BU7291G Datasheet, PDF (24/27 Pages) Rohm – High Speed with Low Voltage CMOS Operational Amplifiers

BU7291G,BU7291SG,BU7255HFV,BU7255SHFV,
BU7495HFV,BU7495SHFV,BU7481G,BU7481SG,BU7485G,BU7485SG,BU5281G,BU5281SG
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.149 (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.149 (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.150(c)-(d) show a derating curve for an example of BU7291 family, BU7255 family, ,
BU7495 family , BU7481 family , BU7485 family , BU5281 family.
θja ₌ (T_－j Ta) / Pd [ _℃ / W]
P2
Ambient temperature Ta[ ℃]
Package face temperature _{Ta[℃ ] P1}
[W]
Pd(max)
θja1
θja2 <θja1
θja2
Tj(max)
Chip surface temperature Tj[ ℃ ]
(a) Thermal resistance
Pd[W]
0
25
50
75
100
125
Ambient temperature Ta[℃]
(b) Derating curve
(a) Thermal reFsigis.1ta4n9cTehermal ^{resistance and derating}
1000
800
5 4 0 [ m W ] ^BU7291G(*20)
BU7481G(*20)
BU7485G(*20)
BU5281G(*20)
1000
800
540[mW]
BU7291SG(*20)
BU7481SG(*20)
BU7485SG(*20)
BU5281SG(*20)
600
5
3
5
[
m
W
]
BU7255HFV(*21)
BU7495HFV(*21)
600
5 3 5 [ m W ] ^{BU7255SHFV(*21)}
BU7495SHFV(*21)
400
400
200
200
0
85
0
50
100
150
AMBIENT TEMPERATURE[℃]
(c) BU7291G BU7481G BU7485G
BU5281G BU7255HFV BU7495HFV
0
105
0
50
100
150
AMBIENT TEMPERATURE[℃]
(d) BU7291SG BU7481SG BU7485SG
BU5281SG BU7255SHFV BU7495SHFV
(*20)
(*21)
Unit
5.4
5.35
[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.150 Derating Curve
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2010.12 - Rev.A