1. Switching Power Supply Component Selection
7.1b Capacitor Selection – Types of Capacitors

2. Capacitor Chemistry: Value and Voltage rating
100uF uF
Electrolytic
Polymer
0.1uF - 100uF
Tantalum
Capacitance
X5R
X5R/X7R
1pF uF
These are the different types of capacitors available, grouped according to voltage and capacitance availability.
COG
Voltage 2V 4V
16V
25V
50V
100V

3. Aluminum Electrolytics: Overview
Least Expensive Capacitors for Bulk Capacitance
Multiple vendors
Small size, surface mountable
How is it made?
Etched foil with liquid Electrolyte
Placed in a can with a seal/vent
Highest ESR
Low Frequency Cap roll off due to higher ESR
Wear Out Mechanism – Limited lifetime
Liquid electrolyte – with a vent
Cap changes over time with Voltage and Temp
ESR changes over time
Mounting
High shock and vibration can cause failure

4. Aluminum Electrolytics: Packaging
Through hole versions, usually in a round can
Large ones have screw terminals or solder lugs
Radial or axial leads
Non SMT may have higher inductance because of long leads
Surface mountable versions, are modified from radial leaded versions
SMT versions usually have the capacitor value visibly printed on can
SMT versions may use letter codes instead of numeric rating
- +

5. Aluminum Electrolytics
Advantages
Disadvantages
Low Cost
Mature technology with low cost materials
Long History
(Industry started in the 1930’s )
Many Manufacturers to choose from.
High capacitance values available.
Only choice for SMPS that need high voltage and high capacitance.
An electrolytic capacitor is a type of capacitor that uses an electrolyte (an ionic conducting liquid) as one of its plates to achieve a larger capacitance per unit volume than other types, but with performance disadvantages. All capacitors conduct alternating current (AC) and block direct current (DC) and can be used, amongst other applications, to couple circuit blocks allowing AC signals to be transferred while blocking DC power, to store energy, and to filter signals according to their frequency. Most electrolytic capacitors are polarized; hence, they can only be operated with a lower voltage on the terminal marked "-" without damaging the capacitor. This generally limits electrolytic capacitors to supply-decoupling and bias-decoupling, since signal coupling usually involves both positive and negative voltages across the capacitor. The large capacitance of electrolytic capacitors makes them particularly suitable for passing or bypassing low-frequency signals and storing large amounts of energy. They are widely used in power supplies and for decoupling unwanted AC components from DC power connections.
Two types of electrolytic capacitor are in common use: aluminum and tantalum. Tantalum capacitors have generally better performance, higher price, and are available only in a more restricted range of parameters. Solid polymer dielectric aluminum electrolytic capacitors have better characteristics than wet-electrolyte types—in particular lower and more stable ESR and longer life—at higher prices and more restricted values.

6. Aluminum Electrolytics
Advantages
Disadvantages
Large Parasitics
High ESR (Effective Series Resistance)
High ESL – (Effective Series Inductance).
Electrolytic capacitors eventually degrade over the life of the product.
The electrolyte eventually dries out.
Long term storage may cause Aluminum oxide barrier layer to de-form.
Capacitance drops
ESR increases.
Higher ESR causes more internal heat causing it to dry out even faster.
This effect is worse at high temperatures.
(Lesson: Don’t use “old stock” aluminum capacitors in your product.)
Needs a ceramic in parallel for switch mode applications.
High ESR and ESL can cause SMPS malfunction.
Have measurable dc leakage current.
Probably not an issue in power circuits;
Leakage current can be a problem in timing circuits.
Supercapacitors provide the highest capacitance of any practically available capacitor, up to thousands of farads, with working voltages of a few volts. Electrolytic capacitors range downwards from tens (exceptionally hundreds) of thousands of microfarads to about 100 nanofarads—smaller sizes are possible but have no advantage over other types. Other types of capacitor are available in sizes typically up to about ten microfarads, but the larger sizes are much larger and more expensive than electrolytics (film capacitors of up to thousands of microfarads are available, but at very high prices). Electrolytic capacitors are available with working voltages up to about 500V, although the highest capacitance values are not available at high voltage. Working temperature is commonly 85°C for standard use and 105° for high-temperature use; higher temperature units are available, but uncommon.

