Buck-Boost Error Amplifier Layout for CV/CC Mode Accuracy
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Solution Overview
Problem
Integrated circuits (ICs) controlling USB power delivery face challenges in maintaining accurate voltage regulation and preventing overlap between constant voltage and constant current control regions, leading to inaccuracy and early saturation, especially when operating near the border region of these modes.
Innovation Solution
The implementation of a buck-boost converter architecture with a pair of transconductance amplifiers and additional circuitry such as offset cancellation, dynamic current sourcing, and transconductance boosting, which allows for independent control of bandwidth in both constant voltage and constant current modes, minimizing offset and overlap regions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single control amplifier is used for both constant voltage and constant current modes, then device complexity is reduced, but control accuracy deteriorates due to overlap regions and early saturation
Solution Approach 1:
The patent divides the control function into two separate transconductance amplifiers: a first transconductance amplifier dedicated to constant voltage mode and a second transconductance amplifier dedicated to constant current mode. This segmentation eliminates the overlap region between control modes and prevents early saturation, thereby improving voltage regulation accuracy while maintaining reasonable device complexity through systematic functional division.
2Speed
If the bandwidth is optimized for one mode, then transient response in that mode is improved, but performance in the other mode deteriorates
Solution Approach 1:
The patent implements independent bandwidth configuration for each transconductance amplifier, allowing the first amplifier (constant voltage mode) and the second amplifier (constant current mode) to have different bandwidth settings. This dynamic adaptability enables optimization of transient response for each operating mode separately, with the first amplifier having a first bandwidth and the second amplifier having a second bandwidth, thereby achieving versatile performance across different operational conditions.
3Measurement precision
If offset cancellation circuitry is added, then voltage regulation accuracy is improved, but device complexity increases
Solution Approach 1:
The patent incorporates offset cancellation circuitry that proactively compensates for input offset voltages before they affect the control accuracy. By implementing preliminary offset cancellation in both transconductance amplifiers, the system prevents accuracy degradation from occurring in the first place, thereby improving voltage regulation precision while keeping the additional circuit complexity manageable through targeted rather than comprehensive compensation.
Data Source
AI summary
An error amplifier includes an output pin coupled to a pulse width modulation (PWM) comparator of a buck-boost converter. A first transconductance amplifier adjusts an output current at the output pin and operates in a constant voltage mode. The first transconductance amplifier includes a first positive input to receive a first voltage reference and a first negative input coupled to a tap point of a voltage divider coupled between a voltage bus and a ground of the buck-boost converter. A second transconductance amplifier also adjusts the output current at the output pin and operates in a constant current mode. The second transconductance amplifier includes a second positive input to receive a second voltage reference and a second negative input coupled to a current sense amplifier, the current sense amplifier being coupled to a sense resistor positioned inline along the voltage bus.