Digital Constant On-Time DC-DC Converter Offset Cancellation
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Solution Overview
Problem
Constant on-time (COT) DC-to-DC converters experience output voltage offset errors due to analog ripple-based control schemes, degrading regulation performance.
Innovation Solution
A digital COT controller with a current sensing circuit, offset cancellation circuit, comparator, and PWM generator is used to sense inductor current, remove voltage offset, and generate a switch control signal, effectively canceling output voltage offset by comparing an offset-removed sense voltage with a reference signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If an analog ripple-based control scheme is adopted in a COT DC-to-DC converter, then the converter can operate with constant on-time control, but output voltage offset error is introduced which degrades regulation performance
Solution Approach 1:
The patent extracts and removes the offset component from the sensed inductor current signal. The offset cancellation circuit separates the DC offset component from the AC ripple component, removing only the harmful offset portion while preserving the useful ripple information needed for COT control.
Solution Approach 2:
The patent introduces an offset cancellation circuit as an intermediary between the current sensing circuit and the comparator. This intermediary circuit processes the sensed current signal by subtracting the offset component, providing a cleaned signal to the comparator without affecting the overall COT control operation.
2Ease of operation
If an analog current sensing circuit is used to sense inductor current, then the converter can implement current-based control, but output voltage offset error is introduced that degrades regulation performance
Solution Approach 1:
The offset cancellation circuit extracts and removes the DC offset component from the analog current sensing signal. By taking out only the offset portion while preserving the AC ripple component, the circuit maintains ease of current-based control operation while eliminating the precision-degrading offset error.
Solution Approach 2:
The offset cancellation circuit serves as an intermediary processing stage between the analog current sensor and the control comparator. It mediates the signal by removing the offset component, allowing the system to maintain simple current-based control operation while achieving improved measurement precision.
Data Source
AI summary
A digital constant on-time controller adaptable to a direct-current (DC)-to-DC converter includes a current sensing circuit that senses stored energy of the DC-to-DC converter, thereby generating a sense voltage; an offset cancellation circuit coupled to receive the sense voltage, thereby generating an offset-removed sense voltage according to a valley voltage of the sense voltage; a comparator that compares the offset-removed sense voltage with a reference signal; and a pulse-width modulation (PWM) generator that generates a switch control signal according to a comparison result of the comparator.