BU7265G_1 Datasheet, PDF (15/18 Pages) Rohm – Ultra Low Power CMOS Operational Amplifiers

BU7265G,BU7265SG,BU7271G,BU7271SG,
BU7411G,BU7411SG,BU7421G,BU7421SG
Technical Note
●Derating Curve
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 ship 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 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 indicates this heat dissipation capability (hardness of heat release) is called
thermal resistance, represented by the symbol θj-a[℃/W]. The temperature of IC inside the package can be estimated by
this thermal resistance.
Fig.98 (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.98 (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 is 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.99(c)-(d) show a derating curve for an example of BU7265 family, BU7271family,
BU7411family, BU7421family.
θja ₌ (T_－j Ta) / Pd [ _℃ / W]
Ambient temperature Ta[ ℃]
Package face temperature _{Ta[℃ ]}
[W]
Pd(max)
P2
P1
θja1
θja2 <θja1
θja2
Tj(max)
Chip surface temperature Tj[ ℃ ]
Power dissipation Pd[W]
0
25
50
75
100
Ambient temperatureTa[℃ ]
(a) Thermal resistance
(b) Derating curve
Fig.98 Thermal resistance and derating
125
150
BU7265/BU7271
BBUU77441111//BBUU77442211
Tj(max)
800
540[mW]
600
800
540ï¼»mWï¼½
600
400
400
200
200
0
0
50
85 ₁₀₀
150
AMBIENT TEMPERATURE [℃]
(c) BU7265G BU7271G
BU7411G BU7421G
0
0
50
100 ¹⁰⁵
150
AMBIENT TEMPERATURE [℃]
(d) BU7265SG BU7271SG
BU7411SG BU7421SG
1/θja
Unit
5.4
[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.99 Derating Curve
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15/17
2010.03 - Rev.A