3 General Safety Precautions and Usage Considerations
3-8
3.3.8 Thermal
design
The failure rate of semiconductor devices is greatly increased as operating temperatures increase.
As shown in Figure 2, the internal thermal stress on a device is the sum of the ambient
temperature and the temperature rise due to power dissipation in the device. Therefore, to
achieve optimum reliability, observe the following precautions concerning thermal design:
(1)
Keep the ambient temperature (Ta) as low as possible.
(2)
If the device’s dynamic power dissipation is relatively large, select the most appropriate
circuit board material, and consider the use of heat sinks or of forced air cooling. Such
measures will help lower the thermal resistance of the package.
(3)
Derate the device’s absolute maximum ratings to minimize thermal stress from power
dissipation.
θ
ja =
θ
jc +
θ
ca
θ
ja = (Tj–Ta) / P
θ
jc = (Tj–Tc) / P
θ
ca = (Tc–Ta) / P
in which
θ
ja = thermal resistance between junction and surrounding air (°C/W)
θ
jc = thermal resistance between junction and package surface, or internal thermal
resistance (°C/W)
θ
ca = thermal resistance between package surface and surrounding 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 dissipation (W)
Tc
θ
ca
Ta
Tj
θ
jc
Figure 2 Thermal resistance of package
3.3.9 Interfacing
When connecting inputs and outputs between devices, make sure input voltage (V
IL
/V
IH
) and
output voltage (V
OL
/V
OH
) levels are matched. Otherwise, the devices may malfunction. When
connecting devices operating at different supply voltages, such as in a dual-power-supply system,
be aware that erroneous power-on and power-off sequences can result in device breakdown. For
details of how to interface particular devices, consult the relevant technical datasheets and
databooks. If you have any questions or doubts about interfacing, contact your nearest Toshiba
office or distributor.
Содержание TMPR7901
Страница 1: ...TX System RISC TX79 Family TMPR7901 Symmetric 2 way superscalar 64 bit CPU ...
Страница 14: ...Handling Precautions ...
Страница 15: ......
Страница 17: ...1 Using Toshiba Semiconductors Safely 1 2 ...
Страница 41: ...4 Precautions and Usage Considerations 4 2 ...
Страница 42: ...TX7901 User s Manual Rev 6 30T November 2001 DOCUMENT NUMBER M 99 00004 07 ...
Страница 43: ......
Страница 259: ...Chapter 13 Removed TX7901 User s Manual Rev 6 30T Nov 2001 13 1 13 Removed ...
Страница 260: ...Chapter 13 Removed TX7901 User s Manual Rev 6 30T Nov 2001 13 2 ...