The IC ICL232 needs some capacitors. Should these capacitors be ceramic or any other type?

When does the capacitor type matter?


From the datasheet it is clear that the capacitors have been used for a charge-pump circuit. So it's always preferred to have polarized capacitors in such applications for stability purposes. Since the values are comparatively smaller, you can go for tantalum capacitors.

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    \$\begingroup\$ What do you mean by "stability purpose" ? \$\endgroup\$ – Golaž Mar 10 '15 at 11:48
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    \$\begingroup\$ @Golaž: Aluminum and tantalum electrolytic capacitors — which are the only common polarized types — tend to have higher ESR than non-polarized types, all else being equal. Some types of circuits behave badly when they have to drive a load that has too little impedance. LDO regulators, for example, typically require 1-10 µF of capacitance with an ESR of at least 1 Ω on their output, else they're likely to oscillate. \$\endgroup\$ – Warren Young Mar 10 '15 at 11:58
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    \$\begingroup\$ why tantalum and not aluminum electrolytic? \$\endgroup\$ – user16307 Mar 10 '15 at 22:27
  • \$\begingroup\$ Tantalum capacitors come in a very small packages which makes your board very compact. \$\endgroup\$ – Durgaprasad Mar 11 '15 at 2:05
  • \$\begingroup\$ @user16307: Also, tants don't dry out over time. If you park a typical aluminum electrolytic cap right next to a hot component (like a voltage regulator) it might die in a year or two. Do the same with a tant and it won't care. But, tants are expensive and don't come in very large values. The value needed here is within the range of reasonably-priced tants. \$\endgroup\$ – Warren Young Mar 11 '15 at 18:20

Yes, the type of capacitor can matter. Different types of capacitor have different properties.

Some of the properties that vary between capacitor types:

  • Polarised vs unpolarised
  • Max voltage
  • Equivalent Series Resistance (ESR)
  • Lifetime (electrolytics are particularly bad in this case)
  • Physical size (e.g. a 100,000 uF ceramic capacitor would be HUGE!)
  • Tolerance of capacitance (again, electrolytics are bad here, often being +/- 20%

In your link, the diagram shows polarised capacitors, which suggests that they weren't intended to be ceramic (which are unpolarised).

Two types of polarised capacitors are aluminum and tantalum electrolytics. In your case, I'd use tantalum.

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  • \$\begingroup\$ What about the impact of ambient temperature? \$\endgroup\$ – Paul A. Clayton Mar 10 '15 at 11:27
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    \$\begingroup\$ I would also like to add that X/Y safety ratings are a big difference if you are designing for AC lines (AC/DC converters, for example). Not for IC decoupling use but figured I'd sneak this comment in on a good answer. \$\endgroup\$ – scld Mar 10 '15 at 11:55
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    \$\begingroup\$ What if I use ceramic ones? Why would you prefer tantalum and not aluminum electrolytic? \$\endgroup\$ – user16307 Mar 10 '15 at 22:26
  • \$\begingroup\$ Don't forget about inductance and Q factor. These are very important for high frequency applications (RF/microwave). \$\endgroup\$ – alex.forencich Mar 11 '15 at 5:04
  • \$\begingroup\$ Why not ceramic? I'm not sure if there are any reasons /not/ to use ceramic; I'm not sure I know enough about your particular application to decide. However, since the schematic suggests polarised caps, I'd tend to go along with that. As for tantalum vs electrolytic, about the only advantage that electrolytics have over tantalum (at the lower capacitance end) is cost. As previously mentioned, the tolerance is poor (although I suspect that this probably doesn't matter in your case), but the main reason is lifetime. They degrade over time, and eventually fail. \$\endgroup\$ – David Smith Mar 11 '15 at 9:04

Capacitor type can matter quite a bit. Small, high value, type 2 Ceramic capacitors have two significant disadvantages, one of which applies to use in this application with the ICL232:

  • The capacitance varies substantially with voltage. Under certain circumstances, your 4.7 uF cap may act more like an 0.33 uF cap. Maxim has posted a very nice tutorial on this topic: http://www.maximintegrated.com/en/app-notes/index.mvp/id/5527
  • The ceramic dialectric exhibits the piezoelectric effect. This means that the capacitor may exhibit microphonics undesirable in low-level audio circuits. (This could also cause the capacitors to emit sounds with substantial changes in applied voltage.)

So, for large value bypass caps, or for switched-capacitor power supplies, try to use polarized tantalum (smaller and more stable, but more expensive), electrolytic (cheaper, larger packages, less stable with age), or larger-bodied ceramic (moderate cost, more stable, require more board area).

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The datasheet is not very specific about the capacitors. X7R ceramics should work well. Small, inexpensive, can't put them in backwards. Class 2 ceramics are modulated by voltage so use the highest voltage part you can, 25 volt maybe.

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