BD3940HFP 데이터 시트보기 (PDF) - ROHM Semiconductor
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BD3940HFP Datasheet PDF : 9 Pages
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zThermal design
TO252-3
HRP5
TO220FP-3
2.0
1.6
1.2W
1.2
0.8
IC mounted on a ROHM standard board
Board size: 70 mm ×70 mm × 1.6mm
θja = 104.2 (°C /W)
2.0
1.6W
1.6
1.2
0.8
IC mounted on a ROHM standard board
Board size: 70 mm ×70 mm × 1.6mm
θja = 78.1 (°C /W)
0.4
0
0
25
50
75
100 125 150
AMBIENT TEMPERATURE: Ta [℃]
Fig.19
0.4
0
0
25
50
75
100
125 150
AMBIENT TEMPERATURE: Ta [℃]
Fig.20
25
(1)20W
20
(1)無限大放熱板使用時 θja=6.25( /W)
(2)IC 単体時 θja=62.5(℃/W)
15
10
5
(2)2.0W
0
0
25
50
75
100
125 150
AMBIENT TEMPERATURE: Ta [℃]
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:
Power dissipation Pd ≤ Pc
Vo:
Io:
Icc:
The load current Io is obtained to operate the IC within the power dissipation.
Input voltage
Output voltage
Load current
Total supply current
Pd − Vcc × Icc
Io ≤
Vcc − Vo
(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
0.624 −12 × Icc
Io ≤
12 − 5
θja = 104.2°C/W → −9.6 mAW/°C
25°C = 1.2 W → 85°C = 0.624 W
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
zExternal 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.
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