Nemco Electronics Performance Info User Manual
General Performance Information
Introduction
Tantalum capacitors are manufactured from a powder of pure tantalum metal. The powder is compressed under high
pressure around a tantalum wire to form a ‘pellet’. The riser wire is the anode connection to the capacitor. This is subsequently
vacuum sintered at high temperature (typically 1500 - 2000°C). This helps to drive off any impurities within the powder by
migration to the surface. During sintering the powder becomes a sponge like structure with all the particles interconnected in a
huge lattice. This structure is of high mechanical strength and density, but is also highly porous giving a large internal surface area.
The larger the surface area the larger the capacitance. By choosing the powder used to produce each capacitance/voltage
rating, the surface area can be controlled. The next stage is the production of the cathode plate. This is achieved by pyrolysis of
manganese nitrate into manganese dioxide. The ‘pellet’ is dipped into an aqueous solution of nitrate and then baked in an oven
at approximately 250°C to produce a dioxide coat. This process is repeated several times, varying specific densities of nitrate to
build up a thick coat over all internal and external surfaces of the ‘pellet’. The ‘pellet’ is then dipped into graphite and silver to
provide a good connection to the manganese dioxide cathode plate. Electrical contact is established by deposition of carbon onto
the surface of the cathode. The carbon is then coated with a conductive material to facilitate connection to the cathode
termination. Packaging is carried out to meet specifications and customer requirements.
Specifications
Data relates to an ambient temperature of +25° C
z Operating temperature range -55°C to +125°C
PCT, LSR, MCT and TB CGT (Consumer grade) - (linear derating) +40°C to 0.5 x Vr at +85°C and 0.2 x Vr at +125°C.
2/3 x Vr (linear derating) required for operation above +85°C.
z Capacitance Nominal rated capacitance is measured at +25°C, 120 Hz source, free of harmonics with a maximum bias of
2.2V d.c. Capacitance decreases with increasing frequency and increases with increasing temperature.
Typical Component Typical Component
Capacitance vs. Temperature Capacitance vs. Frequency
Capacitance %
% Capacitance Change
Temperature °C Frequency
z Capacitance tolerances E.I.A. standard ±20% and ±10%.
Tolerance is the permissable variation of the actual value of capacitance from the rated value.
z Stability ΔC ≤ 12% over the operating temperature range
C
z Environmental Classification 55/125/56 (IEC 68-2)
General Performance Information
z Working DC voltage range - 4 to 50 WVDC
Rated voltages are the maximum recommended peak DC operating
voltages for continuous use from -55°C to +85°C. Operation above
+85°C requires linear derating to 2/3 rated voltage at +125°C.
To improve operating reliability select higher voltage ratings (30% to 70%
recommended) than the maximum line voltage. This is known as
voltage derating. The effects of voltage derating can be seen by
referring to the section on reliability, failure rate.
z Surge Voltage VDC Surge voltage includes the sum of
peak AC ripple, DC bias and any transients. This is the
highest voltage that may be applied to a capacitor for a short
period of time. The surge voltage may be applied up to ten
times in an hour for periods up to 30 sec. at a time. These
values are not intended to apply to continuous operation.
The surge voltage must not be used as a parameter in the
design of circuits in which, in the normal course of operation,
the capacitor is periodically charged and discharged.
The solid tantalum capacitor has a limited ability to
withstand surges due to the fact that they operate at very
high electrical stress within the oxide layer. It is important to
insure that the voltage across the terminals of the capacitor
does not exceed the surge voltage rating at any time. This
is particularly so in low impedance circuits where the
capacitor is likely to be subjected to the full impact of surges.
Even an extremely short duration spike is likely to cause
damage. In such situations it may be necessary to use a
higher voltage rating such as an extended range value and/or a lower ESR device.
Rated Derated
Working Surge DC Surge
Volts Voltage Volts Voltage
+85°C +85°C +125°C +125°C
4 5.2 2.7 3.2
6.3 8 4 5
10 13 7 8
16 20 10 12
20 26 13 16
25 32 17 20
35 46 23 28
50 65 33 40
% Rated Voltage
Temperature °C
Solid tantalum capacitors have a self healing ability due to the manganese dioxide semicoducting layer used as the negative
plate. In the case of low impedance circuits, the capacitor is likely to be stressed by current surges. Derating the capacitor
voltage by 50% or more increases the reliability of the component. In circuits which undergo rapid charge or discharge a
protective resistor of 1Ω/V is recommended. If this is impossible, a derating factor of up to 70% is recommended. In such
situations a higher voltage may be needed than is available as a single capacitor. A series combination can be used to
increase the working voltage of the equivalent capacitor: For example two 22μF 25V parts in series is equivalent to a 11μF
50V part. 1 ohm per volt series resistance is recommended for dynamic conditions which include current in-rush applications
such as inputs to power supply circuits. In many power supply topologies where the di / dt through the capacitor(s) is limited,
(such as most implementations of buck (current mode), forward converter, and flyback), the requirement for series resistance
is decreased. 0.1 ohm per volt series resistance is recommended for steady state conditions. This level of resistance is used
as a basis for the series resistance variable in a 1% /1000 hours 60% confidence level reference. This is what steady state life
tests are based on.
NOTE: Certain test circuits (i.e. ICT) are likely to subject the capacitors to large voltage and current transients, which will not
be seen in normal use. These conditions should be taken into account when considering the capacitor’s rated voltage for use.
