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the thickness of the power supply wiring patterns on the printed circuit board. One effective
method, for example, is to devise several shielding options during design, and then select the most
suitable shielding method based on the results of measurements taken after the prototype has
been completed.
3.3.13
Peripheral circuits
In most cases semiconductor devices are used with peripheral circuits and components. The input
and output signal voltages and currents in these circuits must be chosen to match the
semiconductor device's specifications. The following factors must be taken into account.
(1) Inappropriate voltages or currents applied to a device's input pins may cause it to operate
erratically. Some devices contain pull-up or pull-down resistors. When designing your system,
remember to take the effect of this on the voltage and current levels into account.
(2) The output pins on a device have a predetermined external circuit drive capability. If this
drive capability is greater than that required, either incorporate a compensating circuit into
your design or carefully select suitable components for use in external circuits.
3.3.14
Safety standards
Each country has safety standards which must be observed. These safety standards include
requirements for quality assurance systems and design of device insulation. Such requirements
must be fully taken into account to ensure that your design conforms to the applicable safety
standards.
3.3.15
Other precautions
(1) When designing a system, be sure to incorporate fail-safe and other appropriate measures
according to the intended purpose of your system. Also, be sure to debug your system under
actual board-mounted conditions.
(2) If a plastic-package device is placed in a strong electric field, surface leakage may occur due to
the charge-up phenomenon, resulting in device malfunction. In such cases take appropriate
measures to prevent this problem, for example by protecting the package surface with a
conductive shield.
(3) With some microcomputers and MOS memory devices, caution is required when powering on
or resetting the device. To ensure that your design does not violate device specifications,
consult the relevant databook for each constituent device.
(4) Ensure that no conductive material or object (such as a metal pin) can drop onto and short the
leads of a device mounted on a printed circuit board.
3.4
Inspection, Testing and Evaluation
3.4.1
Grounding
3 General Safety Precautions and Usage Considerations
Ground all measuring instruments, jigs, tools and soldering irons to earth.
Electrical leakage may cause a device to break down or may result in electric
shock.
3-10
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