Stabilizing Fast Transient Response Power Supply/Load Circuits

Keithley’s Series 2300 Battery/Charger Simulators (fast transient response power supplies) are specifically designed for powering RFIC power amplifiers, mobile phone handsets, and other portable, battery-operated products in R&D and manufacturing environments. These battery-simulating power supplies are designed to recover very quickly from short-duration pulse load current changes as large as 1000% (i.e., a 10× increase in load current) and to measure the peak of the load current pulse. In order to maintain the output voltage at the programmed output level despite near instantaneous pulse load changes and to capture information on pulses as short as 600μs, the power supply must combine a fast voltage recovery time with minimal voltage droop from the transient perturbation caused by the fast load current change. Power supplies like the Series 2300 battery/charger simulators must have a fast-responding, wide-bandwidth (beyond 200kHz and up to 2MHz) output stage. While this wide-bandwidth supply recovers quickly from large load current changes, the wide-bandwidth output stage is much more susceptible to the impedance of the external load circuit than conventional narrow-bandwidth DC power supplies. Certain high reactance load conditions, such as long wire runs and capacitive loads with low equivalent series resistance (ESR), can cause the power supply output to begin oscillating. This paper will describe the various load circuit conditions that can cause oscillation and provide methods for stabilizing the load circuit.