Capacitors in Power Suppliers

TANTALUM
0
5k
R13
100M
SHUT
COMP
13
14
f =
R1
50k
0
0
C1
1n
R8
2k
D1
120NQ045
0
10
GND
8
9
4
5
2
12
11
C_A
CT
E_A
RT
ERRERR+ C_B
E_B
CL+
CL-
R12
100M
1
2π RC
0
+
0
0
C6
NOJC686K006R
R2
1
0
L1
0.9mH
0
C8
0
C9
0
C10
0
TPSV108K004R0035
TPSV108K004R0035
TPSV108K004R0035
+
R7
150
R10
5
+
U1
1
7
6
1
2
L1
0.9mH
Q4
Q2N3703
VREF
OSC
VIN
Q2N3703
+
16
3
R6
68
+
Q3
C3
100n
15
0
C7
NOJC686K006R
+
0
R5
5k
T
1 2
u .dt
T ∫0
u ef =
R16
C11
0
TPSV108K004R0035
0
0
SG1524B
CAPACITORS in
POWER SUPPLIES
“Some 99 percent of the "design" problems associated with linear and switching
regulators can be traced directly to the improper use of capacitors”
Chester Simpson, Member of Technical Staff, Power Supply Design Group, National Semiconductor
issued by technical marketing 1
[email protected]
TANTALUM
0
R16
CONTENT
5k
0
R13
100M
C7
NOJC686K006R
R8
2k
0
D1
120NQ045
R2
1
L1
0.9mH
0
C8
C9
0
SHUT
R1
50k
0
0
1
0
0
0
TPSV108K004R0035
TPSV108K004R0035
TPSV108K004R0035
C1
1n
0
SG1524B
R12
100M
C11
0
TPSV108K004R0035
10
9
8
GND
4
5
COMP
POWER SUPPLIES APPLICATIONS
0
0
0
13
14
C10
+
0
C6
NOJC686K006R
+
12
11
C_A
CT
E_A
RT
ERRERR+ C_B
E_B
CL+
CL-
R10
5
+
7
6
1
2
R7
150
2
VIN
Q4
Q2N3703
U1
VREF
OSC
15
Q2N3703
L1
0.9mH
+
16
3
R6
68
+
Q3
C3
100n
+
CAPACITORS ARE DIFFERENT
R5
5k
SWITCHING REGULATORS
0
LINEAR CONVERTERS
2
TANTALUM
POWER SUPPLIES REQUIREMENTS
ON CAPACITORS
AFFECTING
SMOOTHING CAPABILITY
= V/I RIPPLE
= SIGNAL CLARITY
= FUNCTIONALITY
of end device
•Stable ESR
•Stable Capacitance
•High Frequency Capacitance Retention
•Low Failure Rate
•Wide Voltage Range
•Surge Robust
•Environment (moisture/temperature) Resistant
•Low Cost
3
TANTALUM
CAPACITORS ARE DIFFERENT
Capacitance, ESR with BIAS and temperature
OxiCapTM 10uF/6V
Graph of capacitance stability
Graph of capacitance stability
11
10
10
9
9
9
4
3
2
1
3
6
2
1
DC bias
voltage (V)
Temperature(°C)
Graph of ESR stability
Graph of ESR stability
4
120
7
5
3
4
0
100
Temperature(°C)
120
90
50
30
40
10
20
2
100
7
3
DC bias voltage
(V)
70
6
4
4
1
0
60
5
0
80
120
100
110
80
90
60
70
40
Temperature(°C)
1
5
2
0
50
10
20
30
1
0
Unstable at neg.
temperatures
6
110
2
5
7
80
3
6
8
90
4
7
60
5
8
70
6
40
7
Stable with BIAS
10
20
30
8
Capacitance (uF)
12
11
10
Capacitance (uF)
12
11
7
6
3
2
1
0
5 DC bias voltage
(V)
ESR
Graph of ESR stability
10
10
110
70
20
Temperature(°C)
80
50
60
2
40
3
DC bias voltage
(V)
90
6
4
0
120
7
5
1
100
120
100
40
10
20
Temperature(°C)
80
DC bias
voltage (V)
50
3
60
4
70
5
0,1
110
7
6
2
0
90
120
100
110
70
90
Temperature(°C)
80
60
40
50
30
10
20
0,1
1
Unstable at neg.
