Choosing the wrong decoupling capacitors can have a significant impact on your circuit design. Because different capacitor technologies vary under different conditions, you need to understand which is best for you. This presentation looks at considerations for ceramic, aluminum electrolytic, aluminum polymer, and tantalum capacitors. You can download this presentation at: https://ec.kemet.com/knowledge/choosing-a-decoupling-cap

1. Don’t kill your circuit with the wrong
decoupling capacitor
James Lewis
+1 512 961 6091
jameslewis@kemet.com
Twitter: @baldengineer

2. Outline
• Key attributes to consider for Decoupling
– Capacitance effects from
• Frequency
• Voltage
• Temperature
– Lifetime
• Alternative Technologies Discussed
– Polymer Tantalum
– Aluminum Polymer
– Aluminum Electrolytics
– Supercapacitors
– Ceramics

3. All capacitors utilize the same basic mechanism in their structure
Electrode Plates Dielectric
Basic Capacitor Structure
Different Electrode Dielectric Materials
Give the capacitor different properties

4. What is inside of a Tantalum capacitor?
Tantalum Overview

5. Not All Tantalum Capacitors Burn
• All of the Caps on this board have failed.
– They are measured as shorts
MnO2 MnO2 MnO2 MnO2 MnO2
Poly Poly Poly Poly Poly
Test card with capacitors subjected to 2x Rated Voltage, applied with reverse
polarity and > 20 amperes current capability.
5

6. Dielectric
Anode Cathode
Tantalum
Manganese Dioxide (MnO2) or
Conductive Polymer
Weld
Tantalum (Ta) & Ta2O5 Dielectric
Silver Adhesive
Carbon Ink
Mold Epoxy
Silver Paint
Washer
Tantalum Wire
Solder Coat
Leadframe
Interconnected
Tantalum
Particles
Counter Electrode Penetration into Pores
(Manganese Dioxide (MnO2) or Conductive Polymer)
Carbon Ink
Silver
Paint
Tantalum Construction

7. Tantalum-MnO2 Characteristics
• Significant History
• MIL-PRF Available
• High Temperature (>200C)
• Established Reliability
– (MIL-PRF)
• Cost (sometimes)
• High ESR
– Poor frequency response
– Limits ripple current
– Unstable with temperature
• High voltage derating (50%)
• Ignition when fails

8. KO Caps
Polymer-Ta
Alternatives to MnO2

9. Difference in Self-Healing
MnO2 Polymer
Current through fault
generates enough heat
and oxygen for ignition.
Conductive polymer
consumes oxygen
preventing ignition.
Tantalum Crack
Nickel
Ta Polymer
Polymer
oxidized
Ta2O5
Crack
Nickel
Ta MnO2
Mn2O3
Ta2O5

10. Standard vs. Polymer Tantalum
Capacitance vs. Freq. vs. Temp

11. Standard vs. Polymer Tantalum
ESR vs. Freq. vs. Temp

12. Polymer Tantalum (KO)
Polymer Ta provides the following advantages:
• Benign Failure Mode (No Burning)
• Low ESR
– More Effective Capacitance at higher frequencies
– Can be more cost effective. 100uF vs 47uF
• Less Voltage Derating
– Lower rated voltage may be more cost effective
• Less Board Space
– Less Cap, Lower Voltage: Smaller Size may be possible

13. Low profile solid Aluminum surface mount
Aluminum Polymer (AO)

14. Capacitor Construction
Ta-MnO2
&
KO-Cap AO-Cap

15. Differences in Ta versus Aluminum Structure
No “Wedges” in Al Structure
Tantalum
Smooth and Continuous
Stress Concentrator
Aluminum
• No De-rating for Aluminum Polymers

16. ESR and Impedance vs. Frequency
AO Gen II vs. TA Polymer

17. Capacitance vs. Frequency
AO Gen II vs. TA Polymer

18. Aluminum Polymer (AO)
Aluminum Polymer advantages:
• No Voltage Derating Necessary
– No electrolyte wear-out
– Not sensitive to power-on failures
• Very Low ESR
– ESR approaching ceramics, even at high frequency
• Lower material costs
– No exotic or expensive materials used in construction
• High Capacitance at low voltage
– Relatively high capacitance at 6V or less.

19. “Traditional” aluminum electrolytic can styles
Aluminum Electrolytic (Wet)

20. Capacitor Construction
Anode
Plate
Cathode
Plate

21. 100 uFd ESR vs Freq vs Temp100 uFd ESR vs Freq vs Temp
100
1,000
10,000
100,000
1,000,000
10,000,000
Frequency (Hz)
0.01
0.1
1
10
100
Ohms
KEMET T491D107M006
100
1,000
10,000
100,000
1,000,000
10,000,000
Frequency (Hz)
0.01
0.1
1
10
100
Ohms
SMT AL-Elect. 100 @ 6.3
-55°C
-40°C
0°C
+25°C
+85°C
+105°C
+125°C
+50°C
Aluminum Electrolytic – ESR vs. Freq.

