Download Alternative Capacitor Platforms to Solid MnO2 Tantalums for

Don’t kill your circuit with the wrong
decoupling capacitor
James Lewis
+1 512 961 6091
[email protected]
Twitter: @baldengineer
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
Basic Capacitor Structure
All capacitors utilize the same basic mechanism in their structure
Electrode Plates
Dielectric
Different Electrode Dielectric Materials
Give the capacitor different properties
Tantalum Overview
What is inside of a Tantalum capacitor?
Not All Tantalum Capacitors Burn
• All of the Caps on this board have failed.
– They are measured as shorts
MnO2
MnO2
Poly
MnO2
Poly
MnO2
Poly
MnO2
Poly
Poly
Test card with capacitors subjected to 2x Rated Voltage, applied with reverse
polarity and > 20 amperes current capability.
5
Tantalum Construction
Tantalum
Interconnected
Tantalum
Particles
Dielectric
Anode
Cathode
Carbon Ink
Silver
Paint
Tantalum (Ta) & Ta2O5 Dielectric Manganese Dioxide (MnO2) or
Conductive Polymer
Mold Epoxy
Carbon Ink
Silver Paint
Counter Electrode Penetration into Pores
Leadframe (Manganese Dioxide (MnO2) or Conductive Polymer)
Silver Adhesive
Solder Coat
Washer
Tantalum Wire Weld
Tantalum-MnO2 Characteristics
• Significant History
• MIL-PRF Available
• High ESR
– Poor frequency response
– Limits ripple current
– Unstable with temperature
• High Temperature (>200C)
• High voltage derating (50%)
• Established Reliability
– (MIL-PRF)
• Cost (sometimes)
• Ignition when fails
Alternatives to MnO2
KO Caps
Polymer-Ta
Difference in Self-Healing
MnO2
Ta2O5
Crack
Polymer
Tantalum
Nickel
Ta
Ta2O5
Mn2O3
Crack
Polymer
oxidized
Nickel
MnO2
Current through fault
generates enough heat
and oxygen for ignition.
Ta
Polymer
Conductive polymer
consumes oxygen
preventing ignition.
Standard vs. Polymer Tantalum
Capacitance vs. Freq. vs. Temp
Standard vs. Polymer Tantalum
ESR vs. Freq. vs. Temp
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
Aluminum Polymer (AO)
Low profile solid Aluminum surface mount
Capacitor Construction
Ta-MnO2
&
KO-Cap
AO-Cap
Differences in Ta versus Aluminum Structure
No “Wedges” in Al Structure
• No De-rating for Aluminum Polymers
Tantalum
Aluminum
Stress Concentrator
Smooth and Continuous
ESR and Impedance vs. Frequency
AO Gen II vs. TA Polymer
Capacitance vs. Frequency
AO Gen II vs. TA Polymer
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.
Aluminum Electrolytic (Wet)
“Traditional” aluminum electrolytic can styles
Capacitor Construction
Anode
Plate
Cathode
Plate
Aluminum Electrolytic – ESR vs. Freq.
100 uFd
uFd ESR
ESR vs Freq vs
100
vs Temp
Temp
SMT AL-Elect. 100 @ 6.3
Ohms
KEMET T491D107M006
Ohms
100
-55°C
100
-40°C
10
10
0°C
+25°C
1
+50°C
+85°C
+105°C
0 .1
0 .0 1
100
+125°C
1 0 ,0 0 0 1 ,0 0 0 ,0 0 0
1 ,0 0 0
1 0 0 ,0 0 0 1 0 ,0 0 0 ,0 0 0
Frequency (Hz)
1
0 .1
0 .0 1
100
1 0 ,0 0 0 1 ,0 0 0 ,0 0 0
1 ,0 0 0
1 0 0 ,0 0 0 1 0 ,0 0 0 ,0 0 0
Frequency (Hz)
Aluminum Electrolytic
Capacitance vs Frequency vs Temperature
100 uFd Cap vs Freq vs Temp
KEMET T491D107M006
SMT AL-Elect. 100 @ 6.3
uFd
uFd
1000
+125°C
+85°C
+105°C +50°C
100
1000
100
+25°C
10
10
1
1
0°C
0.1
0.1
-55°C
0.01
100
1,000
-40°C
10,000
1,000,000
100,000
10,000,000
Frequency (Hz)
0.01
100
1,000
10,000
1,000,000
100,000
10,000,000
Frequency (Hz)
Wet Aluminum vs. Solid Tantalum
Capacitance decay over time
100C Life Test 100µF @ 25VDC
0
Capacitance Shift (%)
Tantalum
-5
-10
Aluminum
-15
-20
0
200
400
600
Time (Hours)
800
1,000
Wet Aluminum vs. Solid Tantalum
ESR increase over time
100C Life Test 100µF @ 25VDC
ESR(Ohms)
100
10
Aluminum
Tantalum
1
0
200
400
600
Time (Hours)
800
1,000
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
Supercapcitors
Electrical Double Layer Capacitor
What is a supercapacitor?
KEMET has always made super capacitors.
Only recently did we introduce
Supercapacitors
Traditional and EDLC
Comparison
Symmetric
“Supercapacitor”
Tantalum Reference
+
+
+
+
+
+
+
Ta
Ta2O5
Dielectric
(18-400 nm)
Q
C=
V
+
+
+
+
+
+
+
-
-
C
MnO2
or CP
+
+
+
+
+
+
+
Solvent
Molecule
(~0.3 to 2 nm)
Separator
C=
C
e0 KA
Surface area of carbon
d
Inner Helmholtz Layer
Supercapacitors
FM, FME,
FML, FMR
FC, FCS
3.5V to 6.5V
-40C to +85C
SMD
Automatic
Mounting
0.022 to 0.22F
Automatic
Insertion
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)
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
Ceramic
Multi layer ceramic capacitors
Capacitor Constructions
Ceramic
+
-
CT=C1+C2+C3+….Cn
Ceramic
How ceramic loses capacitance
Y5V
Capacitance Change vs. DC Bias
Z5U
X5R
X7R
U2J
C0G (NP0)
Capacitance Change
‘K’ Magnitude
5%
0%
-5%
-10%
-15%
-20%
-25%
-30%
0
Temperature
‘Room’ Ambient
10
20
30
Applied DC Bias (VDC)
40
50
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
Summary
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
Thank You
James Lewis
+1 512 961 6092
[email protected]
Twitter: @baldengineer