Toshiba TX79 Series User Manual page 27

3.3 Design
Care must be exercised in the design of electronic equipment to achieve the desired reliability. It is
important not only to adhere to specifications concerning absolute maximum ratings and
recommended operating conditions, it is also important to consider the overall environment in
which equipment will be used, including factors such as the ambient temperature, transient noise
and voltage and current surges, as well as mounting conditions which affect device reliability. This
section describes some general precautions which you should observe when designing circuits and
when mounting devices on printed circuit boards.
For more detailed information about each product family, refer to the relevant individual technical
datasheets available from Toshiba.
3.3.1 Absolute maximum ratings
The absolute maximum ratings are rated values which must not be
exceeded during operation, even for an instant. Although absolute
maximum ratings differ from product to product, they essentially
concern the voltage and current at each pin, the allowable power
dissipation, and the junction and storage temperatures.
If the voltage or current on any pin exceeds the absolute maximum
rating, the device's internal circuitry can become degraded. In the worst
case, heat generated in internal circuitry can fuse wiring or cause the semiconductor chip to break
down.
If storage or operating temperatures exceed rated values, the package seal can deteriorate or the
wires can become disconnected due to the differences between the thermal expansion coefficients
of the materials from which the device is constructed.
3.3.2 Recommended operating conditions
The recommended operating conditions for each device are those necessary to guarantee that the
device will operate as specified in the datasheet.
If greater reliability is required, derate the device's absolute maximum ratings for voltage, current,
power and temperature before using it.
3.3.3 Derating
When incorporating a device into your design, reduce its rated absolute maximum voltage, current,
power dissipation and operating temperature in order to ensure high reliability.
Since derating differs from application to application, refer to the technical datasheets available
for the various devices used in your design.
3.3.4 Unused pins
If unused pins are left open, some devices can exhibit input instability problems, resulting in
malfunctions such as abrupt increase in current flow. Similarly, if the unused output pins on a
device are connected to the power supply pin, the ground pin or to other output pins, the IC may
malfunction or break down.
3 General Safety Precautions and Usage Considerations
Do not use devices under conditions in which their absolute maximum ratings
(e.g. current, voltage, power dissipation or temperature) will be exceeded. A
device may break down or its performance may be degraded, causing it to
catch fire or explode resulting in injury to the user.
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