TECHNICAL INFORMATION BESTCAP®: A NEW GENERATION OF PULSE DOUBLE LAYER CAPACITORS by Bharat Rawal and Lee Shinaberger Advanced Products and Technology Center AVX Corporation Myrtle Beach, SC 29577 Abstract: BestCap®, a new generation of Double Layer Capacitors (DLCs) have been developed to deliver low ESR, high power pulses, or provide back-up power in some applications. These capacitors have values of 10 to 560 mF, voltage ratings of 3.5 to 12 volts and ESR values of 20 to 500 mW. This paper describes the electrical properties of the BestCap ® and it’s endurance under different environmental conditions. Specific applications are shown for illustrative purposes. BESTCAP®: A NEW GENERATION OF PULSE DOUBLE LAYER CAPACITORS by Bharat Rawal and Lee Shinaberger Advanced Products and Technology Center AVX Corporation Myrtle Beach, SC 29577 Introduction: Low ESR BestCap® Devices: Double Layer Capacitors (DLCs), also known as electrochemical or supercapacitors, have been produced in the last twenty-five years as an excellent compromise between batteries and electronic or dielectric capacitors such as ceramic, tantalum or film capacitors. In general, these DLCs have high Equivalent Series Resistance (ESR) and high loss of capacitance when used in pulse power applications. BestCap® capacitors, a new generation of low ESR DLCs, have successfully addressed these two limitations (high ESR and loss of capacitance in the kHz frequency range) by utilizing proton conducting polymer separators, nano-particle carbon electrodes, unique current collectors and other design features. In this paper parameters of these BestCap® devices will be presented, results of reliability testing will be shown and a few applications will be outlined. BestCap® parts are available as prismatic, low profile devices, typically with thickness between 1.6 to 7.5 mm, and the size (length x width) as small as 20 x 15 mm and as large as 48 x 30 mm. Table 1 below shows the three sizes of BestCap® product now available: Table 1 BestCap® Parts come in three sizes: 20 x 15 mm 28 x 17 mm 48 x 30 mm Range of Key parameters of BestCap®: These non-polar, environmentally friendly DLCs are built with a variety of voltage ratings from 3.3 to 12 volts. Figures 1 (a-d) show the range of the four parameters, capacitance, ESR, leakage current and thickness, available in these three sizes: Capacitance Range ESR Range 20x15 20x15 28x17 28x17 48x30 48x30 0.000 0.100 0.200 0.300 0.400 0.500 0.600 0.000 0.100 0.200 Capacitance (F) 0.400 0.500 Thickness Range Leakage Current Range 20x15 20x15 28x17 28x17 48x30 48x30 0.0 0.300 ESR ( Ω ) 5.0 10.0 15.0 20.0 25.0 30.0 35.0 0.0 40.0 Figure 1 (a-d) 2.0 4.0 6.0 Thickness (mm) Leakage Current ( µ A) 2 8.0 10.0 Reliability of BestCap® parts is assessed by testing parts for initial characteristics at room temperature and then by testing them under various environmental test conditions. Table 2 lists these tests, including the load and shelf life (with and without DC bias voltage) for up to 1,000 hours at 60, 70 and 75ºC, cycle life and humidity testing, thermal shock, temperature cycling, vibration and surge voltage. Parts are selectively tested for up to 4,000 hours under load life, and for up to 10 million cycles (parts are tested continuously for about 8 months). Table 2 Test Initial Capacitance Measurement Initial DCL Measurement Initial ESR Measurement Load Life Shelf Life Humidity Life Leg pull strength Surge Voltage Temperature Cycling Temperature Characteristics Thermal Shock Vibration Test Method