OPA541

SBOS153B – SEPTEMBER 2000 – REVISED JANUARY 2016

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Typical Applications (continued)

8.2.1.2.3

Heat Sinking

Short circuit conditions at 5 A and 25 V must support 125 W of dissipation up to the 40°C ambient requirements

of the application. This indicates the need for a heatsink with a RθHA < 0.68°C/W, such as an Waekfield-Vette

345 series.

8.2.1.3 Application Curve

The scope trace in Figure 14 depicts a motor reversal of a 20-V motor being driven by an OPA541 powered by

±25 V. This motor has 1

Ω of DC resistance and 10 µH of inductance.

NOTE

At the beginning of the reversal the motor inductance results in an overshoot up to the

supply rail. This overshoot is clamped by the external fast recovery diodes. While the

current shown exceeds the 5-A current limit, this current is actually flowing in the flyback

diodes.

Figure 14. Transient Response

8.2.2 Paralleled Operation, Extended SOA

Parallel operation is often used to increase output current or wattage. However, due to their low output

impedance, power operational amplifiers cannot be connected in parallel without modifying the circuits. Figure 15

shows one method of doing this. The upper amplifier is a master, configured as required to satisfy the circuit

function, has a small sense resistor inside its feedback loop. The slave amplifier is a unity gain buffer. Thus, the

output voltages of the two amplifiers are equal. If the two sense resistors connected to the load are equal, the

amplifiers share current equally. More slaves may be added as desired. The additional resistor and capacitor on

the slave enhance stability.

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