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BD3941FP Datasheet(PDF) 5 Page - Rohm |
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BD3941FP Datasheet(HTML) 5 Page - Rohm |
5 / 9 page 5/8 Thermal design TO252-3 HRP5 TO220FP-3 Fig.19 Fig.20 Fig.21 Refer to the dissipation reduction illustrated in Figs. 19 to 21 when using the IC in an environment where Ta ≥ 25°C. The characteristics of the IC are greatly influenced by the operating temperature. If the temperature exceeds the maximum junction temperature Tjmax, the elements of the IC may be damaged. It is necessary to give sufficient consideration to the heat of the IC in view of two points, i.e., the protection of the IC from instantaneous damage and the maintenance of the reliability of the IC in long-time operation. In order to protect the IC from thermal destruction, the operating temperature of the IC must not exceed the maximum junction temperature Tjmax. Fig. 19 illustrates the power dissipation/power reduction for the TO252 package. Operate the IC within the power dissipation Pd. The following method is used to calculate the power consumption Pc (W). Pc = (Vcc − Vo) × Io + Vcc × Icc Vcc: Input voltage Power dissipation Pd ≤ Pc Vo: Output voltage Io: Load current Icc: Total supply current The load current Io is obtained to operate the IC within the power dissipation. (Refer to Icc in Fig.12) The maximum load current Iomax for the applied voltage Vcc can be calculated during the thermal design process. Calculation example Example) Vcc = 12 V and Vo = 5.0 V at Ta = 85°C, BD3941FP Io ≤ 89 mA (Icc = 30 µA) Make a thermal calculation in consideration of the above equations so that the whole operating temperature range will be within the power dissipation. The power consumption Pc of the IC, in the event of shorting (i.e., if the Vo and GND pins are shorted), will be obtained from the following equation: Pc = Vcc × (Icc + Ishort) Ishort: Short current External settings for pins and precautions 1) Vcc pin Insert capacitors with a capacitance of 0.33 µF to 1,000 µF between the Vcc and GND pins. The capacitance varies with the application. Be sure to design the capacitance with a sufficient margin. 2) Capacitors for stopping oscillation at output pins Capacitors for stopping oscillation must be placed between each output pin and the GND pin. Use a capacitor within a capacitance range between 1 µF and 1,000 µF. A ceramic capacitor with low ESR values, from 0.001 Ω to 100, can be used. Unstable input voltage and load fluctuations can affect output voltages. Output capacitor capacitance values should be determined for actual application. Io ≤ Pd − Vcc × Icc Vcc − Vo Io ≤ 0.624 −12 × Icc 12 − 5 θja = 104.2°C/W → −9.6 mAW/°C 25°C = 1.2 W → 85°C = 0.624 W 1.2W 1.6W AMBIENT TEMPERATURE: Ta [℃] AMBIENT TEMPERATURE: Ta [℃] (1)20W (2)2.0W AMBIENT TEMPERATURE: Ta [℃] 0.4 0 0.8 1.2 1.6 2.0 0 25 50 75 100 125 150 0.4 0 0.8 1.2 1.6 2.0 0 25 50 75 100 125 150 0 10 15 20 25 5 0 25 50 75 100 125 150 IC mounted on a ROHM standard board Board size: 70 mm ×70 mm × 1.6mm θja = 104.2 (°C /W) IC mounted on a ROHM standard board Board size: 70 mm ×70 mm × 1.6mm θja = 78.1 (°C /W) (1)無限大放熱板使用時 θja=6.25( /W) (2)IC 単体時 θja=62.5(℃/W) |
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