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Passives
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What Are Passives?
What Do They Do?
What’s Out There To Choose From?
Which One Is Right For Me?
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What Are Passives?
• Passives are components that can
function without a separate power
supply
• The most common are:
- Resistors
- Capacitors
- Inductors
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What Do They Do?
• Basics
– Resistors
– Capacitors
– Inductors
• Common Uses in APA Applications
– Resistors
– Capacitors
– Inductors
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What Do They Do?
• Basics
– Resistors
 Resists Electrical Potential
 Resistivity is constant across the frequency
band
 No energy is stored, only dissipated
– Capacitors
 Stores energy in the electric field
– Inductors
 Store energy in the magnetic field
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What Do They Do?
•Common Uses in APA Applications
– Resistors
 Voltage Dividers
Vcc
R
Vcc
2
R
 Gain Setting
R
R
-
Vcc
 Current Limiting
+
R
Shutdown
 Filtering
R
C
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What Do They Do?
•Common Uses in APA Applications
– Capacitors
 DC Blocking
Vsource
INPUT
C
VDD
 Power Supply
Decoupling
 Filtering
C2
R
C1
C
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What Do They Do?
•Common Uses in APA Applications
– Inductors
L
 Output Filtering
C1
C2
RL
L
 EMI Blocking
C1
 Power Supply
Filtering
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What’s Out There to Choose From?
•
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•
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Mounting Methods
Resistors
Capacitors
Inductors
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What’s Out There to Choose From?
• Mounting Methods
– Thru-Hole
Applies to Resistors, Capacitors, and
Inductors
Component has metal leads that go through
holes on the board
Surface Mount
Applies to Resistors, Capacitors, and
Inductors
Component has no leads. It is soldered
directly down to pads on the board
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What’s Out There to Choose From?
• Resistors
– Thin Film
 Low Distortion
 Excellent TCR (typical between +/-5 and
+/-50 PPM/oC)
 Excellent Tolerance (typical between 0.01
to 0.5%)
 Low Power Ratings are Common
(<1W, often much less)
 Subject to long lead times
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What’s Out There to Choose From?
• Resistors
– Thick Film
 Higher Distortion than Thin Film
 Good TCR (typical between +/-100 and
+/-300, but can go up to +/-1000 PPM/oC)
 Good Tolerance (typical between 1 and 5%)
 Low Power Ratings are Common
(<1W, often much less)
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What’s Out There to Choose From?
• Resistors
– Ceramic
 High Distortion
 TCR is poor (typical > 1000 PPM/oC)
 Tolerance (typical between 5 to 10%)
 Generally thru-hole only
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What’s Out There to Choose From?
• Resistors
– Carbon Film
 Highest Distortion
 TCR can vary greatly (typical between
+/-300 and greater than -1500 PPM/oC)
 Tolerance (typical >5%)
 Generally thru-hole only
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What’s Out There to Choose From?
• Capacitors
– Film (PPS – Polyphenylene Sulfide,
Polypropylene, Polystyrene, Polyester)





Can have low ESR
Values up to 1uF (typically much lower)
TCR < 1% DC/oC
Tolerance from +/-2% to +/-10%
No Piezoelectric Effect
 No Shock Noise
 No audible noise
 High Stability
 0.1395uF/mm3 (ECPU1E105J/K105, 25Vdc)
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What’s Out There to Choose From?
• Capacitors
– MLCC (Multilayer Ceramic Chip)
 Can have low ESR Values up to and
greater than 100uF
 Different types have different ratings
B
 X7R
 X5R
F
 Y5V
TCR= +/10%, Tol = +/-10%, +/-20%
TCR= +/-15%, Tol = +/-10%, +/-20%
TCR= +/-15%, Tol = +/-10%, +/-20%
TCR= +30, -80% Tol = +80, -20%
TCR= +22, -82%, Tol = +80, -20%
 Noisier than Film
 10 to 20dB more distortion than Film
 0.32uF/mm3 (ECJ2FF1E105Z)
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What’s Out There to Choose From?
