OPA454 Datasheet, PDF (21/36 Pages) Texas Instruments – High-Voltage (100V), High-Current (50mA) OPERATIONAL AMPLIFIERS, G = 1 Stable

OPA454
www.ti.com
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 because the root-mean square (RMS) value
determines heating. Application Bulletin SBOA022
explains how to calculate or measure dissipation with
unusual loads or signals. For constant current source
circuits, maximum power dissipation occurs at the
minimum output voltage, as Figure 69 shows.
The OPA454 can supply output currents of 25mA and
larger. Supplying this amount of current presents no
problem for some op amps operating from ±15V
supplies. However, with high supply voltages, internal
power dissipation of the op amp can be quite high.
Operation from a single power supply (or unbalanced
power supplies) can produce even greater power
dissipation because a large voltage is impressed
across the conducting output transistor. Applications
with high power dissipation may require a heatsink, or
heat spreader.
R₁
100kW
V₁
R3
100kW
V₂
R₂
10kW
+50V
-IN
V+
V_OUT
OPA454
+IN
V-
R₄
-50V ^9.9kW
R₅
100W
I_L
R_L
I_L = [(V₂ - V₁)/R₅] (R₂/R₁)
= (V₂ - V₁)/1kW
Compliance Voltage Range = +47V, -48V
NOTE: R₁ = R₃ and R₂ = R₄ + R₅.
Figure 69. Precision Voltage-to-Current Converter
with Differential Inputs
SBOS391 – DECEMBER 2007
HEATSINKING
Power dissipated in the OPA454 causes the junction
temperature to rise. For reliable operation, junction
temperature should be limited to +125°C, maximum.
Maintaining a lower junction temperature always
results in higher reliability. Some applications require
a heatsink to assure that the maximum operating
junction temperature is not exceeded. Junction
temperature can be determined according to
Equation 1:
T_J = T_A + P_D q_JA
(1)
Package thermal resistance, θ_JA, is affected by
mounting techniques and environments. Poor air
circulation and use of sockets can significantly
increase thermal resistance to the ambient
environment. Many op amps placed closely together
also increase the surrounding temperature. Best
thermal performance is achieved by soldering the op
amp onto a circuit board with wide printed circuit
traces to allow greater conduction through the op
amp leads. Increasing circuit board copper area to
approximately 0.5in² decreases thermal resistance;
however, minimal improvement occurs beyond 0.5in²,
as shown in Figure 70.
For additional information on determining heatsink
requirements, consult Application Bulletin SBOA021
(available for download at www.ti.com).
60
50
40
30
20
10
0
0
0.5
1.0
1.5
2.0
2.5
3.0
Copper Area (inches²), 2 oz
Figure 70. Thermal Resistance versus Circuit
Board Copper Area
Copyright © 2007, Texas Instruments Incorporated
Product Folder Link(s): OPA454
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