This can be controlled by ensuring a correct test resistance is used.
General Performance Information
z Reverse voltage A small degree of reverse voltage is permissible for short periods. Limiting reverse voltage excursion to
the maximum limits shown will avoid a reduction in the components life expectancy. The maximum allowable reverse
voltage is summarized as follows:
The values quoted are not intended to cover continuous reverse operation.
They are designed to cover exceptional conditions of small levels into reverse polarity.
Non-Polar operation If higher reverse voltages are unavoidable, then two capacitors, each of twice the required
capacitance and of equal tolerance and rated voltage, should be connected in a back-to-back configuration, i.e. both cathodes
joined together.
z DC Leakage Current The DC leakage current is the current that, after a three to five minute charging period, flows through
a capacitor when voltage is applied. It is dependent upon the voltage applied, the time the voltage was applied and th ecomponent temperature. The leakage current increases with increasing temperature. The leakage current decreases when
reduced voltages are applied. The DC leakage current is measured at +25°C with rated voltage applied, through a 1000 ohm
resistor connected in series in the measuring circuit. Reforming of solid tantalum capacitors is unnecessary even after prolonged periods without the application of voltage.
@ 25°C the DCL values are shown in part number tables
@ 85°C the DCL should not exceed 10 times the value
@ 125°C the DCL should not exceed 12 times the value
25°C 10% of rated voltage not exceeding 1.0 volt
85°C 3% of rated voltage not exceeding 0.5 volt
125°C 1% of rated voltage not exceeding 0.1 volt
Temperature Dependance of the Leakage Current
For operation between +85°C and +125°C, the
maximum working voltage must be derated and
can be found from the following formula.
V max = 1 - (T - 85) x V
T is the required operating temperature.
Voltage Dependence of the Leakage Current The leakage current drops
rapidly when reduced voltages are applied. The effect of voltage derating on
leakage current gives a significant increase in reliability for any application.
()
120
R
volts
R25
Leakage Current Ratio I/I
Temperature (°C)
R
Leakage Current Ratio I/IV
Rated Voltage UR %
General Performance Information
z Tan δ(at 120 Hz/25°C) (DF)
Tangent of Loss Angle is a measurement of the energy loss in the capacitor. Terms also used are power factor, loss factor,
quality factor, “Q” (the reciprocal of DF) and DF which is the measurement of Tan δ expressed as a percentage. Tan δ is the
power loss of the capacitor divided by its reactive power at a sinusoidal voltage of a specified frequency. Measurement is
carried out at +25°C and 120Hz with 2.2V DC bias max., with an a.c. voltage free of harmonics. The value of Tan δ
is temperature and frequency dependent. DF increases with increasing frequency. DF loses its importance at higher
frequencies where impedance and ESR are the normal parameters of concern.
Typical Curve Typical Curve
Dissipation Factor (D.F.) vs. Temperature Dissipation Factor (D.F.) vs. Frequency
DF %
Temperature °C Frequency
Tan δ (DF) values are indicated in part number tables. The values shown in the part number tables are the limits met by the
component after soldering onto the substrate.
Tan δ (DF) = R = 2πƒCR Tan δ (DF) = Dissipation factor
X
c
X
z Impedance Impedance is the ratio of voltage to current at a specified frequency. Three factors contribute to the
impedance of a tantalum capacitor; the resistance of the semiconductor layer; the capacitance value and the
inductance of the electrodes and terminations. At high frequencies the inductance of the terminations becomes
a limiting factor. The temperature and frequency behavior of these three factors of impedance determine the
behavior of the impedance. The impedance is measured at +25°C and 100KHz. There is unavoidable
inductance as well as resistance in all capacitors. At some point in frequency, the reactance stops being capacitive and becomes inductive. This frequency is the self resonant point and typically falls between 0.5 - 5MHz
depending on the rating. In solid tantalum capacitors, resonance is damped by the ESR and a smooth transition from capacitive to inductive reactance occurs. Total Impedance of the capacitor can be viewed as:
DF %
R = ESR (ohms)
= Capacitive reactance (ohms)
c
ƒ = Frequency (Hertz)
C = Series capacitance (Farads)
Below resonance - The vector sum of capacitive reactance. X
Above resonance - The vector sum of inductive reactance. ( X
ƒ = frequency, Hertz C = capacitance,farad L = inductance, Henries
z ESR Equivalent Series Resistance (ESR) is the preferred high frequency statement of the unavoidable resistance
appearing in tantalum capacitors. Maximum limits for 100 kHz ESR are listed in the part number tables. NOTE:
Nemco LSR series is specifically designed for low ESR performance. Resistance losses occur in all practical forms
of capacitors. These are made up from several different mechanisms, including resistance in components and
contacts, viscous forces within the dielectric and defects producing bypass current paths. To express the effect of
these losses they are considered as the ESR of the capacitor. The ESR is measured at +25°C and 100KHz. The
ESR is frequency dependent and can be found by using the relationship; ESR = Tan δ
Where ƒ is the frequency in Hertz, and C is the capacitance in farads.
ESR is one of the contributing factors to impedance. At high frequencies (100KHz and above) it becomes the
dominant factor. ESR and impedance become almost identical, impedance being only marginally higher.
= 1 ohm and ESR
c
()
2πƒc
= 2πƒL ) and ESR
L
2πƒC
Loading...