Discharge cells with a constant current after a full charge noting voltage and time. C = I * dt/dv Apply rated voltage. Note current after exactly 3 hours. Parameter Capacitance (Cap) Leakage Current (DCL) Limits +80% / -20% of rated Cap Within Limit Measurement frequency @ 1kHz; Measurement voltage @ 10 mV Equivalent Series Resistance (ESR) DCL Cap ESR DCL Cap ESR DCL Cap ESR Yield Force (A and L leads only) +20% / -50% of typical value < 2.0x rated max. > 0.7x rated < 3.0x rated < 1.5x rated max. > 0.7x rated < 2.0x rated < 2.0x rated max. > 0.7x rated < 1.5x rated Not less than 25 pounds shear DCL Cap ESR < 1.5x rated max. > 0.7x rated < 1.5x rated DCL Cap < 1.5x rated max. > 0.7x rated ESR < 1.5x rated DCL 70°C < 10x rated Cap Not less than –30% ESR -20°C -10°C 60°C Within +400% Within +300% Within +30% DCL Cap < 2.0x rated max. > 0.7x rated ESR < 2.0x rated max. DCL Cap ESR < 2.0x rated max. > 0.7x rated < 2.0x rated max. Apply rated voltage at 75ºC (A series BestCap), 70ºC (B series BestCap) or 60ºC (C series BestCap) for 1000 hours. Allow to cool to room temperature and measure Cap, DCL and ESR. Maintain at 75ºC (A series BestCap), 70ºC (B series BestCap) or 60ºC (C series BestCap) for 1000 hours Allow to cool to room temperature and measure Cap, DCL and ESR. Maintain at 40°C / 95% RH for 1000 hours. Allow to cool to room temperature and measure Cap, DCL and ESR. Apply an increasing force in shear mode until leg pulls away Step 1 2 3 Step 1 2 Apply 125% of the rated voltage for 10 seconds Short the cell for 10 minutes Repeat 1 and 2 for 1000 cycles Ramp oven down to –20°C and then hold for 30 min. Ramp oven up to 75ºC (A series BestCap), 70ºC (B series BestCap) or 60ºC (C series BestCap) and then hold for 30 min. 3 Repeat 1 and 2 for 100 cycles Step Temp Time 1 -20°C 4 hours Measure Cap, ESR, DCL 2 -10°C 4 hours Measure Cap, ESR, DCL 3 0°C 4 hours Measure Cap, ESR, DCL 5 25°C 4 hours Measure Cap, ESR, DCL 6 40°C 4 hours Measure Cap, ESR, DCL 7 60°C 4 hours Measure Cap, ESR, DCL 8 70°C (A and B series ONLY) 4 hours Measure Cap, ESR, DCL 9 75°C (A series ONLY) 4 hours Measure Cap, ESR, DCL Step 1 Place cells into an oven at –20°C for 30 minutes 2 Move cells into a 75ºC (A series BestCap), 70ºC (B series BestCap) or 60ºC (C series BestCap) oven for 30 minutes 3 Repeat 1 and 2 for 100 cycles Step 1 Apply a harmonic motion that is deflected 0.03 inches 2 Vary frequency from 10 cycles per second to 55 cycles at a ramp rate 3 Vibrate the cells in the X-Y direction for three hours 4 Vibrate the cells in the Z direction for three hours 5 Measure Cap, ESR and DCL These test procedures involve monitoring capacitance (Farads), leakage current (µA) and ESR (milli-ohms or mΩ). Figures 2 - 10 show examples of typical results of such tests. 3 Figure 2 shows initial electrical results: Capacitance, Leakage and ESR data Leakage Current Capacitance Current in Micro Amps Cap in Farads 0.072 0.062 0.052 0.042 0.032 0 10 20 30 40 5 3 1 50 0 50 100 150 Number of Samples Number of Samples Average = 0.054 Std. Dev. = 0.009 Average = 2.4 Std. Dev. = 1.1 ESR in Ohms Equivalent Series Resistance 0.168 0.154 0.140 0.126 0.112 0.098 0.084 0.070 0 5 10 15 20 Number of Samples Average = 0.121 Std. Dev. = 0.012 In all the data shown above and in subsequent figures, the solid lines in the capacitance and ESR graphs show the upper and lower control limits, and the solid line in the leakage current graph shows the upper control limit. It is also critical that physical characteristics be monitored for these