Integration of loop gain measurement circuit for stability evaluation in DC/DC converters with time-based control

The crossover frequency of DC/DC converters is related to some key dynamic performances such as line and load transient response. In integrated converters, its experimental measurement using standard techniques requires the connection to internal nodes of the controller that are not always accessible to the user. This paper presents a novel integrated loop gain measurement circuit for DC/DC converters with time-based control. The proposed circuit requires only two current-controlled delay lines, a transconductor, and two flip-flops that can be easily integrated with limited area occupation. An analytic description that relates the circuit parameters with the loop gain transfer function is provided along with some design rules for the transistor-level implementation. A prototype of the loop gain measurement circuit has been embedded in a DC/DC boost converter with time-based control designed in a BCD technology with 180 nm CMOS. The circuit has an area occupation of 0.027 mm2 with a current consumption of a few tens of μA.