temperatures
1
30
0,1
1
High ESR
10
1
ESR (mΩ )#
ESR (Ω )
10
30
Capacitance (uF)
12
50
TANTALUM 10uF/6V
ESR (Ω )
Aluminium
Electrolyte
MLCC X7R, X5R 10uF/6V
Graph of capacitance stability
Capacitance
7
6
5
4
3
2
1
0
DC bias
voltage (V)
4
TANTALUM
CAPACITORS ARE DIFFERENT
Is it important CAP and ESR vs BIAS, Temperature & Frequency ?
OxiCapTM
Aluminium
LTC 1159 with 100uF 4V output capacitor
Tantalum
100uF/4V capacitors
Output dis to rtio n o n DC/DC c o nve rte r
1.0
0.8
DC to DC converter LTC 1159
Input voltage:
15V
Voltage (V)
0.6
0.4
0.2
0.0
-0.2
-0.4
-0.6
-0.8
Output voltage:
Output load:
3,3V DC
3,3ohms
C100/4 OxiCap
-1.0
0
C100/4 Tantalum
10
20
Alumininum 100/6,3
Time
(us )
30
40
50
5
TANTALUM
CAPACITORS ARE DIFFERENT
Is it important CAP and ESR vs BIAS, Temperature & Frequency ?
Tant. 10/10V
Generator with
DC bias voltage 10V
AC 400mV ef. 10kHz
Memory scope
WITH BIAS
Waveforms of AC voltage of 10V source with
10.50
Voltage (V)
MLC 10uF/10V
using different capacitors.
10.00
9.50
Time
Input 10V DC/400mV AC 10kHz
Output from MLC capacitor
Output from Ta capacitor
Volta ge [V]
! 10uF 10V MLCC capacitor at
BIAS
Filte ring e ffe ct of Tantalum A10/10 and ce ramics Y5V 10/16
10V will smooth worse than WITHOUT
0.50
10uF 10V tantalum despite
MLCC ESR is 2 ranges lower !
Input s ignal
0.00
NOT SO OBVIOUS BIAS
Tantalum A10/10
EFFECT looking to spec
-0.50
Ce ramic 10/16
Time
only seems not to be logical
Y5V
6
TANTALUM
CAPACITORS ARE DIFFERENT
Is it important CAP and ESR vs BIAS, Temperature & Frequency ?
25°C
ES R fre que nc y be havio ur @25C
10
Can tantalum polymer capacitor smooth
worse than std (MnO2) capacitor
despite ESR per specification is lower ?
D100/10 55mO Po lyme r
D100/10 100mO S TD TPS
ESR (
)
D100/10 50mO TPS III
1
0.1
0.01
100
1000
10000
ES R fre que nc y be havio ur @85C
100000
10
Fre que nc y (Hz )
D100/10 55mO Po lyme r
)
D100/10 50mO TPS III
1
D100/10 100mO S TD TPS
ESR (
YES it can at applications with
higher operating temperatures,
because ESR drops with
temperature on std tantalum. This
is not the case of the polymer part.
85°C
0.1
0.01
100
1000
10000
100000
Fre que nc y (Hz )
NOT SO OBVIOUS looking to specifications only.
7
TANTALUM
CAPACITORS ARE DIFFERENT
Is it important CAP and ESR vs BIAS, Temperature & Frequency ?
HOW TO MAKE DESIGN EASIER?
AVX simulation programs at www.avxcorp.com
SPICAP (MLCC)
SPITAN II (Ta/OxiCap)
INPUT PARAMETERS
Selected component
-Tantalum capacitor
-Niobium Oxide capacitor
OUTPUT PARAMETERS
-Capacitance, ESR, Impedance
and DF frequency characteristics
-Temperature dependences
8
TANTALUM
CAPACITORS ARE DIFFERENT
Is it important CAP and ESR vs BIAS, Temperature & Frequency ?
