OPA454_16 Datasheet, PDF (36/47 Pages) Texas Instruments – High-Voltage (100-V), High-Current (50-mA) Operational Amplifiers

OPA454
SBOS391B – DECEMBER 2007 – REVISED MARCH 2016
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12.3 Thermal Protection
Figure 86 shows the thermal shutdown behavior of a socketed OPA454 that internally dissipates 1 W.
Unsoldered and in a socket, θ_JA of the DDA package is typically 128°C/W. With the socket at 25°C, the output
stage temperature rises to the shutdown temperature of 150°C, which triggers automatic thermal shutdown of the
device. The device remains in thermal shutdown (output is in a high-impedance state) until it cools to 130°C
where it again is powered. This thermal protection hysteresis feature typically prevents the amplifier from leaving
the safe operating area, even with a direct short from the output to ground or either supply. The rail-to-rail supply
voltage at which catastrophic breakdown occurs is typically 135 V at 25°C. However, the absolute maximum
specification is 120 V, and the OPA454 must not be allowed to exceed 120 V under any condition. Failure as a
result of breakdown, caused by spiking currents into inductive loads (particularly with elevated supply voltage), is
not prevented by the thermal protection architecture.
40
140
20
120
V_OUT
0
100
-20
80
-40
60
-60
40
-80
20
V_FLAG
-100
0
-120
0
-20
200
400
600
800
1000
(ms)
+2.5V
10Hz Square Wave
10kW
100kW
+50V
R_P
1MW
-IN ^V+
+IN ^OPA454
Flag
V_OUT
V_FLAG
E/D Com
V-
V_OUT
625W
-50V
Figure 86. Thermal Shutdown
12.4 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 87
shows.
The OPA454 can supply output currents of 25 mA and larger. Supplying this amount of current presents no
problem for some op amps operating from ±15-V 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 a heat spreader.
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