products and typical data are shown below: Figure 3: Physical Characteristics Part Height Part Weight 3.510 2.450 Weight in Grams Height in Millimeters 2.600 2.300 2.150 2.000 3.420 3.330 3.240 3.150 0 20 40 60 80 0 20 Number of Samples 40 60 Number of Samples Std. Dev. = 0.044 Average = 3.34 Std. Dev. = 0.023 Figure 4: Load Life (rated voltage and max. rated temperature applied) Capacitance Leakage Current Cap in Farads 0.070 0.060 0.050 0.040 0.030 0.020 0.010 0.420 8 0.350 ESR in Ohms Current in Mirco Farads 0.080 Equivalent Series Resistance 10 6 4 2 0 500 Time in Hrs. 1,000 0.210 0.140 0.070 0 0.000 0.280 0.000 0 500 Time in Hrs. 4 1,000 0 500 Time in Hrs. 1,000 Figure 5: Shelf Life (max. rated temperature applied) Capacitance 0.060 0.050 0.040 0.030 0.020 0.010 10 0.420 8 0.350 ESR in Ohms Current in Micro Amps 0.070 Cap in Farads Equivalent Series Resistance Leakage Current 0.080 6 4 0.280 0.210 0.140 2 0.070 0 0.000 0 500 0.000 0 1,000 500 1,000 0 Time in Hrs. Time in Hrs. 500 1,000 Time in Hrs. Figure 6: Humidity Life (40ºC temperature and 95% humidity applied) Capacitance 0.420 10 0.060 0.050 0.040 0.030 0.020 0.010 0.350 8 ESR in Ohms Current in Mirco Amps 0.070 Cap in Farads Equivalent Series Resistance Leakage Current 0.080 6 4 0.280 0.210 0.140 2 0.070 0 0.000 0 0 500 1,000 Time in Hrs. 500 0.000 1,000 Time in Hrs. 0 500 1,000 Time in Hrs. Leakage Current Equivalent Series Resistance Figure 7: Surge Voltage (125% rated voltage for 10 seconds) Capacitance Current in Micro Amps Cap in Farads 0.070 0.060 0.050 0.040 0.030 0.020 0.010 10 0.420 8 0.350 ESR in Ohms 0.080 6 4 2 0 0.140 0.000 0 1,000 0.210 0.070 0 0.000 0.280 1,000 0 1,000 Number of Cycles Number of Cycles Number of Cycles Figure 8: Temperature Cycling (min to max temp. cycling, slow transition) Capacitance 0.060 0.050 0.040 0.030 0.020 0.010 0.000 0.420 8 0.350 ESR in Ohms Current in Micro Amps Cap in Farads 0.080 0.070 6 4 2 1,000 Number of Cycles 0.280 0.210 0.140 0.070 0.000 0 0 Equivalent Series Resistance Leakage Current 10 0 1,000 Number of Cycles 5 0 1,000 Number of Cycles Figure 9: Thermal Shock (min to max temp. cycling, rapid transition) Leakage Current Capacitance Current in Mirco Amps Cap in Farads 0.070 0.060 0.050 0.040 0.030 0.020 0.010 Equivalent Series Resistance 10 0.420 8 0.350 ESR in Ohms 0.080 6 4 2 0 0.210 0.140 0.070 0 0.000 0.280 0.000 0 1,000 Number of Cycles 1,000 Number of Cycles 0 1,000 Number of Cycles Figure 10: Vibration (10-55Hz, X, Y, and Z axis) Leakage Current Current in Mirco Amps 0 10 9 8 7 6 5 4 3 2 1 0 1,000 0 Number of Cycles 1,000 Number of Cycles Equivalent Series Resistance 0.420 0.350 ESR in Ohms Cap in Farads Capacitance 0.120 0.110 0.100 0.090 0.080 0.070 0.060 0.050 0.040 0.030 0.020 0.010 0.000 0.280 0.210 0.140 0.070 0.000 0 1,000 Number of Cycles 6 Applications: When high power is only required for short periods more sophisticated approaches can be considered. The traditional approach involves using a high power rechargeable battery, charged by a low power primary cell. A far superior solution, however, is the use of a BestCap® Supercapacitor, which is a device specifically designed to deliver high power. In pulse applications, the capacitor discharges to provide a pulse for the circuit. Two factors are critical in determining the voltage drop: ESR and capacitance. The voltage drop caused by the pulse is made up of two terms as shown in Figure 11 below: Traditional Design: Primary Battery Rechargeable Battery Battery Power Equipment Requiring High Current Pulses