A 10MHz, 40V-to-5V clock-synchronized AOT hysteretic converter with programmable soft start technique for automotive USB chargers

Adaptive on-time (AOT) hysteretic control has gained increasing popularity in automotive electronics, because of its superior line regulation and fast load transient response. However, it faces serious switching frequency deviation and soft start issues from the conventional implementations. To mitigate these, this paper proposes a clock-synchronized AOT hysteretic control which adaptively synchronizes the switching converter to a desirable reference frequency without degrading its line regulation and load transient response. Meanwhile, a programmable soft start modulator is proposed to allow reliable start-up in heavy load condition and prevent large inrush current from damaging the power devices. Designed on a high voltage (HV) 0.35μm BCD process, the integrated converter achieves a single-stage 40V to 5V voltage conversion with a full load of 15W and a peak efficiency of 90.5%. With the proposed clock-synchronized Ton timer, the switching frequency is maintained at a fixed 10MHz, over the full input, output and load ranges. The programmable soft start modulator achieves 100μs to 6ms soft start time, which greatly suppresses startup inrush current.