Re:An alternative to solid tantalum capacitors
by dragontamer on Wednesday March 29, 2017 @09:02AM
(#13985704)
> What are some of the places where tantalum capacitors are required and ceramic capacitors just can't get the job done?
Ceramic Capacitors are a class of class of capacitors. We need to break things down further... Your "NP0" ceramics have great overall characteristics, but are very small... 0805 NP0 ceramics top out at 0.01uF (and are quite expensive at such "high" values).
To get higher capacitance in a ceramic capacitor, you switch over to lower-quality ceramics, like X5R or X7S. X7S gets to 100uF or higher in the 0805 form factor, but are both temperature dependent and voltage dependent.
Here is Murata's "Simsurfing" page, which describes the characteristic on a 100uF 0805 X5R Capacitor.
A 100uF X5R ceramic capacitor by only be 15uF by 5V. Its capacitance changes with voltage. Strangely enough, for most purposes (ie: decoupling), that's not an issue. But any precision circuit (ie: OpAmps or timers) will prefer to use a more voltage-stable capacitor.
Someone else mentioned power-supplies and energy storage. Yeah, a X5R ceramic capacitor has much less energy storage because it loses capacitance as it stores energy (and "high quality" NP0 ceramics just don't have much capacitance to begin with... so no point using those for energy storage).
Ceramic Capacitors are a class of class of capacitors. We need to break things down further... Your "NP0" ceramics have great overall characteristics, but are very small... 0805 NP0 ceramics top out at 0.01uF (and are quite expensive at such "high" values).
To get higher capacitance in a ceramic capacitor, you switch over to lower-quality ceramics, like X5R or X7S. X7S gets to 100uF or higher in the 0805 form factor, but are both temperature dependent and voltage dependent.
Yes, Voltage dependent capacitance.
http://i.imgur.com/mnqbVJC.png
Here is Murata's "Simsurfing" page, which describes the characteristic on a 100uF 0805 X5R Capacitor.
A 100uF X5R ceramic capacitor by only be 15uF by 5V. Its capacitance changes with voltage. Strangely enough, for most purposes (ie: decoupling), that's not an issue. But any precision circuit (ie: OpAmps or timers) will prefer to use a more voltage-stable capacitor.
Someone else mentioned power-supplies and energy storage. Yeah, a X5R ceramic capacitor has much less energy storage because it loses capacitance as it stores energy (and "high quality" NP0 ceramics just don't have much capacitance to begin with... so no point using those for energy storage).
More issues, see: http://www.kemet.com/Lists/TechnicalArticles/Attachments/93/...