Design using BestCap® Primary Battery BestCap ® Figure 11: Voltage-Time Relation after Pulse is Initiated The instantaneous voltage drop, VESR is directly proportional to the ESR as shown below, where I is the instantaneous current. VESR = I * ESR Battery Power Equipment Requiring High Current Pulses Figure 12 BestCap® Supercapacitor benefits to the designer are: • Substantially lower voltage drop for pulse durations of up to 100msec. • Substantially lower voltage drop at cold temperatures (-20ºC). • Discharge current limited only by the ESR of the capacitor The time dependent voltage drop VC is inversely proportional to the available capacitance. This is shown in the formula below, where t is the pulse duration and Cf is the available capacitance at the frequency of pulse. VC = I * t / Cf The total voltage drop V is the sum of the instantaneous and time dependant voltage drop as shown below. V = VESR + VC The following analysis compares a primary battery connected in parallel to a Lithium Tionil Chloride, to the same battery connected to a BestCap® Supercapacitor. Various current pulses (amplitude and durations) are applied in each case. Because of the enormous capacitance at high frequencies combined with low ESR, BestCap® outperforms any other solution in pulse applications. BestCap® 5.5V 100mF Table 3 Two application notes will be illustrated in this paper as examples to demonstrate the “pulse power” capability of BestCap®. Pulse 250mA / 1msec 500mA / 1msec 750mA / 1msec 200mA / 100msec at -20ºC 1. Enhancing the Power Capability of Primary Batteries 2. GSM / GPRS PCMCIA modems Votage Drop (mV) Votage Drop (mV) BestCap® Rechargeable Supercapacitor Battery 25 150 50 220 75 150 232 470 BestCap® 3.5V 560mF Pulse 1. ENHANCING THE POWER CAPABILITY OF PRIMARY BATTERIES 250mA / 100msec 500mA / 100msec 750mA / 100msec 1500mA / 1msec 1500mA / 100msec 750mA / 100msec at -20ºC When electronic equipment is powered by a primary (non rechargeable) battery, one of the limitations is the power capability of the battery. In order to increase the available current from the battery, while maintaining a constant voltage drop across the battery terminals, the designer must connect additional cells in parallel leading to increased size and cost of both the battery and finished product. 7 Votage Drop (mV) Votage Drop (mV) BestCap® Rechargeable Supercapacitor Battery 50 190 100 350 152 190 43 220 305 350 172 470 Additional Characteristics Best Cap® Rechargeable Battery Maximum discharge current (single pulse) Not limited 5a Maximum Number of cycles Not limited 40K to 400K (to retain 80% capacity) Table 4: The solution 2. BestCap® FOR GSM/GPRS PCMCIA MODEMS Solution A Chip Tantalum There is an increasing usage of PCMCIA modem cards for wireless LAN and WAN applications. The PCMCIA card is used as an accessory to Laptops and PDA’s, and enables wide area mobile Internet access, including all associated applications like Email and file transfer. With the wide spread use of GSM networks, a PCMCIA GSM modem is a commonly used solution. To achieve higher speed data rates, GSM networks are now being upgraded to support the GPRS standard. Rated Capacitance (milli Farad) Capacitance @ 0.5msec pulse (milli Farad) Working voltage (V) ESR (milli ohm) Size (mm) Voltage Drop* (V) GSM pulse Voltage Drop** (V) GPRS pulse (25% duty cycle) The design challenge: GSM/GPRS transmission requires a current of approximately 2A for the pulse duration. The PCMCIA bus cannot supply this amount of pulsed current. Therefore, there is a need for a relatively large capacitance to bridge the gap. The capacitor supplies the pulse current to the transmitter, and is charged by a low current during the interval between pulses. 