1/ At 125ºC the rated voltage of the capacitors decreases to 66 2/3 of the 85ºC rated voltage.
2/ The peak of the applied ac ripple voltage plus the applied dc voltage must not exceed the dc voltage rating of the capacitors.
2
TWA Series
TWA Wet Electrolytic Tantalum Capacitor
RATINGS & PART NUMBER REFERENCE
AVX Part Number
DSCC
Part
Number
Cap (µF) DC Rated ESR max DC Leakage max (µA)
Impedance
25ºC
Voltage (V) (ohms)
max (Ohms)
+85ºC
+25ºC
at 120Hz
at 85ºC
at 120Hz
& 125ºC -55ºC at 120Hz
Maximum Capacitance
AC Ripple
Change (%)
(mA rms)
85ºC at 40kHz
-55ºC +85ºC +125ºC
Case Size
AVX
DSCC
TWAA127*025C
TWAB567*025C
TWAD128*025C
TWAE188*025C
TWAE228*025C
TWAA107*030C
TWAB477*030C
TWAD108*030C
TWAE158*030C
TWAA686*050C
TWAB227*050C
TWAD477*050C
TWAE687*050C
TWAA476*060C
TWAB157*060C
TWAD397*060C
TWAE567*060C
TWAE108*060C
TWAA336*075C
TWAB117*075C
TWAD337*075C
TWAE477*075C
TWAA156*100C
TWAB686*100C
TWAD157*100C
TWAE227*100C
TWAA106*125C
TWAB476*125C
TWAD107*125C
TWAE157*125C
#@00++
#@00++
#@00++
#@00++
#@00++
#@00++
#@00++
#@00++
#@00++
#@00++
#@00++
#@00++
#@00++
#@00++
#@00++
#@00++
#@00++
#@00++
#@00++
#@00++
#@00++
#@00++
#@00++
#@00++
#@00++
#@00++
#@00++
#@00++
#@00++
#@00++
93026- 29*
93026- 30*
93026- 31*
93026- 32*
93026- 64*
93026- 33*
93026- 34*
93026- 35*
93026- 36*
93026- 37*
93026- 38*
93026- 39*
93026- 40*
93026- 41*
93026- 42*
93026- 43*
93026- 44*
93026- 65*
93026- 45*
93026- 46*
93026- 47*
93026- 48*
93026- 49*
93026- 50*
93026- 51*
93026- 52*
93026- 53*
93026- 54*
93026- 55*
93026- 56*
120
560
1200
1800
2200
100
470
1000
1500
68
220
470
680
47
150
390
560
1000
33
110
330
470
15
68
150
220
10
47
100
150
25
25
25
25
25
30
30
30
30
50
50
50
50
60
60
60
60
60
75
75
75
75
100
100
100
100
125
125
125
125
25 VDC at 85ºC
1.3
1
0.83
2
0.65
5
0.5
6
0.5
4.2
30 VDC at 85ºC
1.3
1
0.85
2
0.7
7
0.6
12
50 VDC at 85ºC
1.5
1
0.9
2
0.75
3
0.7
5
60 VDC at 85ºC
2
1
1.1
2
0.9
3
0.8
5
1
12
75 VDC at 85ºC
2.5
1
1.3
2
1
3
0.9
5
100 VDC at 85ºC
3.5
1
2.1
2
1.6
3
1.2
5
125 VDC at 85ºC
5.5
1
2.3
2
1.8
3
1.6
5
15 VDC at 125ºC
5
10
20
25
27
20 VDC at 125ºC
5
10
25
35
30 VDC at 125ºC
5
10
25
40
40 VDC at 125ºC
5
10
25
40
90
50 VDC at 125ºC
5
10
30
50
65 VDC at 125ºC
5
10
25
50
85 VDC at 125ºC
5
10
25
50
25
12
7
7
2.8
25
15
7
6
35
17.5
10
8
44
20
15
10
6
66
24
12
12
125
37
22
15
175
47
35
20
-42
-65
-70
-75
-65
-38
-65
-70
-72
-25
-50
-50
-58
-25
-40
-60
-58
-80
-25
-35
-45
-55
-18
-30
-35
-40
-15
-25
-35
-35
8
10
12
12
14
8
10
10
10
8
8
8
10
8
8
8
8
10
5
6
6
6
3
4
6
6
3
5
5
6
12
15
18
20
22
12
18
18
20
15
15
15
20
12
15
15
15
20
9
10
10
10
10
12
12
12
10
12
12
12
1250
2100
2600
3100
3200
1200
1800
2500
3000
1050
1800
2100
2750
1050
1650
2100
2750
4000
1050
1650
2100
2750
1050
1650
2100
2750
1050
1650
2100
2750
A
B
D
E
E
A
B
D
E
A
B
D
E
A
B
D
E
E
A
B
D
E
A
B
D
E
A
B
D
E
T1
T2
T3
T4
T4
T1
T2
T3
T4
T1
T2
T3
T4
T1
T2
T3
T4
T4
T1
T2
T3
T4
T1
T2
T3
T4
T1
T2
T3
T4
All technical data relates to an ambient temperature of +25ºC. Capacitance and DF are measured at 120Hz, 0.5RMS with DC bias of 2.2V. DCL is measured at
rated voltage after 5 minutes.
