TMPR4956C Datasheet, PDF (30/286 Pages) Toshiba Semiconductor – 64-Bit TX System RISC TX49 Family

Handling Precautions
3.3.6 Input/Output Protection
Wired-AND configurations in which outputs are connected together directly cannot be used since the outputs
short-circuit with the configurations. Outputs should, of course, never be connected to the power supply voltage
or GND. In addition, products with tri-state outputs can undergo IC deterioration if a shorted output current
continues for a long period of time. Design the circuit so that the tri-state outputs will not be enabled
simultaneously.
3.3.7 Load Capacitance
Certain devices exhibit an increase in delay times and a large charging and discharging current if a large load
capacitance is connected, resulting in noise. In addition, since outputs are shorted for a long period of time,
wiring can become fused. Use the load capacitance recommended for each product.
3.3.8 Thermal Design
The failure rate of semiconductor devices largely increases as the operating temperatures increase. As shown in
Figure 3.2, the thermal stress applied to device internal circuitry is the sum of the ambient temperature and the
temperature rise caused by the power consumption of the device. For thermal design, therefore, refer to the
precautions stated in individual technical datasheets and databooks.
To achieve even higher reliability, take into consideration the following thermal design points:
(1) Conduct studies to ensure that the ambient temperature (Ta) is maintained as low as possible, avoiding the
effects of heat generation from the surrounding area.
(2) If the device’s dynamic power consumption is relatively large, conduct studies regarding use of forced
air-cooling, circuit board composed of low thermal resistance material, and heat sinks. Such measures can
lower the thermal resistance of the package.
(3) Derate the device’s absolute maximum ratings to minimize thermal stress from power consumption.
θja = θjc + θca
θja = (Tj − Ta)/P
θjc = (Tj − Tc)/P
θca = (Tc − Ta)/P
where, θja: Thermal resistance between junction and
ambient air (°C/W)
θjc: Thermal resistance between junction and package
surface, or internal thermal resistance (°C/W)
θca: Thermal resistance between package surface and
ambient air, or external thermal resistance (°C/W)
Tj: Junction temperature or chip temperature (°C)
Tc: Package surface temperature or case temperature (°C)
Ta: Ambient temperature (°C)
P: Power consumption (W)
Ta
θca
Tc
θjc
Tj
Figure 3.2 Thermal Resistance of
Package
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