I would need a 0.01 uF electrolycal capacitor.

enter image description here

This circuit I don't need, but somehow a 0.01 uF ceramic capacitor is used.

enter image description here

I Also need negative temperatures, and here no bypass capacitor is used.

Questions, if I want e.g. 1 m wires between the LM35 and the microcontroller, should I;

  1. Use a capacitor at all (I think I need since figure 13 shows it).
  2. Should it be ceramic or electrolytical, or doesn't it matter?
  3. Should it be 0.01 uF, or 1 uF?

I am also interesting in some reasoning behind these different capacitor types/values.

\$\endgroup\$
1
  • \$\begingroup\$ The 0.01 is device (internal circuitry) bypass; the 1uF part is part of an output filter for externally induced wiring noise. The value sets the effective cutoff. Having used this family in the past, note that they are highly susceptible to ground currents beneath the device. \$\endgroup\$ – Peter Smith Feb 10 '19 at 15:59
3
\$\begingroup\$

so I would need a 0.01 uF electrolycal capacitor.

You will probably have a very hard time to find a 0.01 uF electrolytic capacitor. As 0.01 uF is only 10 nF I'd say that means it will be a ceramic capacitor.

In case 1 and 2 the 0.01 uF capacitor is optional, I would just add that 10 nF cap. Since this is a very low frequency application (nearly DC) it should not hurt to have the capacitor present.

If you're designing a PCB for this: just add (footprints for) the .01 uF cap. You can always later choose not to mount the capacitor.

The 1 uF in figure 13: you should add it, it is not optional. You do not have to use an electrolytic type, it can be ceramic or other non polarized type as well. Do add the 75 ohm resistor though.

\$\endgroup\$
1
  • \$\begingroup\$ Thanks for the answers and explanation... I thought the line and arced line meant a electrolytical capactor. I will do the tests with the capacitors you propose, thanks. \$\endgroup\$ – Michel Keijzers Feb 10 '19 at 20:20

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.