An Accurate Digital Inductor Current Sensor for Current-Ripple-Based DC-DC Converters

This paper presents a digital current sensor for digitally-controlled current-ripple-based DC-DC buck converters to estimate the instantaneous inductor-current ripple accurately in both the Discontinuous (DCM) and Continuous (CCM) Current Modes. The current sensor employs a proposed dual-mode input multiplexing technique to select an appropriate representation of the pertinent voltage of the switching node
$(\boldsymbol{V}_{\boldsymbol{x}})$
in any mode, thereby allowing the current to be estimated more accurately compared to that of the prior-art design. The accurate inductor-current ripple information enables the controller to yield output-voltage transient response with small overshoot or undershoot (OS/US) and fast settling time. Benchmarking results using a digitally-controlled current-ripple constant on-time DC-DC buck converter show that the converter employing the proposed sensor achieves
$\geq \mathbf{49}{\%}$
smaller OS/US and
$\geq \mathbf{45}{\%}$
faster settling time at the output voltage in both the DCM and the CCM collectively compared with that of the same converter but with the prior-art sensor.