Pspice Libraries
0.5
L1
50uH
C1
TAJA226K006R
+
R1
- all major SW libraries on Web
- technical paper guide ready
- high fidelity of model
- frequency & temperature sim
PASSIVE INDUSTRY
LEADING TOOL
R2
5
R3
1u
V1
V2 = 5
PER = 1u
PW = 0.5u
R4
L2
0.5
50uH
C2
22u_10V_Y5V
R6
5
R5
1u
Output v o ltag e le v e l
3
3. 0V
Voltage (V)
2.5
2. 0V
PSpice
simulation
1. 0V
0V
0s
V( i n )
5us
V( o u t )
10us
15us
20us
25us
2
1.5
Real
measurement
1
0.5
0
0
30us
35us
40us
5
10
15
20
25
30
35
40
Time (us )
Ti me
9
TANTALUM
SWITCHING REGULATORS
MLCC
(NPO or COG)
In Q1 ON the Cin is a source
of high energy = must be
High Capacitance
Low Impedance
It can be
Aluminium low ESR
watch for temp. range, reliability, lead-free, size
Tantalum low ESR (TPS series)
watch for surge (correct derating)
OxiCapTM low ESR (NOS series)
for voltages Vin up to 8V peak (10V part)
simple switching regulator
MLCC
watch for transients, capacitance vs BIAS
& cost > 10uF
10
TANTALUM
SWITCHING REGULATORS
REFERENCES
Source: Technical Paper, Linear Technology
stabilization time
22uF ceramic
22uF cer. + 0.5 Ohm
AVX ta TPS 22uF/25V
power up
22uF cer + 30V TVS
47uF leaded Aluminium
Aluminium - good for transient however too high ESR for smoothing
Ceramic – good for high freq. smoothing but risk of transient & oscillation
Tantalum – good compromise, relatively easy for reliable DC/DC design
11
TANTALUM
SWITCHING REGULATORS
REFERENCES
3 x multianode
Ta 470uF 6.3V
“Don’t put high-value ceramic capacitors directly across the fast feedback
inputs without taking precautions to ensure stability. Large ceramic
capacitors can have a high resonance frequency and cause erratic, unstable
operation.”
Source: Maxim 1710 datasheet
12
TANTALUM
SWITCHING REGULATORS
MLCC
Sometimes EMI filter needs to be add to
Vin to minimize RF noise, especially for
high current converters
switching regulator
with L-C filter
MLCC (NPO or COG) is the best choice
for this application (no piezo effect)
13
TANTALUM
SWITCHING REGULATORS
MLCC
Major source of noise is FET,
causing also “ringing”
R-C snubber can be add to
reduce this effect.
disadvantage: efficiency drop
switching regulator
with R-C snubber
High quality MLCC should be used
in this case
14
TANTALUM
SWITCHING REGULATORS
The Cout smoothing the output, so it
should be:
High Capacitance
Low Impedance
It can be:
Tantalum low ESR (TPS series)
watch for ripple current (surge not an issue)
OxiCapTM low ESR (NOS series)
for voltages up to 8V peak (10V product)
Limited usage:
Aluminium electrolytics
switching regulator
high ESR, low ripple current ratings, temp stability
MLCC
ussualy too low capacitance or costly > 10uF
15
TANTALUM
LINEAR REGULATORS
- LDO type (PNP) most favorite
because low drop out voltage
(~0.1V)
- Cout critical for stability
especially ESR range
Linear LDO regulator
Ideal ESR range of
Tantalum (TAJ/TPS series)
OxiCapTM low ESR (NOJ/NOS series)
for voltages up to 8V peak (10V product)
16
TANTALUM
LINEAR REGULATORS
REFERENCES
“For stable operation over the full
operating range, use a 4.7µF (1µF
min) low-cost, high-ESR small size
tantalum capacitor with ESR > 0.5Ω”
Source: M8885 datasheet
4.7uF 10V
Tantalum or
4.7uF 6.3V OxiCapTM
Power Supply converter
for cellular phone Maxim 8885
17
TANTALUM
LINEAR REGULATORS
REFERENCES
Why Tantalums are the Best Choice for Most of the Output Capacitors?
