A Frequency Stable On-Time Control Buck Converter With Reference and Frequency Compensation Technique Using Low ESR Output Capacitor

Two issues plaguing the on-time control dc–dc buck converter are the system instability caused by low equivalent series resistance (ESR) output capacitor and the great variation on switching frequency caused by input/output voltage and load current. Without additional external components or integrated clock-controlled circuits and RC filters, the reference and frequency compensation (RFC) technique is presented in this article to stabilize the converter and eliminate its switching frequency variation issue with a low ESR output capacitor. The proposed frequency-stable on-time control buck converter with input voltage ranging from 4.5 to 30 V and output load ranging up to 6 A was fabricated using a standard 0.25-
μ
m BCD (BiCMOS/DMOS) process. With a low ESR ceramic output capacitor, the experimental results show that the converter functions properly and stably over the whole load range, and the switching frequency variation with load current is constrained to 3.8 kHz/A, which is a fairly constant value. Moreover, the peak efficiency of the converter is about 98% and the load transient response is also shown excellent performance with the load stepping from 0.1 to 6 A.