BA78□□Series,BA78M□□Series

Technical Note

10/12

www.rohm.com

2012.03 - Rev.C

© 2012 ROHM Co., Ltd. All rights reserved.

●Thermal design

Refer to the following thermal derating curves (Fig. 25, 26), when using in the status of Ta=25℃ or more.

The characteristic of IC is greatly related to the operating temperature.

When it is used in over maximum junction temperature, the elements inside IC might become weaker and be destroyed.

It is recommended to take into consideration thermal of IC.

Note that the temperatures are in the allowed temperature limits and operated within Pd.

It is necessary to operate it at junction temperature Tjmax or less to prevent IC from the thermal destruction.

Please operate IC within permissible loss Pd because the junction temperature Tj might become considerably a high

temperature even if ambient temperature Ta is normal temperature (25℃).

Power consumption Pc(W) may be expressed by the equation shown below:

Pc=(Vin-Vo)×Io+ Vin×Iｂ

permissible loss Pd≧Pc

・Calculation example

Ex.1)

Ta=85℃, Vin =7.5V, Vo=5.0V

Io≦400ｍA

Be sure to use this IC within a power dissipation at the range of operating temperature.

Fig.25

Thermal derating curve (TO220CP-3)

Fig.26

Thermal derating curve (TO252-3)

●Terminal Setting and Cautions

・INPUT

It is recommended that a capacitor (about 0.33uF) be inserted between INPUT and COMMON.

The value of capacitor is designed suitable for the actual application.

・OUTPUT

It is recommended that a capacitor (about 0.1uF) be inserted between OUTPUT and COMMON.

A tantalum capacitor can also be used for this pin because insufficient capacitors may cause oscillation by a temperature

change.

・COMMON

Keep the no voltage drop between Ground level of set board and IC.

When there is the voltage difference, setting voltage becomes inaccuracy and unstable.

It is recommended to connect by wide, short pattern, and lower the inpedance.

Vo

Vin

Ib

Vin

Pd

Io







≦

5.0

7.5

4.5m

7.5

1.04

Io







≦

Vin : Input Voltage

Vo

: Output Voltage

Io

: Output Current

Ib

: Bias current

Using TO220CP-3 alone

θja=62.5℃/W→16mW/℃

Pd=1.04W at 85℃

12.5

10

7.5

5

2.5

0

0

25

50

75

125

100

150

AMBIENT TEMPERATURE : Ta[℃]

(2) 1.0

(1) 10.0

25

20

15

10

5

0

0

25

50

75

125

100

150

AMBIENT TEMPERATURE : Ta[℃]

(2) 2.0

(1) 22.0

(1) Mounted on infinity Alminium heat sinkθj-c=5.7(℃/W)

(2) Using an IC aloneθj-a=62.5℃/W