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Don't kill your circuit with the wrong decoupling capacitor

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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

Published in: Engineering
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Don't kill your circuit with the wrong decoupling capacitor

  1. 1. Don’t kill your circuit with the wrong decoupling capacitor James Lewis +1 512 961 6091 jameslewis@kemet.com Twitter: @baldengineer
  2. 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. 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. 4. What is inside of a Tantalum capacitor? Tantalum Overview
  5. 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. 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. 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. 8. KO Caps Polymer-Ta Alternatives to MnO2
  9. 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. 10. Standard vs. Polymer Tantalum Capacitance vs. Freq. vs. Temp
  11. 11. Standard vs. Polymer Tantalum ESR vs. Freq. vs. Temp
  12. 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. 13. Low profile solid Aluminum surface mount Aluminum Polymer (AO)
  14. 14. Capacitor Construction Ta-MnO2 & KO-Cap AO-Cap
  15. 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. 16. ESR and Impedance vs. Frequency AO Gen II vs. TA Polymer
  17. 17. Capacitance vs. Frequency AO Gen II vs. TA Polymer
  18. 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. 19. “Traditional” aluminum electrolytic can styles Aluminum Electrolytic (Wet)
  20. 20. Capacitor Construction Anode Plate Cathode Plate
  21. 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. 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. 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. 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. 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. 26. Electrical Double Layer Capacitor Supercapcitors
  27. 27. What is a supercapacitor? KEMET has always made super capacitors. Only recently did we introduce Supercapacitors
  28. 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. 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. 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. 31. Multi layer ceramic capacitors Ceramic
  32. 32. Capacitor Constructions Ceramic + - CT=C1+C2+C3+….Cn
  33. 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. 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. 35. Summary
  36. 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. 37. James Lewis +1 512 961 6092 jameslewis@kemet.com Twitter: @baldengineer Thank You

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