NOTE: AVX reserves the rights to supply higher voltage rating in the same case size, to the same reliability standards.
3
TWA Series
TWA Wet Electrolytic Tantalum Capacitor
Technical Summary and Applications Guidelines
INTRODUCTION
Tantalum capacitors are manufactured from a powder of pure
tantalum metal. The typical particle size is between 2 and 10
µm. Figure below shows typical powders.
The dielectric is then formed over all the Tantalum pentoxide
surface by the electrochemical process of anodization.
To achieve this, the “pellet” is dipped into a very weak
solution of phosphoric acid. The dielectric thickness is
controlled by the voltage applied during the forming process.
Initially the power supply is kept in a constant current mode
until the correct thickness of dielectric has been reached
(that is the voltage reaches the ‘forming voltage’), it then
switches to constant voltage mode and the current decays
to close to zero.
4000µFV
20000µFV
Figure 1. Tantalum powder
The powder is compressed under high pressure around a
Tantalum (known as the Riser Wire) to form a “pellet”. The riser
wire is the anode connection to the capacitor. This is
subsequently vacuum sintered at high temperature (typically
1200 - 1800°C) which produces a mechanically strong pellet
and drives off any impurities within the powder.
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 (see
Figure 2). The larger the surface area the larger the
capacitance. By choosing which powder and sinter
temperature is used to produce each capacitance/voltage
rating the surface area can be controlled.
The following example uses a 220µF 50V capacitor to
illustrate the point.
Figure 2. Sintered Anode
The chemical equations describing the process are as
follows:
Anode:
Cathode:
2 Ta
→
2 Ta
5+
+ 10
e
-
2 Ta
5+
+ 10 OH
-
→
Ta
2
O5 + 5 H
2
O
10 H
2
O – 10 e
→
5H
2
+ 10 OH
The oxide forms on the surface of the Tantalum but it also
grows into the material. For each unit of oxide two thirds
grows out and one third grows into the tantalum surface (see
Figure 3).
Tantalum
C
=
where
o
o r
A
d
and
is the dielectric constant of free space
(8.855 x 10
-12
Farads/m)
r
is the relative dielectric constant
= 27 for Tantalum Pentoxide
d
is the dielectric thickness in meters
C
is the capacitance in Farads
A
is the surface area in meters
Dielectric
Oxide Film
Figure 3. Dielectric layer
Rearranging this equation gives:
A
=
Cd
o r
thus for a 220µF/50V capacitor the surface area is ~2.9
square centimeters, or nearly ten times the size of this page.
4
TWA Series
TWA Wet Electrolytic Tantalum Capacitor
Technical Summary and Applications Guidelines
INTRODUCTION CONTD.
The remaining stages of the process are to contact the dielectric
surface with an electrolyte (which forms the negative contact)
and then establish an external electrical contact layer. As the
name implies, wet tantalums use a wet electrolyte system,
typically sulfuric acid. To establish an external negative contact,
this anode is placed into a cylindrical case which holds the
electrolyte solution. The housing is typically made of tantalum
and becomes part of the cathode of the capacitor. To increase
the effective area of the cathode, thereby increasing the
capacitance, additional cathode material is set inside the case
surrounding the anode of the can.
To complete the assembly of the device, an insulated mount is
inserted into the case providing internal support for the anode.
The anode is inserted and the electrolyte solution dispensed,
then a hermetic insulated seal is applied to the top of the case
Figure 4. Wet Tantalum Construction
allowing the positive riser to exit, and a lead attached to the
other end to make the negative lead. Once this assembly is
complete, the top of the case is welded providing a hermetic
seal.
SECTION 1
ELECTRICAL CHARACTERISTICS AND EXPLANATION OF TERMS
1.1 CAPACITANCE
Capacitance is measured at 120Hz and 25°C with 2.0V DC
bias applied. A small reduction in capacitance level (<2%)
may be observed at rated voltage.
Delta Capacitance (%)
Typical Range of Capacitance
Change over Temperature
10
5
0
-5
-10
-15
-20
-75
-50
-25
0
25
50
75
100
125
150
1.1.1 Rated capacitance.
1.1.2 Capacitance tolerance.
This is the permissible variation of the actual value of the
capacitance from the rated value. For additional reading,
please consult the AVX technical publication “Capacitance
Tolerances for Solid Tantalum Capacitors”.
1.1.3 Temperature dependence of capacitance.
The capacitance of a tantalum capacitor varies with
temperature. This variation itself is dependent to a small
extent on the case size and rating as shown in Figure 1.1.3;
capacitance limits for individual ratings at -55ºC, +85ºC and
+125ºC are given in the data sheet.
Temperature (°C)
Figure 1.1.3: Capacitance Change Limits vs. Temperature
1200
Capacitance (µF)
1000
800
600
400
200
0
680µf 50V T4
1000µf 60V T4
220µf 100V T4
470µf 50V T3
1.1.4 Frequency dependence of the capacitance.
Capacitance levels decrease with increasing frequency.
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