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Transcript
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 100C 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 100C 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