TMPR4937 datasheet(30/552 Pages) TOSHIBA

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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.

θja = θjc + θca

θja = (Tj–Ta) / P

θjc = (Tj–Tc) / P

θca = (Tc–Ta) / P

in which θja = thermal resistance between junction and surrounding air (°C/W)

θjc = thermal resistance between junction and package surface, or internal thermal

resistance (°C/W)

θca = 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)

θca

θjc

Figure 2 Thermal resistance of package

3.3.9

Interfacing

When connecting inputs and outputs between devices, make sure input voltage (VIL/VIH) and output voltage

(VOL/VOH) 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.

TMPR4937 датащи(PDF) 30 Page - Toshiba Semiconductor