Technical Note

11/16

BA2904YF-C,BA2904YFVM-C,BA2902YF-C,BA2902YFV-C

www.rohm.com

2011.08 - Rev.B

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

0

200

400

600

800

1000

0

25

50

75

100

125

150

AMBIENT TEMPERATURE [℃]

0

200

400

600

800

1000

0

25

50

75

100

125

150

AMBIENT TEMPERATURE [℃]

●

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.54(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.54(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.55(c),(d) show a derating curve

for an example of BA2904Y, BA2902Y.

(*6)

(*7)

(*8)

(*9)

Unit

6.2

4.8

7.0

4.9

[mW/℃]

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

Permissible dissipation is the value when FR4 glass epoxy board 70[mm]×70[mm]×1.6[mm](cooper foil area below 3[%]) is mounted.

Fig. 55

Derating curve

(a) Thermal resistance

(b) Derating curve

Fig. 54 Thermal resistance and derating

θja = ( Tj ーTa ) / Pd [℃/W]

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)

周囲温度 Ta [℃]

チップ 表面温度 Tj [℃]

消費電力 P [W]

Ambient temperature

Chip surface temperature

Power dissipation Pd[W]

Power dissipation of LSI

Ambient temperature

(c) BA2904Y family

(d) BA2902Y family

BA2904YF-C

BA2904YFVM-C

BA2902YFV-C

BA2902YF-C

780mW(*6)

590mW(*7)

870mW(*8)

610mW(*9)