BU7271G_13 Datasheet, PDF (14/22 Pages) Rohm – Ultra Low Supply Current CMOS Operational Amplifiers

BU7271G BU7271SG
Datasheet
Power Dissipation
Power dissipation (total loss) indicates the power that the IC can consume at T_A=25°C (normal temperature). As the IC
consumes power, it heats up, causing its temperature to be higher than the ambient temperature. The allowable
temperature that the IC can accept is limited. This depends on the circuit configuration, manufacturing process, and
consumable power.
Power dissipation is determined by the allowable temperature within the IC (maximum junction temperature) and the
thermal resistance of the package used (heat dissipation capability). Maximum junction temperature is typically equal to the
maximum storage temperature. The heat generated through the consumption of power by the IC radiates from the mold
resin or lead frame of the package. Thermal resistance, represented by the symbol θ_JA°C/W, indicates this heat dissipation
capability. Similarly, the temperature of an IC inside its package can be estimated by thermal resistance.
Figure 31(a) shows the model of the thermal resistance of the package. The equation below shows how to compute for the
Thermal resistance (θ_JA), given the ambient temperature (T_A), maximum junction temperature (T_Jmax), and power dissipation
(P_D).
θ_JA = (T_Jmax-T_A) / P_D °C/W
The Derating curve in Figure 31(b) indicates the power that the IC can consume with reference to ambient temperature.
Power consumption of the IC begins to attenuate at certain temperatures. This gradient is determined by Thermal
resistance (θ_JA), which depends on the chip size, power consumption, package, ambient temperature, package condition,
wind velocity, etc. This may also vary even when the same of package is used. Thermal reduction curve indicates a
reference value measured at a specified condition. Figure 31. (c) and (d) shows the derating curve for BU7271G and
BU7271SG.
θ_JA=(T_Jmax-T_A)/P_D C/W
Ambient temperature TA[ C ]
Power dissipation of LSI [W]
P_Dmax
P2
θ_JA2 <θ_JA1
P1
θ_JA2
θ_JA1
T_Jmax
Chip surface temperature T_J [C]
(a) Thermal resistance
0
25
50
75
100
125
Ambient temperature T_A[C]
(b) Derating curve
0.8
0.8
0.6
0.6
BU7271G
0.4
0.4
BU7271SG
0.2
0.2
0.0
0
85
25
50
75 100 125
Ambient Temperature [°C]
0.0
0
105
25
50
75 100 125
Ambient Temperature [°C]
(c) BU7271G
(d) BU7271SG
5.4
mW/°C
When using the unit above T_A=25°C, subtract the value above per Celsius degree. Permissible dissipation is the value
when FR4 glass epoxy board 70mm×70mm×1.6mm (copper foil area less than 3%) is mounted
Figure 31. Thermal Resistance and Derating Curve
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TSZ02201-0RAR1G200290-1-2
19.Sep.2013 Rev.001