Datasheet OPA2544 (Texas Instruments) - 7

APPLICATIONS INFORMATION
The safe output current decreases as VCE increases. Output short-circuit is a very demanding case for SOA. A short- Figure 1 shows the OPA2544 connected as a basic non- circuit to ground forces the full power supply voltage (V+ inverting amplifier. The OPA2544 can be used in virtually or V–) across the conducting transistor. With V = ±35V S any op amp configuration. Power supply terminals should be the safe output current is 1.5A (at 25°C). The short-circuit bypassed with low series impedance capacitors. The tech- current is approximately 4A which exceeds the SOA. This nique shown, using a ceramic and tantalum type in parallel, situation will activate the thermal shutdown circuit in the is recommended. Power supply wiring should have low OPA2544. For further insight on SOA, consult AB-039. series impedance and inductance.
CURRENT LIMIT
+35V The OPA2544 has an internal current limit set for approxi- V+ mately 4A. This current limit decreases with increasing 10µF junction temperature as shown in the typical curve, Current R G = 1+ = 3 2 + R Limit versus Temperature. This, in combination with the 1 0.1µF thermal shutdown circuit, provides protection from many R R types of overload. It may not, however, protect for short- 1 2 5kΩ 10kΩ circuit to ground, depending on the power supply voltage, ambient temperature, heat sink and signal conditions.
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POWER DISSIPATION OPA2544
VIN Z Power dissipation depends on power supply, signal and load 0.1µF L conditions. For DC signals, power dissipation is equal to the product of output current times the voltage across the con- 10µF + ducting output transistor. Power dissipation can be mini- mized by using the lowest possible power supply voltage necessary to assure the required output voltage swing. V– –35V For resistive loads, the maximum power dissipation occurs at a DC output voltage of one-half the power supply voltage. FIGURE 1. Basic Circuit Connections. Dissipation with AC signals is lower. Application Bulletin AB-039 explains how to calculate or measure power dissi-
SAFE OPERATING AREA
pation with unusual signals and loads. Stress on the output transistors is determined by the output current and the voltage across the conducting output transis-
HEATSINKING
tor, V . The power dissipated by the output transistor is CE Most applications require a heat sink to assure that the equal to the product of the output current and the voltage maximum junction temperature is not exceeded. The heat across the conducting transistor, V . The Safe Operating CE sink required depends on the power dissipated and on Area (SOA curve, Figure 2) shows the permissible range of ambient conditions. Consult Application Bulletin AB-038 voltage and current. for information on determining heat sink requirements. The heat sink tab of the plastic package is connected to the V– power supply terminal. Lowest thermal resistance can be SAFE OPERATING AREA achieved by mounting the tab directly to a heat sink. If the 10 heat sink cannot be electrically “hot” at V– power supply Current-Limited potential, insulating hardware must be used. 4 T = 25°C C Output current may
THERMAL PROTECTION
be limited to less 1 The OPA2544 has thermal shutdown that protects the ampli- than 4A—see text. fier from damage. Any tendency to activate the thermal T = 85°C C Output Current (A) 0.4 shutdown circuit during normal operation is indication of excessive power dissipation or an inadequate heat sink. T = 125°C C The thermal protection activates at a junction temperature 0.1 of approximately 155°C. For reliable operation, junction 1 2 5 10 20 50 100 temperature should be limited to 150°C, maximum. To |V – V | (V) S O estimate the margin of safety in a complete design (includ- ing heat sink), increase the ambient temperature until the FIGURE 2. Safe Operating Area. thermal protection is activated. Use worst-case load and signal conditions. For good reliability, the thermal protec- ® 7
OPA2544