• Capacitors
– Tantalum
 Can have low ESR
 High capacitance values available
 Can operate over a broad voltage range
 TCR typically +/-10% DC/oC
 Tolerance from +/-5% to +/-20%
 Price and availability fluctuate.
 0.1221uF/mm3 (Kemet T491A105M025AS)
 0.0014uF/mm3 (AVX TAJD107K020R)
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What’s Out There to Choose From?
• Capacitors
– Electrolytic
 Can have low ESR
 Extremely High capacitance values
available
 Can operate over a broad voltage range
 Tolerance typically +/-20%
 Very noisy
 High Distortion
 Large Footprint
 0.0032uF/mm3 (EEUFM1E101)
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What’s Out There to Choose From?
• Capacitors
– ESR
• ESR is Equivalent Series Resistance
• Will cause a voltage drop, even when the
cap looks like a “short”
– ESL
• ESL is Equivalent Series Inductance
• After a certain frequency, the capacitor
begins to “look” like an inductor. The
impedance goes up as the frequency goes
up.
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What’s Out There to Choose From?
• Capacitors
–
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What’s Out There to Choose From?
• Inductors
– Wound Coil
• A length of wire wrapped around a core. Can be an
air core. Must be shielded.
– Torroid Core
• A donut shaped piece of magnetic material around
which a wire is wrapped. High Q, small size,
compact, good at high frequencies, self shielding.
– Ferrite Bead
• Inductive material that maintains a low impedance
throughout the low frequency range, but a high
impedance at high frequencies.
– Common Mode Choke
• Typically made of a Torroid Core, Common Mode
Chokes are used to reduce noise across long lengths
of line.
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Which One Is Right For Me?
• What’s the Application?
• Other Factors
• Guidelines
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Which One Is Right For Me?
• What’s the Application?
– Is component noise an issue?
 No – System could be noisy to begin with
 Yes – Quiet system, such as Hi-Fi
– Is the component in the signal path?
 No – A pullup resistor, a power supply
decoupling cap, inductor in the power
supply path.
 Yes – Gain setting resistors, dc blocking caps,
inductors used for filtering the output.
– Is this a proof of concept prototype or a final
product?
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Which One Is Right For Me?
• Other Factors
– Cost
– Lead time
– Is what I want even manufactured?
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Which One Is Right For Me?
• Guidelines
– Resistors
Signal path of quiet system
– Thin Film
Signal path of noisy system
– Thick Film
Out of signal path
– Thick Film, Ceramic, Carbon Film
Lead Times Unacceptable
– Thick Film
Proof of Concept
– All will work
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Which One Is Right For Me?
• Guidelines
– Capacitors
 Signal path of quiet system
– PPS, Polypropylene, other film
– Low ESR!
 Signal path of noisy system
– MLCC, Tantalum
– Low ESR!
 Power supply decoupling
– MLCC, Electrolytic, Tantalum
– Low ESR!
 Output Filtering
– Film, MLCC
– Low ESR!
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Which One Is Right For Me?
• Guidelines
– Inductors
Proper choice for use (ferrite bead, common
mode choke, etc.)
Correct Value!
Correct Current Rating
Correct Frequency Rating
Low DCR!
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Which One Is Right For Me?
• Guidelines
– Inductors
 Correct Value
 Correct Value is Critical
 Failure to get correct value can cause:
- Shift in cutoff frequency
- Peaking
- High current draw
- Inductor saturation
 Always err on the side of caution! Best to make
the inductor too big rather than too small!
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Which One Is Right For Me?
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Which One Is Right For Me?
Inductor Choices
RL = 8W
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Which One Is Right For Me?
• Guidelines
– Inductors
 Correct Current Rating
 Check ISAT of inductor. Ensure it is greater
than maximum current draw
 Look at curves in inductor datasheet.
Inductance vs. Current curves will indicate how
the inductance drops with current. May be of more
value than just ISAT.
 Correct Frequency Rating
 Check manufacturer curves to determine at what
frequencies the inductance starts to roll off.
 Low DCR!
 The lower the better!
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Which One Is Right For Me?
Inductance vs. Current
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