7. Ceramics: Overview Lowest Cost devices How is it made?
Primarily for decoupling and bypass applications
Multiple vendors, sizes
Surface mountable
How is it made?
Alternating layers of electrodes and ceramic dielectric materials
Significant effects for Class 2 Dielectrics i.e. X5R, X7R
Voltage bias effect
Temperature effects
Ageing
2%/decade hour for X7R
5%/decade hour for X5R
Starts decay after soldering
High Q
Frequency selective

8. Ceramic Dielectric: 3 Character Codes
Class 1 (Best Performance)
Class 2 (Higher Capacitance)
Temperature Coefficient Decoder
Typical Values:
NP0,C0G, values up to 100,000pF
Temperature and Capacitance Tolerance Decoder
Typical Values:
X5R,X7R, values up to 150uF
This table outlines the different classes of capacitors.
Class 1 has Better performance
Class 2 has better capacitance values

9. Ceramic Capacitors Low Cost Many Manufacturers to choose from.
Advantages
Disadvantages
Low Cost
Mature technology with low cost materials
Many Manufacturers to choose from.
Reliable and rugged
Extremely tolerant of over voltage surges
Best Choice for local bypassing
Not Polarized
Lowest effective series resistance (Low ESR)
several milliohms
Leads to high RMS current rating
Low effective series inductance (Low ESL)
< 3nH
A ceramic capacitor is a fixed capacitor with the ceramic material acting as the dielectric. It is constructed of two or more alternating layers of ceramic and a metal layer acting as the electrodes. The composition of the ceramic material defines the electrical behavior and therefor the application of the capacitors which are divided into two stability classes:
Class 1 ceramic capacitors with high stability and low losses for resonant circuit application
Class 2 ceramic capacitors with high volumetric efficiency for buffer, by-pass and coupling applications.

10. Ceramic Capacitors Advantages Disadvantages
Capacitance limited to around 150 uF / 6.3V
Large body sizes prone to cracking with PCB flexing. Several small units in parallel may be a better choice.
Have both a voltage and temperature coefficient that reduces capacitance value.
Some large package size units exhibit piezo-electric audible “singing”.
Difficult to control. (Ceramic speaker effect.)
More noticeable with Class 2 dielectrics
Incomplete data sheets!!
ESR, ESL, SRF and Ripple Current rating often missing from data sheets
Contact the manufacturer for ripple current
Capacitance value not printed on SMT device package.
Impossible to visually inspect for value once mounted on the PCB.
Some power supply circuits are not stable with ceramic output capacitors.
Usually LDO’s and parts using COT control
Ceramic capacitors, especially the multilayer version (MLCC), are the most produced and used capacitors in electronic equipment with a produced quantity of approximately 1000 billion pieces per year.

11. Tantalum: Overview (MnO2 based)
High Capacitance per unit Volume Technology
Small package sizes available
Thin devices are available
How is it made?
Tantalum Anode pressed around a tantalum wire
Oxide grown on surface
Cathode formed by dipping and heat conversion MnMnO2
Epoxy encapsulated
Old technology
Requires 50% Voltage derating
PPM failure rates increase exponentially above 50% voltage derating
Can fail explosively
High ESR compared to Polymer types
Fairly low cap roll off vs. frequency
Tantalum Model

12. Solid Tantalum Capacitors: Packaging
Usually rectangular Surface Mount Technology – SMT machine mountable
Capacitance ratings for 1uF to 1000uF + - + -

13. Solid Tantalum Capacitors
Advantages
Disadvantages
Lots of capacitance in a small package.
1uF to 1000uF max
Medium-high effective series resistance (Low ESR)
10 to 500 milliohms
Medium level of RMS current
Low effective series inductance (Low ESL)
< 3nH
Numerous manufacturers
Good datasheet vs. electrolytic
A tantalum capacitor is a type of electrolytic capacitor, a component of electronic circuits. It typically consists of a pellet of tantalum metal as anode, covered by an insulating oxide layer that forms the dielectric, surrounded by conductive material as a cathode. Tantalum capacitors are the main use of the element tantalum.
The tantalum capacitor distinguishes itself from other capacitors in having high capacitance per volume and weight. Tantalum capacitors have lower equivalent series resistance (ESR), lower leakage, and higher operating temperature than other electrolytic capacitors, although other types of capacitors are even better in these regards.