“The stable LDO operation is centered at around 1 Ohm, which matches very
closely with the typical ESR of a Tantalum capacitor of this capacitance value.
The biggest reasons many ICs does not work properly are:
a) Using an aluminum electrolytic output capacitor in a design that operates at cold
temperatures. Aluminum capacitors may have an ESR in the “stable” range at room
temperature, but their ESR increases exponentially as the temperature goes below
about 10 degrees Centigrade. These capacitors must never be used with the IC if
cold temperatures can occur in the application.
b) Using a ceramic output capacitor on an IC not designed for it. The typical 2.2 4.7 uF ceramic capacitor will have an ESR of about 5 milli Ohms. This puts the
resonance frequency somewhere around 6 MHz where it clearly won't help
compensate the loop. Using ceramics on the output of IC which are not designed to
work with them is presently the #1 reason for unstable IC operation.”
Source: National Semiconductor Power IC technical report
18
TANTALUM
LINEAR REGULATORS
REFERENCES
“Another critical characteristic of electrolytics is their
performance over temperature. While the LM2931 is
designed to operate to -40°C, the same is not always
true with all electrolytics”
“As an example, while a high-quality 100µF aluminum
electrolytic covers all general application circuits,
similar stability can be obtained with a tantalum
electrolytic of only 47µF.”
“**C2 must be at least 100 µF to maintain stability.
May be increased without bound to maintain
regulation during transients. Locate as close as
possible to the regulator. The equivalent series
resistance (ESR) of this capacitor is critical.”
Source: LM2931 datasheet
LM2931 is the ideal regulator for standby power systems. Applications include
memory standby circuits, CMOS and other low power processor power supplies
originaly designed for automotive applications.
19
TANTALUM
LINEAR REGULATORS
Latest designs
“Input Capacitor: Any good quality
ceramic or tantalum can be used for
this capacitor”
MLCC
(NPO or COG)
REFERENCES
“OUTPUT CAPACITOR CHARACTERISTICS
Tantalum: Tantalum capacitors are the best choice for use with the
LP2982. In applications which must operate at very low
temperatures, it may be necessary to parallel the output tantalum
capacitor with a ceramic capacitor to prevent the ESR from going
up too high.
Ceramic: Ceramic capacitors are not recommended for use at the
output of the LP2982. This is because the ESR of a ceramic can be
low enough to go below the minimum stable value for the LP2982. If
a ceramic capacitor is used on the output, a 1Ohm resistor should
be placed in series with the capacitor.
Aluminum: Because of large physical size, aluminum electrolytic
are not typically used with the LP2982. They must meet the same
ESR requirements over operating temperature range, which is more
difficult because of their large increase in ESR at cold temperature.
An aluminum electrolytic can exhibit an ESR increase of as much as
50x when going from 20°C to -40°C. Also, some aluminum
electrolytic are not operational below -25°C because the electrolyte
can freeze.”
Source: LP2982 datasheet
Tantalum TPS or OxiCapTM
NOS fits the best
20
TANTALUM
SUMMARY
- capacitor technologies differ in important parameters such as
CAP, ESR and its BIAS, frequency and temperature dependencies
- catalogue data are not sufficient for optimal part design-in
- more capacitor types can be used on input side of switching
regulators, but different parameters to be watched
- output side of switching regulator is not so critical, however
tantalum or OxiCapTM capacitor may fit best
- output side of linear converters is ESR critical, tantalum or
OxiCapTM capacitor fits best for stable operation. MLCC capacitor
can be used on output only in the case that the LDO manufacturer
allows it and then a resistor in series may need to be attached
21