Microchip MCP6V03 Bedienungsanleitung


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2009-2012 Microchip Technology Inc. DS01258B-page 1
AN1258
INTRODUCTION
This application note covers Printed Circuit Board
(PCB) effects encountered in high (DC) precision op
amp circuits. It provides techniques for improving the
performance, giving more flexibility in solving a given
design problem. It demonstrates one important factor
necessary to convert a good schematic into a working
precision design.
This material is for engineers who design slow
precision circuits, including those with op amps. It is
aimed at those engineers with little experience in this
kind of design, but can also help experienced
engineers that are looking for alternate solutions to a
design problem.
The information in this application note can be applied
to all precision (DC) analog designs, with some thought
and diligence. The focus is on common op amp circuits
so that the reader can quickly convert this material into
improvements in their own op amp designs.
Additional material at the end of the application note
includes references to the literature and the schematic
of a PCB used in the design example.
Key Words and Phrases
Op Amp
• Temperature
Thermal Gradient
Thermocouple Junction
Thermoelectric Voltage
IC Sockets
Contact Potential
PCB Surface Contamination
Related Application Notes
The following application notes, together with this one,
form a series about precision op amp design topics.
They cover both theory and practical methods to
improve a design’s performance.
AN1177 on DC Errors [2]
AN1228 on Random Noise [3]
THERMOCOUPLE JUNCTION
BEHAVIOR
While thermocouples are a common temperature
sensor [5], it is not commonly known that every PCB
design includes many unintended thermocouple
junctions that modify the signal voltages. This section
covers the physics behind this effect and gives
practical illustrations.
Seebeck Effect
When two dissimilar conductors (or semiconductors)
are joined together, and their junction is heated, a
voltage results between them (Seebeck or
thermoelectric voltage); this is known as the Seebeck
effect. This voltage is roughly proportional to absolute
temperature. There are many references that discuss
this effect in detail, including the “Temperature
Products” section of reference [8]; see especially
pages Z-13, Z-14 and Z-23 through Z-32.
Figure 1 shows the Seebeck voltage as a function of
temperature for the standard type K thermocouple.
Notice that the response is not strictly linear, but can be
linearized over small temperature ranges (e.g., ±10°C).
FIGURE 1: Type K Thermocouple’s
Response.
Most thermocouple junctions behave in a similar
manner. The following are examples of thermocouple
junctions on a PCB:
Components soldered to a copper pad
Wires mechanically attached to the PCB
• Jumpers
Solder joints
PCB vias
Author: Kumen Blake
Microchip Technology Inc.
10
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o
couple Voltage (mV)
ITS-90
Type K Thermocouple
-10
-5
0
5
10
-300
-200
-100
0
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Therm
o
Thermocouple Temperature (°C)
Op Amp Precision Design: PCB Layout Techniques


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Marke: Microchip
Kategorie: Nicht kategorisiert
Modell: MCP6V03

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