14. Solid Tantalum Capacitors
Advantages
Disadvantages
Limited voltage range 50V rating max
Therefore for circuit voltages less than 25 or 35VDC
Fairly high in cost
Historically Tantalum has had supply shortages
Limited inrush surge current capability
Do not use tantalum for hot pluggable input capacitors!
Tantalum capacitors are considerably more expensive than any other commonly used type of capacitor, so they are used only in applications where the small size or better performance are important.
Don’t Hot plug tantalum!

15. Solid Tantalum Capacitors Application Safety
ALWAYS
Observe voltage polarity
Potential Outcomes
Can fail catastrophically if misapplied
Can fail open or short
DO NOT
Exceed voltage rating
Exceed inrush surge rating
The low leakage and high capacity of tantalum capacitors favor their use in sample and hold circuits to achieve long hold duration, and some long duration timing circuits where precise timing is not critical. They are also often used for power supply rail decoupling in parallel with film or ceramic capacitors which provide low ESR and low reactance at high frequency. Tantalum capacitors can replace aluminum electrolytic capacitors in situations where the external environment or dense component packing results in a sustained hot internal environment and where high reliability is important. Equipment such as medical electronics and space equipment that require high quality and reliability makes use of tantalum capacitors.
An especially common application for low-voltage tantalum capacitors is power supply filtering on computer motherboards and in peripherals, due to their small size and long-term reliability.
When applying tantalum capacitors, the possibility of thermal runaway (see above) or spontaneous short-circuiting must be considered. In many cases, a failed capacitor will only make the circuit stop functioning normally. However, if sufficient power is available, catastrophic thermal runaway may cause a fire or small explosion. A design can prevent this by using external current limiting (e.g. thermal fuse, circuit breaker).

16. Polymer - Overview Highest Capacitance per unit Volume Technology
Small package sizes available
How is it made?
Tantalum Anode pressed around a tantalum wire
Oxide grown on surface
Cathode formed by dipping into Monomer and cured at room temperature
Epoxy encapsulated
Lower ESR vs MnO2 based Tantalums
Higher frequency operation – over a Mhz…still looks like a cap!
Lower power dissipation
Higher ripple current capability
May need less capacitance 16

17. Polymer & Organic Capacitors: Packaging
SMT Block style similar to tantalum.
Round / Radial versions in SMT and through-hole.
Types
Tantalum polymer / Aluminum polymer / Organic semiconductor
OSCON
Kemet Tantalum Polymer
PosCap

18. Polymer & Organic Capacitors
Advantages
Disadvantages
Low ESR
but not as low as equivalent ceramic.
Low ESL
depending on construction method
New technology
Designed for SMPS.
Can be very low profile.
High capacitance per unit volume.
Much better performance than aluminum electrolytic and much smaller in size.
No voltage coefficient.
Viable alternative to solid tantalum.
Polymer capacitors, conductive polymer (PEDT for example) and polymerized organic semiconductor (TCNQ complex salt for example) capacitors with different chemistry, are types of electrolytic capacitor with solid, rather than the more usual liquid, electrolyte, available since Names used for similar technologies are OS-CON (Sanyo trademark), Aluminum Organic Polymer Capacitors (AO-CAPS), Organic Conductive Polymer Aluminum Electrolytic Capacitor (OC-CON), Functional Polymer Capacitors (FPCAP).

19. Polymer & Organic Capacitors
Advantages
Disadvantages
High cost
Voltage surges capability depends on chemistry.
Oscon very intolerant of voltage surges
Tend to be from a single supplier.
May have availability issues.
Tantalum capacitors are considerably more expensive than any other commonly used type of capacitor, so they are used only in applications where the small size or better performance are important.

20. Polymer & Organic Capacitors Failure Mode
Tantalum Polymer
Less prone to catastrophic failure than solid tantalum but will still vent and emit smoke.
Organic (OSCON)
Emits noxious smoke.

21. Quick Comparison CHARTS

22. Capacitor Chemistry: Quick Comparison
This matrix is helpful as a guide towards capacitor selection based on application.
Red indicates a less than ideal value
Orange indicates a slightly lower than average value
Yellow indicates an average value
Light green indicates a slightly less than ideal value
Green indicates an ideal or recommended value
Numerical Rankings from 1 (Best) to 5 (Worst)

23. Capacitor Chemistry: General Parameters
This table is more technical in illustrating the differences between capacitors of various types. Provides a quantified value for reference.

24. Thank you!