OPA445BM Datasheet, PDF (11/25 Pages) Texas Instruments – High Voltage FET-Input OPERATIONAL AMPLIFIER

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100
1in x 0.5in, 1oz Cu
10
T_A = 25_ C
T_A = 85_ C
T_A = 120_C
1
T_A + [(|V_S| − |V_O|) I_O × θ_JA] ≤ T_J (max)
θ _JA = 52_C/W
T_J (max) = 125_ C
0.1
1
10
100
|V_S| − |V_O| (V)
Figure 10. SO-8 PowerPAD Safe Operating Area
(with heat-spreader, no airflow)
120
100
No Heat−Spreader
80
60
With Heat−Spreader, 1in x 0.5in, 1oz Cu
40
20
0
0
0.5
1.0
1.5
2.0
2.5
3.0
Air−Flow (meters/sec)
Figure 11. SO-8 PowerPAD Thermal Resistance
(with and without heat-spreader)
100
No Airflow
90
80
70
60
50
40
30
0
0.5
1.0
1.5
2.0
2.5
3.0
Copper Area (inches²)
Figure 12. Thermal Resistance vs Circuit Board
Copper Area
OPA445
SBOS156B − MARCH 1987 − REVISED APRIL 2008
POWER DISSIPATION
Power dissipation depends on power supply, signal, and
load conditions. For dc signals, power dissipation is equal
to the product of the output current times the voltage
across the conducting output transistor, P_D = I_L (V_S − V_O).
Power dissipation can be minimized by using the lowest
possible power-supply voltage necessary to assure the
required output voltage swing.
For resistive loads, the maximum power dissipation occurs
at a dc output voltage of one-half the power supply voltage.
Dissipation with ac signals is lower. Application Bulletin
SBOA022 explains how to calculate or measure
dissipation with unusual loads or signals.
The OPA445 can supply output currents of 15mA and
larger. This would present no problem for a standard op
amp operating from ±15V supplies. With high supply
voltages, however, internal power dissipation of the op
amp can be quite large. Operation from a single power
supply (or unbalanced power supplies) can produce even
larger power dissipation since a large voltage is impressed
across the conducting output transistor. Applications with
large power dissipation may require a heat-sink.
HEAT SINKING
Power dissipated in the OPA445 will cause the junction
temperature to rise. For reliable operation junction
temperature should be limited to 125°C, maximum (150°C
for TO-99 package). Some applications will require a
heat-sink to assure that the maximum operating junction
temperature is not exceeded. In addition, the junction
temperature should be kept as low as possible for
increased reliability. Junction temperature can be
determined according to the following equation:
T_J + T_A ) P_D q_JA
(1)
Package thermal resistance, q_JA, is affected by mounting
techniques and environments. Poor air circulation and use
of sockets can significantly increase thermal resistance.
Best thermal performance is achieved by soldering the op
amp into a circuit board with wide printed circuit traces to
allow greater conduction through the op amp leads.
Simple clip-on heat sinks (such as a Thermalloy 2257) can
reduce the thermal resistance of the TO-99 metal package
by as much as 50°C/W. The SO-8 PowerPAD package will
provide lower thermal resistance, especially with a simple
heat-spreader—even lower with a heat-sink. For
additional information on determining heat-sink require-
ments, consult Application Bulletin SBOA021.
11