1 Introduction

The OPA593 high-voltage, high-current operational amplifier (op amp) is finding design-in opportunities in different test platforms and applications. The 85 V single, ±42.5 V dual-supply capability, 0.25-A maximum output drive current, and accurate current limit set (Iset) make it a good match for semiconductor and other component tester applications. Such applications often require rapid supply voltage and load current changes through the test cycle.

Recently, a new test application surfaced from the field that not only required the OPA593 high output voltage capability, but also high output current up to 0.5 A. This is double the normal 0.25-A output load current capability. A single OPA593 device is not able to provide the higher current level, but a pair of OPA593 amplifiers with their outputs connected in a parallel does. It is often assumed that paralleling op amps is an easy thing to do, but then the performance proves to be less than expected in one way or another. However, by applying careful attention to design details such as current balancing, good performance can be achieved.

Parallel output circuits often appear in the application section of the data sheet for a power op amp. Two commonly-shown configurations include a simple parallel-connected pair of op amps seen in Figure 1-1, and a bit more sophisticated Leader-follower circuit shown in Figure 1-2. Both circuits incorporate output ballast resistors, Rb1 and Rb2 that play an important role in the operation of each circuit. The selection of these circuits is discussed in this document. The Leader-follower circuit is more often applied because it provides accurate voltage output Vo level whereas the output of the simple circuit changes with load.