22. 100 uFd Cap vs Freq vs Temp
100
1,000
10,000
100,000
1,000,000
10,000,000
Frequency (Hz)
0.01
0.1
1
10
100
1000
uFd
KEMET T491D107M006
100
1,000
10,000
100,000
1,000,000
10,000,000
Frequency (Hz)
0.01
0.1
1
10
100
1000
uFd
SMT AL-Elect. 100 @ 6.3
-55°C -40°C
0°C
+25°C
+85°C
+105°C
+125°C
+50°C
Aluminum Electrolytic
Capacitance vs Frequency vs Temperature

23. Wet Aluminum vs. Solid Tantalum
Capacitance decay over time
-20
-15
-10
-5
0
0 200 400 600 800 1,000
CapacitanceShift(%)
Time (Hours)
100C Life Test 100µF @ 25VDC
Aluminum
Tantalum

24. Wet Aluminum vs. Solid Tantalum
ESR increase over time
1
10
100
0 200 400 600 800 1,000
ESR(Ohms)
Time (Hours)
100C Life Test 100µF @ 25VDC
Aluminum
Tantalum

25. Aluminum Electrolytic (Wet)
Wet Aluminum Electrolytic advantages:
• High Voltage and High Capacitance
– Surface mount parts >50V possible
• ESR Suitable for bulk decoupling
– Good for low frequency (<10kHz)
• Lower material costs
– No exotic or expensive materials used in construction
• Long life variants available

26. Electrical Double Layer Capacitor
Supercapcitors

27. What is a supercapacitor?
KEMET has always made super capacitors.
Only recently did we introduce
Supercapacitors

28. Traditional and EDLC
Comparison
Tantalum Reference
+
+
+
+
+
+
+
-
-
-
-
-
-
-
MnO2
or CP
Ta2O5
Dielectric
(18-400 nm)
Ta
+
+
+
+
+
+
+
-
-
-
-
-
-
-
C =
Q
V
Solvent
Molecule
(~0.3 to 2 nm)
C
Symmetric
“Supercapacitor”
+
+
+
+
+
+
+
-
-
-
-
-
-
-
C
Separator
C =
e0KA
d
Surface area of carbon
Inner Helmholtz Layer

29. FM, FME,
FML, FMR
3.5V to 6.5V
-40C to +85C
0.022 to 0.22F
Automatic
Insertion
FC, FCS
SMD
Automatic
Mounting
3.5 to 5.5V
-25C to +70C
0.047 to 1F
FT, FG,
FGR,FS, FY,
FR, FE, FA
(Can Case)
5.5 to 12V
-40C to +85C
0.01 to 5.8F
HV
High
Capacitance
2.7V
-25 to +60C
(+70) C
1 to 200F
8 to 32 mm (D)
Supercapacitors

30. Supercapactiors (EDLC)
Supercapacitors provide:
• High Capacitance
– Very high C, but at relatively low voltages
• High Cycle Counts
– 100k, 500k, 1M. (But not Infinite)
Supercapacitors Tradeoffs:
• High ESR
– Good for bulk decoupling (hold-up), but not high frequency ripple
• Low Voltage
– Need more space and to series caps for higher application voltages

31. Multi layer ceramic capacitors
Ceramic

32. Capacitor Constructions
Ceramic
+
-
CT=C1+C2+C3+….Cn

33. Ceramic
How ceramic loses capacitance
C0G (NP0)
Temperature
‘K’Magnitude
X7R
X5R
Z5U
Y5V
‘Room’ Ambient
U2J
Capacitance Change vs. DC Bias
-30%
-25%
-20%
-15%
-10%
-5%
0%
5%
0 10 20 30 40 50
Applied DC Bias (VDC)
CapacitanceChange

34. Ceramic
Ceramic advantages:
• High Voltage, High Capacitance
– Voltage & Temp coefficients must be taken into account
• Ultra low ESR
– Great for high frequency decoupling
• Low material costs
– Very cost effective solution

35. Summary

36. Summary
Choose the decoupling capacitor that is right for your application
• MnO2:
– Cost effective when derated properly
• Polymer-Ta (KO):
– Low ESR, no ignition, high capacitance
• Aluminum Polymer
– Very low ESR, good for low voltage applications
• SMT Aluminum Electrolytic (Wet)
– Good for bulk decoupling or high voltage, but what lifetime
• Supercapacitors
– Good for “Hold-Up” type decoupling, not ripple current
• Ceramic:
– Watch Coefficients! Use Vendor tools to evaluate actual capacitance

37. James Lewis
+1 512 961 6092
jameslewis@kemet.com
Twitter: @baldengineer
Thank You