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A High-Frequency Small-Signal Model for Inverse-Charge Constant On-time (IQCOT) Current-Mode Control

Fig. 1. Considering current feedback as a single entity to model the proposed non-ripple-based IQCOT Control with Vc perturbation.
The control-to-output transfer function can be calculated as:
For low duty cycle (D), the Ton-related double pole will be at a very high frequency and ex-pression:
As the expression of the quality factor of the double pole is a function of duty cycle (D), the Q value will change as the duty cycle changes, which may make the control loop more chal-lenging to design for small-signal stability. To solve this issue, an auto-tuning method is pro-posed to achieve a constant Q value. For example, to keep Q"2 = 1 for operation with a low duty cycle, the quality factor (Q) expression can be rewritten as:
Therefore, to keep Q"2 =1, the control needs to maintain
Details are presented in the conference paper.
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