hardware developers didactic galactic 0xb: capacitors
TRANSCRIPT
2 Different materials make different capacitors
Electrode Plates Dielectric
Basic Capacitor
C = ε0KA(n−1)d
3
Topic List
• Ceramics– Why they lose capacitance
• Aluminum– Why they don’t last forever
• Tantalum– Why are they are safe to use
• Supercapacitors– Why they are called super
We need a context…
4
Capacitors should be voltage derated 50%
True Or False
It Depends…
5
Ceramics
6
Multilayer Ceramic Capacitor (MLCC)Typical Construction
Ceramic Dielectric
Electrode (Ni for BME, Ag/Pd for PME)
Termination (Cu for BME, Ag for PME)
Finish(Plated Sn)
Barrier Layer (Plated Ni)
+-
Capacitances in parallel are additive
CT=C1+C2+C3+….Cn
C = ε0KA(n−1)d
Max Capacitance is limited by “larger” layers
7
Relative Capacitance vs. TemperatureTemperature Coefficients
C0G (NP0)
Temperature
‘K’
Mag
nitu
de
X7R
X5R
Z5U
Y5V
‘Room’Ambient
U2J
8
Voltage Coefficient (Class II and III)1210 vs 0805, X7R, 10uF, 6.3V
-60%-50%-40%-30%-20%-10%
0%10%
0 1 2 3 4 5 6
Cap
acita
nce
Cha
nge
Applied DC Bias (VDC)
Capacitance Change vs. DC BiasRated 6.3V
How much capacitance do you really get?
1206
0805
9K-SIM: ESR, Z, SPICE Model, VCC, and S-Parameters
ksim.kemet.com
10
X7R Aging Rate1.5% per Decade Hour (Limit)
-14-12-10
-8-6-4-202468
101214
1 10 100 1,000 10,000 100,000
Time Post Heat
Perc
enta
ge N
omin
al
Ref
eren
ce
8,77
7 H
r=1
Yr
87,7
70 H
r =1
0 Y
r
https://ec.kemet.com/aging-calculator-for-ceramics
11
Aluminum Electrolytic
12
Aluminum ElectrolyticForm Factors
Axial/Radial Screw Terminal Snap-In
Single Ended SMD Motor Start
Same construction different form factors
13
CathodePlate
Electrolyte
Aluminum Untreated Surface Area
AnodePlate
C1 C2 If C2 >> C1,then Ct ~ C1
dAC r 0εε=
0ε
( ) 932 =OAlrε
14
dAC r 0εε=
Electrolyte
AnodePlate
Aluminum Acid-Etched Surface Area
C1 C2
C2 must remain >> C1
CathodePlate0ε
15
Anode FoilEtched Surface
16
AluminumAnode
VFormation > VRating > Vapplication
WetElectrolyte
Reformed dielectric regionD
iele
ctric
Dep
letio
n
O-2O-2
Reform
Reforming / Self-Healing Wet Aluminum
Electrolyte“Cathode”
Dielectric
Voltage contributes to operational lifetime
17
Tantalum
18
All Tantalums explode… or do they?
MnO2 MnO2 MnO2 MnO2 MnO2
Poly Poly Poly Poly Poly
2x Rated Voltage, applied with reverse polarity and
>20 amps of current.
18Every capacitor on this board failed as “short”
19
• Stable C (No Temp or Bias Effects), DCL (t)• Reliable (Decreasing FR) • Long Life (Exceeds Expected Life of All Hardware) • Most Volumetrically Efficient (CV/cc, E/cc)
MilitarySpaceMedicalAutomotiveComputersTelecom
Ta
Ta2O5
SEM of a Sintered Ta Anode
Ta
Why use Tantalum?
Ta Oxide Dielectric
20
Polymer Electrolytic:A “new” kind of capacitor
22
Difference in Self-Healing
“Traditional”MnO2
NewPolymer
Current through fault generates enough heat and oxygen for ignition.
Conductive polymer consumes oxygen preventing ignition.
Tantalum Crack
Impurity
Ta Polymer
Polymer oxidized
Ta2O5
Crack
Impurity
Ta MnO2
Mn2O3Ta2O5
If a polymer fails, it fails safely.
23
Tantalum Voltage DeratingDepend on cathode material
• Typical derating guidelines:• Tantalum MnO2: 50%• Tantalum Polymer: 20%(>10V), 10% (≤10V)• Aluminum Polymer: 0%!
35
12
4
0
126%
Ta-Poly KOVR>10VDC
6,310@100% VRated
FR(PPM)
1,700@90% VRated
FR(PPM)
458@80% VRated
FR(PPM)
9@50% VRated
FR(PPM)
0
0
0
0
235%
8
2
1
0
197%68%100 PPM FR
% VRated
Alum-Poly AOTa-Poly KOVR≤10VDC
Ta-MnO2
24
Supercapacitors
25
What Is A “Super” Capacitor?
APowerCap
BestCap
BoostCap
CAP-XX
DLCAP
EneCapTen
EVerCAP
DynaCap
Faradcap
GreenCap
Goldcap
HY-CAP
Super capacitor
SuperCap
AS Capacitor
PowerStor
PseudoCap
Ultracapacitor
Electrostatic Double-Layer Capacitor (EDLC)
26
(Electrical) Double Layers
1. IHP Inner Helmholtz Layer2. OHP Outer Helmholtz Layer3. Diffuse layer4. Solvated ions5. Specifically adsorptive ions6. Solvent molecule
27
Traditional and EDLCComparison
Aluminium Reference
+++++++
-------
AlAl2O3Dielectric
Al
+++++++
-------
C = QV
-------
+++++++
BatteryElectrode
SolventMolecule
(~0.3 to 2 nm)
C
Symmetric“Supercapacitor”
+++++++
-------
C
Separator
+++++++
-------
Asymmetric“Hybrid Capacitor”
C
Separator
C = ε0KAd
Surface area of carbon
Inner Helmholtz Layer
28
Electrolytes
Acetonitrile
– CH3CN– Common for SC– Dielectric constant:
37– Burns to HCN– BP: ~80°C
Propylene Carbonate (PC)– C4H6O3
– Dielectric constant: 64
– Destructive effect on graphite
– BP: ~240°C
Sulfuric Acid
– H2SO4
– Used in lead-acid batteries
– Dielectric constant: ~100
– BP: 337°C
29
Tools
30
Mobile Catalog Apps
Access to over 350 catalogs and 4.8MM data sheets
www.kemet.com/mobileapps
31
ksim.kemet.com
32www.engineeringcenter.com
34
Capacitors should be voltage derated 50%
True Or False
It Depends…
35
Summary
• Ceramic– More capacitance
• Aluminum Electrolytic– Longer operational life
• Tantalum– Power-On Reliability
• Supercapacitors– Operational Life
Why do you voltage de-rate a capacitor?
Slides: www.baldengineer.com/hddg11
36
Thank You!