1 Introduction

The OPA593 is a high-voltage, high-output-current power amplifier (PA) that operates on an 85V single supply or a ±42.5V dual-supply configuration, with the capability to source or sink current up to ±250mA. This article focuses on dual-supply rail configurations, favored for their programmable and flexible precision voltage regulator setups commonly used in automated test equipment (ATE) applications. While the OPA593 meets the output voltage requirements for most power voltage regulator applications, OPA593 does not provide sufficient current drive in certain scenarios. In such cases, combining the OPA593 with a current booster topology can enhance the current drive capabilities while maintaining the amplifier’s overall operating voltage range, bandwidth, accuracy, and responsiveness to timing requirements.

In practice, a large capacitive load is often connected to the output of a power amplifier stage. Capacitive loads serve several purposes, including decoupling, filtering high-frequency noise, reducing voltage spikes, stabilizing transient responses, and improving output voltage regulation at the device under test (DUT). However, adding capacitive loads can introduce undesirable phase lag, potentially leading to loop instability in the power amplifier's feedback system.

Driving large capacitive loads presents significant design challenges for engineers, particularly in compensating for stability issues. This application note addresses these challenges when using the OPA593 with a Darlington current booster configuration. The document also explores the trade-offs associated with this technique, especially when driving capacitive loads up to 1µF.

Figure 1-1 and Table 2-2 present the schematic discussed in this application note, which aims to meet (or exceed) the design requirements.

Figure 1-1 The OPA593 With a Current Booster Circuit Drives 1μF Capacitive Load, C_L