Current Sense Amplifier Thermal Calibration for Voltage Converters
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Solution Overview
Problem
Multi-phase converters face challenges in accurately sensing output currents across phases to regulate and balance currents, particularly under varying load conditions and thermal changes, which affects adaptive voltage positioning and overcurrent protection.
Innovation Solution
A current sense amplifier using DCR current sensing with variable gain amplifiers and active offset calibration, along with a thermal calibration circuit, to maintain accurate measurements and compensate for inductor resistance variations with temperature, ensuring continuous calibration and balanced current delivery across channels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If DCR current sensing is used to sense output current, then power loss is reduced compared to using a sensing resistor, but measurement precision deteriorates due to inductor resistance variations with temperature
Solution Approach 1:
The patent implements a dynamic calibration system where the current sense amplifier periodically calibrates its offset voltage and gain factors. The calibration circuit dynamically adjusts the amplifier parameters based on measured inductor resistance variations, allowing the system to adapt to changing thermal conditions while maintaining accurate current sensing without requiring additional sensing components that would increase power loss.
Solution Approach 2:
The patent changes the electrical parameters of the current sense amplifier (offset voltage, gain factors) based on measured inductor resistance variations. By dynamically adjusting these parameters according to temperature-dependent resistance changes, the system maintains measurement precision while continuing to use the low-power DCR sensing method rather than switching to higher-power alternative sensing approaches.
2Measurement precision
If multiple current sense amplifiers are used to monitor each phase, then current balance and regulation are improved, but device complexity increases
Solution Approach 1:
The patent designs a universal current sense amplifier that can monitor multiple phases through sequential switching. The same amplifier circuit is time-multiplexed across different phases, allowing one amplifier to perform the function of multiple amplifiers. This reduces the total number of amplifiers needed while maintaining accurate current balance monitoring for all phases, thereby reducing device complexity without sacrificing measurement precision.
Solution Approach 2:
The patent implements periodic calibration cycles where the current sense amplifier sequentially connects to different phases to perform offset voltage and gain factor calibrations. This periodic action allows a single amplifier to maintain accurate measurement capabilities for multiple phases by refreshing its calibration data regularly, eliminating the need for permanently dedicated amplifiers for each phase and thus reducing overall system complexity.
3Measurement precision
If calibration is performed continuously to compensate for thermal changes, then measurement precision is maintained, but loss of time occurs during calibration cycles
Solution Approach 1:
The patent performs calibration actions in advance during periods when the system is less sensitive to measurement accuracy, such as during light load conditions or transition periods. By proactively updating offset voltage and gain factor calibration data before thermal drift significantly impacts measurement precision, the system maintains accurate current sensing without requiring continuous calibration that would consume excessive time during critical operation periods.
Solution Approach 2:
The calibration circuit operates autonomously using internally generated test signals and automatic feedback mechanisms. The system self-calibrates by measuring its own offset voltages and adjusting its gain factors without requiring external intervention or system shutdown. This self-service calibration minimizes the impact on system operation time while maintaining measurement precision, as the calibration occurs seamlessly during normal operation rather than requiring dedicated calibration time periods.
Data Source
AI summary
A thermal calibration circuit for adjusting the gain of a variable gain amplifier, the thermal calibration circuit comprising an interface for receiving a signal that varies with temperature and for providing a signal related to the variation of the temperature; a variable gain amplifier having an input and an output; the signal related to the variation of the temperature being selectively coupled to the input; a circuit at the output of the variable gain amplifier for developing a first current proportional to a difference between a current developed at the output of the variable gain amplifier and a reference current; and the first circuit driving a further circuit to produce a gain control signal for adjusting the gain of the variable gain amplifier.