Technical Note

7/11

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2011.03 - Rev.C

© 2011 ROHM Co., Ltd. All rights reserved.

0.0

0.4

0.8

1.2

1.6

2.0

0

25

50

75

100

125

150

Ambient temperature:Ta(℃）

0

5

10

15

20

25

0

25

50

75

100

125

150

Ambient temperature:Ta(℃）

0

1

2

3

4

5

6

7

8

9

10

0

25

50

75

100

125

150

Ambient temperature:Ta(℃）

Mounted on a Rohm standard board

Board size : 70×70×1.6 ㎜

Copper foil area :7×7 ㎜

TO252-5θja=96.2(℃/W)

③

7.3W

②

5.5W

①

2.3W

(1)20.0

(2)2.0

1.30

Board size : 70×70×1.6 ㎜

Board front copper foil area : 10.5×10.5 ㎜

2

①

2-layer board (back surface copper foil area :15×15 ㎜

②

2-layer board (back surface copper foil area :70×70 ㎜

③

4-layer board (back surface copper foil area :70×70 ㎜

When using a maximum heat sick : θj-c=6.25(℃/W)

When using an IC alone : θj-6=62.5(℃/W)

●

Thermal Design

HRP-5

TO220FP-5

TO252-5

Fig.29

Fig.30

Fig.31

When using at temperatures over Ta=25℃, please refer to the heat reducing characteristics shown in Fig.29 through 31. The

IC characteristics are closely related to the temperature at which the IC is used and if the temperature exceeds the maximum

and long-term operating reliability, it is necessary give sufficient consideration to IC heat. In order to protect the IC from

Fig.30 shows the acceptable loss and heat reducing characteristics of the TO220FP package The portion shown by the

diagonal line is the acceptable loss range that can be used with the IC alone. Even when the ambient temperature Ta is a

normal temperature (25℃), the chip (junction) temperature Tj may be quite high so please operate the IC at temperatures

less than the acceptable loss Pd.

The method of calculating the power consumption Pc(W) is as follows.

Pc = (Vcc-Vo) × Io ＋ Vcc × Icca

Acceptable loss Pd≦Pc

Solving this for load current IO in order to operate within the acceptable loss:

Io≦

(Please refer to Figs.8 and 20 for Icca.)

・

Calculation Example

Example 1) When Ta=85℃, Vcc=8.3V, Vo=3.3V, BA33DD0WT

Io≦

With the IC alone : θja=62.5℃/W → -16mW/℃

Io≦200mA (Icca : 2mA)

25℃=2000mW → 85℃=1040mW

Please refer to the above information and keep thermal designs within the scope of acceptable loss for all operating

temperature ranges.

The power consumption Pc of the IC when there is a short circuit (short between Vo and GND) is :

Pc=Vcc×(Icca＋Ishort)

*Ishort : Short circuit current

Pd – Vcc×Icca

Vcc－Vo

1.04－8.3×Icca

5

Vcc：

Vo：

Io：

Vcca：

Input voltage

Output voltage

Load current

Circuit current