BestCap : A New Generation of Pulse Double Layer Capacitors

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.
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