Datasheet

POWER DISSIPATION HEATSINKING
T =T +P q
J A D JA
(1)
0 0.5 1.0 1.5 2.0 2.5 3.0
CopperArea(inches ),2oz
2
ThermalResistance, q °
JA
( C/W)
60
50
40
30
20
10
0
OPA454
R
100kW
1
ComplianceVoltageRange=+47V, 48V-
+50V
R
10kW
2
R3
100kW
R
9.9kW
4
-50V
R
100W
5
I
L
R
L
I =[(V - V )/R ](R /R )
=(V V )/1k- W
L 5 2 1
2 1
2 1
V
2
V
1
-IN
+IN
V-
V+
V
OUT
OPA454
www.ti.com ....................................................................................................................................... SBOS391A – DECEMBER 2007 – REVISED DECEMBER 2008
Power dissipation depends on power supply, signal, Power dissipated in the OPA454 causes the junction
and load conditions. For dc signals, power dissipation temperature to rise. For reliable operation, junction
is equal to the product of the output current times the temperature should be limited to +125 ° C, maximum.
voltage across the conducting output transistor, Maintaining a lower junction temperature always
P
D
= I
L
(V
S
– V
O
). Power dissipation can be results in higher reliability. Some applications require
minimized by using the lowest possible power-supply a heatsink to assure that the maximum operating
voltage necessary to assure the required output junction temperature is not exceeded. Junction
voltage swing. temperature can be determined according to
Equation 1 :
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
Package thermal resistance, θ
JA
, is affected by
lower because the root-mean square (RMS) value
mounting techniques and environments. Poor air
determines heating. Application Bulletin SBOA022
circulation and use of sockets can significantly
explains how to calculate or measure dissipation with
increase thermal resistance to the ambient
unusual loads or signals. For constant current source
environment. Many op amps placed closely together
circuits, maximum power dissipation occurs at the
also increase the surrounding temperature. Best
minimum output voltage, as Figure 69 shows.
thermal performance is achieved by soldering the op
amp onto a circuit board with wide printed circuit
The OPA454 can supply output currents of 25mA and
traces to allow greater conduction through the op
larger. Supplying this amount of current presents no
amp leads. Increasing circuit board copper area to
problem for some op amps operating from ± 15V
approximately 0.5in
2
decreases thermal resistance;
supplies. However, with high supply voltages, internal
however, minimal improvement occurs beyond 0.5in
2
,
power dissipation of the op amp can be quite high.
as shown in Figure 70 .
Operation from a single power supply (or unbalanced
power supplies) can produce even greater power
For additional information on determining heatsink
dissipation because a large voltage is impressed
requirements, consult Application Bulletin SBOA021
across the conducting output transistor. Applications
(available for download at www.ti.com ).
with high power dissipation may require a heatsink, or
heat spreader.
Figure 70. Thermal Resistance versus Circuit
Board Copper Area
NOTE: R
1
= R
3
and R
2
= R
4
+ R
5
.
Figure 69. Precision Voltage-to-Current Converter
with Differential Inputs
Copyright © 2007 – 2008, Texas Instruments Incorporated Submit Documentation Feedback 21
Product Folder Link(s): OPA454