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Model for Constant On-time V2 Control with Combination of Various Types of Output Capacitors

Fig. 1. Control signal to output voltage transfer function.
Constant on-time V2 control is used more and more widely in point of load converters. Previously in CPES a new modeling strategy based on time-domain describing has been proposed for V2 control. However, previous modeling result can only apply to V2 control with single type of output capacitors, such as all OSCON caps or all ceramic caps. To model V2 control with cap combination case, ESR of the ceramic capacitors is ignored and the output voltage time domain waveform is examined with great detail. Using describing function method, effect coming from cap combination can be identified.

Fig. 2. Constant on-time V2 control with cap combination.
Fig. 3. Time domain waveform of output voltage.
Fig. 4. Transfer function from control to output voltage (D=0.1, Fsw=300kHz,RC1=3m, Co1=660uF, Co2=300uF).
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