Technical Note

BA10393F,BA10339F/FV,BA2903SF/FV/FVM,BA2903F/FV/FVM，

BA2903HFVM-C,BA2901SF/FV/KN,BA2901F/FV/KN

16/19

www.rohm.com

2010.05 - Rev.B

© 2010 ROHM Co., Ltd. All rights reserved.

●Derating curves

Power dissipation(total loss) indicates the power that can be consumed by IC at Ta=25℃(normal temperature).IC is heated

when it consumed power, and the temperature of IC chip becomes higher than ambient temperature.The temperature that

can be accepted by IC chip depends on circuit configuration, manufacturing process, and consumable power is limited.

Power dissipation is determined by the temperature allowed in IC chip(maximum junction temperature) and thermal resistance

of package(heat dissipation capability). The maximum junction temperature is typically equal to the maximum value in the

storage temperature range. Heat generated by consumed power of IC radiates from the mold resin or lead frame of the

package. The parameter which indicatesthis heat dissipation capability(hardness of heat release)is called thermal resistance,

represented by the symbol

θja[℃/W].The temperature of IC inside the package can be estimated by this thermal resistance.

Fig.91(a) shows the model of thermal resistance of the package. Thermal resistance

θja, ambient temperature Ta, junction

temperature Tj, and power dissipation Pd can be calculated by the equation below:

θja ＝ (Tj-Ta) / Pd

[℃/W]

・・・・・

(Ⅰ)

Derating curve in Fig.91(b) indicates power that can be consumed by IC with reference to ambient temperature. Power that can

be consumed by IC begins to attenuate at certain ambient temperature. This gradient iis determined by thermal resistance

θja.

Thermal resistance

θja depends on chip size, power consumption, package,ambient temperature, package condition, wind

velocity, etc even when the same of package is used. Thermal reduction curve indicates a reference value measured at a

specified condition. Fig.92(a)～(d) show a derating curve for an example of BA10393, BA10339, BA2903S, BA2903,

BA2903HFVM-C,BA2901S, BA2901.

（*5）

（*6）

（*7）

（*8）

（*9）

（*10）

（*11）

（*12）

（*13）

Unit

6.2

7.0

4.9

6.2

5.5

4.7

7.0

5.3

4.9

[mW/℃]

When using the unit above Ta=25[℃], subtract the value above per degree[℃]. Permissible dissipation is the value

when glass epoxy board 70[mm]×70[mm]×1.6[mm](cooper foil area below 3[%]) is mounted.

Fig.92

Derating curve

(a) Thermal resistance

(b) Derating curve

Fig.91

Thermal resistance and derating curve

0

50

75

100

125

150

25

P1

P2

Pd (max)

LSI

の消費電力 [W]

θ' ja2

θ' ja1

Tj ' (max)

θja2 < θja1

周囲温度 Ta [℃ ]

θ ja2

θ ja1

Tj (max)

Power dissipation of LSI

Ambient temperature

周囲温度 Ta [℃]

チップ 表面温度 Tj [℃]

消費電力 P [W]

θja = ( Tj ーTa ) / Pd [℃/W]

Chip surface temperature

Power dissipation

Ambient temperature

0

200

400

600

800

1000

0

25

50

75

100

125

0

200

400

600

800

1000

0

25

50

75

100

125

周囲温度　Ta　 [°C]

0

200

400

600

800

1000

0

25

50

75

100

125

150

周囲温度　Ta　 [°C]

0

200

400

600

800

1000

0

25

50

75

100

125

150

周囲温度　Ta　 [°C]

(a)BA10393 family

(b)BA10339 family

(c)BA2903 family

(d)BA2901 family

620mW(

700mW(

490mW(

780mW(

690mW(

590mW(

870mW(

660mW(

610mW(

BA10393F

BA10339FV

BA10339F

BA2903FV

BA2903FVM

BA2903HFVM－C

BA2901FV

BA2901F

BA2903SFV

BA2903SF

BA2903SFVM

BA2901SFV

BA2901SKN

BA2901SF

105

105

Ambient temperature ：Ta [℃]

Ambient temperature ：Ta [℃]

Ambient temperature ：Ta [℃]

Ambient temperature ：Ta [℃]