1 Solution B BestCap® BestCap® BZ014C353ZSB BZ055B353ZSB 35 35 1 17 17 6.3 4.5 5.5 30 120 110 7.2x6.3x3.8 28x17x2 20x15x4.2 0.9 0.23 0.21 1.75 0.28 0.26 (1) Calculation: *V=V1 + V2 = 1.5A*ESR + (1.5A*0.577msec)/C **V=V1 + V2 = 1.5A*ESR + (1.5A*1.154msec)/C Figure 14 It is assumed that during the pulse, 0.5A is delivered by the battery, and 1.5A is delivered by the capacitor. High capacitance is needed to minimize total voltage drop. A high value capacitance, even with a higher ESR, results in a lower voltage drop in this example. A lower voltage drop reduces the conductive and emitted electromagnetic interference, and increases transmitter output power and efficiency. Summar y: The high capacitance and low ESR of BestCap® supercapacitors provide outstanding performance in pulse applications. Coupled with the wide voltage ratings available, non-toxic materials, and non-polar construction, BestCap® capacitors offer numerous advantages over other capacitor types. Figure 13 NOTICE: Specifications are subject to change without notice. Contact your nearest AVX Sales Office for the latest specifications. All statements, information and data given herein are believed to be accurate and reliable, but are presented without guarantee, warranty, or responsibility of any kind, expressed or implied. Statements or suggestions concerning possible use of our products are made without representation or warranty that any such use is free of patent infringement and are not recommendations to infringe any patent. The user should not assume that all safety measures are indicated or that other measures may not be required. Specifications are typical and may not apply to all applications. © AVX Corporation USA AVX Myrtle Beach, SC Corporate Offices Tel: 843-448-9411 FAX: 843-448-1943 AVX Northwest, WA Tel: 360-699-8746 FAX: 360-699-8751 AVX North Central, IN Tel: 317-848-7153 FAX: 317-844-9314 AVX Mid/Pacific, CA Tel: 510-661-4100 FAX: 510-661-4101 EUROPE AVX Southwest, AZ Tel: 602-678-0384 FAX: 602-678-0385 AVX South Central, TX Tel: 972-669-1223 FAX: 972-669-2090 AVX Southeast, GA Tel: 404-608-8151 FAX: 770-972-0766 AVX Canada AVX Limited, England European Headquarters Tel: ++44 (0) 1252-770000 FAX: ++44 (0) 1252-770001 AVX/ELCO, England Tel: ++44 (0) 1638-675000 FAX: ++44 (0) 1638-675001 AVX S.A., France Tel: ++33 (1) 69-18-46-00 FAX: ++33 (1) 69-28-73-87 AVX GmbH, Germany Tel: ++49 (0) 8131-9004-0 FAX: ++49 (0) 8131-9004-44 AVX srl, Italy Tel: ++390 (0)2 614-571 FAX: ++390 (0)2 614-2576 AVX Czech Republic Tel: ++420 465-358-111 FAX: ++420 465-323-010 Tel: 905-238-3151 FAX: 905-238-0319 ASIA-PACIFIC AVX/Kyocera, Singapore Asia-Pacific Headquarters Tel: (65) 6286-7555 FAX: (65) 6488-9880 AVX/Kyocera, Hong Kong Tel: (852) 2-363-3303 FAX: (852) 2-765-8185 AVX/Kyocera, Korea Tel: (82) 2-785-6504 FAX: (82) 2-784-5411 Elco, Japan Tel: 045-943-2906/7 FAX: 045-943-2910 Kyocera, Japan - AVX Tel: (81) 75-604-3426 FAX: (81) 75-604-3425 Kyocera, Japan - KDP Tel: (81) 75-604-3424 FAX: (81) 75-604-3425 AVX/Kyocera, Taiwan AVX/Kyocera, Shanghai, China Tel: (886) 2-2698-8778 FAX: (886) 2-2698-8777 Tel: 86-21 6886 1000 FAX: 86-21 6886 1010 AVX/Kyocera, Malaysia AVX/Kyocera, Tianjin, China Tel: (60) 4-228-1190 FAX: (60) 4-228-1196 Tel: 86-22 2576 0098 FAX: 86-22 2576 0096 A KYOCERA GROUP COMPANY http://www.avx.com S-BC1M804-N