Switching Regulator Capacitor Current Estimation
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Solution Overview
Problem
Conventional switching regulators experience high latency and ring back due to low inductor current sampling rates, leading to unfavorable voltage responses during load changes, which is costly and power-intensive to address with high-performance current ADCs.
Innovation Solution
The method involves controlling a switching regulator's power stage via PWM signals, sampling the inductor current at a lower rate than the load voltage, estimating the capacitor current based on the sampled load voltage, and adjusting the PWM signal with an offset generated from the inductor and capacitor currents to enhance transient response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If high-performance current ADCs with high sampling rates are used, then the voltage response speed and transient performance are improved, but the cost, chip area, and power consumption increase
Solution Approach 1:
The patent creates a digital model (copy) of the output capacitor current based on the relationship between inductor current and capacitor current. Instead of directly measuring capacitor current with high-speed ADCs, the system uses the already-sampled inductor current to estimate capacitor current through mathematical modeling, achieving the same control objective with lower power consumption and cost
Solution Approach 2:
The patent replaces the physical measurement system (current ADCs) with a computational approach. By substituting hardware-based current sensing with software-based current estimation using mathematical models and digital signal processing, the system achieves equivalent performance while reducing power consumption and eliminating the need for additional high-performance ADC components
2Device complexity
If inductor current is sampled at a lower rate, then the system complexity and power consumption are reduced, but the voltage response introduces high latency and causes ring back
Solution Approach 1:
The patent pre-calculates and stores the relationship between inductor current and capacitor current in digital form during the design phase. This preliminary modeling work allows the system to quickly estimate capacitor current from inductor current samples without requiring complex real-time calculations, thereby reducing control latency while maintaining low sampling rates
Solution Approach 2:
The patent introduces a digital model as an intermediary between inductor current sampling and capacitor current estimation. This mathematical model acts as a bridge that translates low-rate inductor current samples into accurate capacitor current estimates, enabling fast response without requiring high sampling rates or complex hardware
3Reliability
If AVP loops with high sampling rates are used, then the voltage excursions are minimized, but the latency in the control system increases due to processing overhead
Solution Approach 1:
The patent creates a digital copy of the capacitor current waveform based on the inductor current measurement and their known relationship. This copied signal can be processed and applied to the control loop without the latency associated with direct high-rate sampling and processing of actual capacitor current, maintaining voltage stability while reducing control latency
Data Source
AI summary
A switching regulator includes a controller and a power stage for coupling to a load through an inductor and a capacitor. The a controller is operable to control operation of the power stage via a pulse width modulation (PWM) signal generated based on a difference between a reference voltage and the load voltage and sample the inductor current at a lower rate than the load voltage. The controller is further operable to estimate the capacitor current based on the sampled load voltage, generate an offset to the reference voltage based on the sampled inductor current and the estimated capacitor current and adjust the PWM signal applied to the power stage based on the offset. The switching regulator can be single-phase or multi-phase.