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PDF AN203 Data sheet ( Hoja de datos )
| Número de pieza | AN203 | |
| Descripción | C8051FXXX PRINTED CIRCUIT BOARD DESIGN NOTES | |
| Fabricantes | Silicon Laboratories | |
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AN203
C8051FXXX PRINTED CIRCUIT BOARD DESIGN NOTES
1. Introduction
The tips and techniques included in this application note
will help to ensure successful printed circuit board
(PCB) design. Problems in design can result in noisy
and distorted analog measurements, error-prone digital
communications, latch-up problems with port pins,
excessive electromagnetic interference (EMI), and other
undesirable system behavior.
The information in this application note applies to all
C805Fxxx/Txxx devices.
1.1. Key Points
This document includes the following:
Power and ground circuit design tips.
Analog and digital signal design recommendations
with special tips for traces that require particular
attention, such as clock, voltage reference, and the
reset signal traces.
Special requirements for designing systems in
electrically noisy environments.
Techniques for optimal design using multilayer
boards.
A design checklist.
1.2. About this Document
The methods presented in this application note should
be taken as suggestions which provide a good starting
point in the design and layout of a PCB. It should be
noted that one design rule does not necessarily fit all
designs. It is highly recommended that prototype PCBs
be manufactured to test designs. For further information
on any of the topics discussed in this application note,
please read the works cited in "References" on page 20.
2. Power and Ground
All embedded system designs have a power supply and
ground circuit loop that is shared by components on the
PCB. The operation of one component can affect the
operation of other components that share the same
power supply and ground circuit [1].
2.1. Power Supply Circuit
The goal of an embedded system’s power supply is to
maintain a voltage within a specified range while supply-
ing sufficient current. While an ideal power supply would
maintain the same voltage for any possible current
draw, real world systems exhibit the following non-ideal
behaviors:
A change in current and its associated noise caused
by one device affects other devices attached to the
same power supply net.
A change in current draw affects the voltage of the
power net.
Improper use of voltage regulator devices can result
in supply voltage instability.
PCB Power
Connection
Voltage
Regulator
Bulk Decoupling and
Bypass Capacitors
Circuit Conductor:
Traces or Power Planes
IC IC
Local Decoupling and
Bypass Capacitors
Figure 1. Typical Components of a PCB Power Supply
Preliminary Rev. 0.2 7/13
Copyright © 2013 by Silicon Laboratories
AN203
Free Datasheet http://www.datasheet4u.net/
1 page  
AN203
Analog (Low-Frequency) Ground Plane
Line Driver
Digital IC
Digital (High-Frequency) Ground Plane
High frequency digital return currents
can cross ground plane separation
due to capacitance between the
planes. Use at least 1/8” separation
to reduce the capacitance coupling
Digital IC
Digital Ground Currents
Mixed-Signal MCU
(over analog plane)
Analog Ground Currents
Analog IC
Power
Supply
Tie Ground Planes in one place,
close to the power supply
Figure 6. Using Split Analog and Digital Ground Planes
If possible, the mixed-signal MCU should be placed
entirely in the analog ground plane. The MCU may also
reside over both planes, with the divide running under
the device, as shown in Figure 7.
Preliminary Rev. 0.2
5
Free Datasheet http://www.datasheet4u.net/
5 Page 
AN203
5. Isolation And Protection
This section discusses techniques that can be used to
isolate a PCB from noisy external systems, including
particularly noisy industrial systems.
5.1. External Noise Sources
Traces routed to sources outside the PCB may experi-
ence electrostatic discharge (ESD), latch-up, and have
a greater opportunity to share signals with systems that
do not have the same ground potential. For a detailed
discussion on latch-up, ESD, and ground loops, please
see "Appendix A—Rise Time-Related Noise" on page
15.
5.2. Prevention Techniques
A PCB can be protected from these noise sources using
several techniques listed below [1] [5].
Galvanic Isolation – Most commonly accomplished
with optical isolation, which prevents ground loops
and other ESD problems.
Filtering – A series resistor or inductor limits the
amount of current that an ESD event can force into
the PCB, while a shunt capacitance gives high-
frequency noise a low-impedance path to ground.
Transorbs or Schottky Diodes – These components
act to gate high current to power or ground to
prevent ESD damage to the device, and they also
aid in preventing a latch-up condition.
+ VDD Most current goes to voltage
Protected
supply or ground circuit
Pin 100
50 ESD Current
Pulse
Diodes Inc.,
Part no.SDMG0340LS,
GND
(BAT54S)
Figure 12. Example ESD/Latchup
Protection Circuit
Diodes can be used when a PCB’s signal trace inter-
faces with an external component with dissimilar power
and ground voltage supply levels. Figure 12 shows a
diode protection circuit. One diode should be connected
from the signal trace to the voltage supply, and another
should be connected from the trace to ground. To
ensure that the majority of current is gated to power-
ground and not through the protected device, an in-
series resistance on the signal trace should be used in
conjunction with the diode.
5.3. Industrial Systems
Noisy or industrial environments should always be elec-
trically isolated from embedded system PCBs. Industrial
systems can potentially present damaging events to a
PCB. By employing the power, ground, and signal isola-
tion and protection methods discussed in the previous
sections, a PCB will be much less susceptible to all the
detrimental effects of a noisy system.
Preliminary Rev. 0.2
11
Free Datasheet http://www.datasheet4u.net/
11 Page | ||
| Páginas | Total 22 Páginas | |
| PDF Descargar | [ Datasheet AN203.PDF ] | |
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