BD3021HFP-M Ver la hoja de datos (PDF) - ROHM Semiconductor
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BD3021HFP-M Datasheet PDF : 15 Pages
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BD3021HFP-M
●Thermal Design
Technical Note
10
Mounted on a Rohm standard board
Board size : 70 ㎜×70 ㎜×1.6 ㎜
θja=78.1(℃/W)
8
6
4
1.60W
2
10
8 ③7.3W
②5.5W
6
Mounted on a Rohm standard board
Board size : 70 ㎜×70 ㎜×1.6 ㎜
(board contains a thermal)
①2-layer board
(back surface copper foil area :15 ㎜×15 ㎜)
②2-layer board
(back surface copper foil area :70 ㎜×70 ㎜)
③4-layer board
(back surface copper foil area :70 ㎜×70 ㎜)
①θja=54.3(℃/W)
②θja=22.7(℃/W)
③θja=17.1(℃/W)
4
①2.3W
2
0
0
25
50
75
100
125
150
AMBIENT TEMPERATURE:Ta[℃]
Fig.14
0
0
25
50
75
100
125
150
AMBIENT TEMPERATURE:Ta[℃]
Fig.15
Refer to Fig.14 and Fig.15 thermal dissipation characteristics for usage above Ta=25℃. The IC’s characteristics are affected
heavily by the temperature, and if is exceeds its max junction temperature (Tjmax), the chip may degrade or destruct.
Thermal design is critical in terms of avoiding Instantaneous destruction and reliability in long term usage. The IC needs to
be operated below its max junction temperature (Tjmax) to avoid thermal destruction. Refer to Fig.14 and Fig.15 for HRP7
package thermal dissipation characteristics. Operate the IC within power dissipation (Pd) when using this IC.
Power consumption Pc(W) calculation will be as below (for Fig.15③)
Pc=(Vcc－VOUT)×Io+Vcc×Icc2
Power dissipation Pd≧Pc
Vcc : Input Voltage
VOUT : Output Voltage
Io : Load Current
Icc2 : Circuit Current
If load current Io is calculated to operate within power dissipation, it will be as below, where you can find the max load current
IoMax for the applied voltage Vcc of the thermal design.
Io ≦
Pd－Vcc×Icc2
Vcc－VOUT
(Refer to Fig2 for Icc2)
Example) at Ta=125℃,Vcc=12V,VOUT=5V
Io ≦
1.46－12×Icc2
12－5
Io ≦ 208mA (Icc2=150µA)
Fig.15③ : θja=17.1℃/W → -58.4mW/℃
25℃=7.3W → 125℃=1.46W
Refer to above and adjust the thermal design so it will be within power dissipation within the entire operation temperature
range. Below is the power consumption Pc calculation when (VOUT-GND short)
Pc=Vcc×(Icc2+Ishort)
Ishort: short current
(Refer to Fig.4 for I short)
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10/14
2010.11 - Rev.A
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