Buck-Boost Converter Current Sensing for Forced CCM Accuracy

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Solution Overview

Problem

Existing DC-DC converters, particularly in AMOLED display panel applications, face challenges with current measurement due to additional quiescent current, increased chip area, and efficiency losses, especially under light loads, and are not compatible with forced Continuous-Conduction Mode operations.

Innovation Solution

A method utilizing an inverting buck-boost converter, sample and hold circuit, and low pass weighted filter to measure high-side switch current, improving accuracy and efficiency while reducing quiescent current consumption and offering tunable solutions for offset cancellation and sensitivity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a current sense is used on a high side switch of a boost converter, then current measurement capability is provided, but additional quiescent current is introduced and chip area footprint increases

Engineering Contradiction:

Improvecurrent measurement capabilityVSAvoidquiescent current

Core Design Contradiction:

Measurement precisionVSUse of energy by stationary object

Solution Approach 1:

The high-side switch serves dual purposes: as the main power switching element and as a current sensing element. By utilizing the existing switch's on-resistance for current measurement, the patent eliminates the need for separate sensing components, thereby reducing quiescent current consumption and chip area while maintaining measurement capability

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The high-side switch's inherent on-resistance is exploited to generate the sensing signal without requiring external sensing components. The switch itself provides the measurement function through its natural electrical properties, eliminating additional power consumption and component requirements

Inventive Principle:

Principle #25Self-service

2Measurement precision

If a current sense is used on a high side switch of a boost converter, then current measurement capability is provided, but chip area footprint increases

Engineering Contradiction:

Improvecurrent measurement capabilityVSAvoidchip area footprint

Core Design Contradiction:

Measurement precisionVSArea of stationary object

Solution Approach 1:

Inventive Principle:

Principle #6Universality (Multi-functionality)

Solution Approach 2:

The patent combines the power switching function and current sensing function into a single component (the high-side switch). This merging eliminates the need for separate sensing resistors or current sense amplifiers, significantly reducing the overall chip area footprint

Inventive Principle:

Principle #5Merging (Combining)

3Measurement precision

If a current sense is used on a high side switch of a boost converter, then current measurement capability is provided, but extra current consumption occurs leading to lower efficiency, especially in presence of a light load

Engineering Contradiction:

Improvecurrent measurement capabilityVSAvoidefficiency

Core Design Contradiction:

Measurement precisionVSLoss of energy

Solution Approach 1:

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The patent uses the existing on-resistance of the switch, which is already present and necessary for normal operation, rather than adding excessive sensing components. This partial utilization of existing properties avoids additional energy loss while providing adequate sensing capability

Inventive Principle:

Principle #16Partial or excessive action

4Measurement precision

If a current sense is used on a high side switch of a boost converter, then current measurement capability is provided, but introduction of error due to unidirectionality of current measurability occurs, hardly compatible with forced CCM operations

Engineering Contradiction:

Improvecurrent measurement capabilityVSAvoidcompatibility with forced CCM operations

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

Instead of using a unidirectional current sense approach, the patent measures the voltage across the high-side switch during its off-state, which indirectly provides bidirectional current information. This inverted measurement approach resolves the unidirectionality limitation and enables compatibility with forced continuous conduction mode operations

Inventive Principle:

Principle #13The other way round (Inversion)

Data Source

PatentUS12062984B2Method of operating a converter circuit, corresponding converter circuit and driver device

Publication Date: 2024.08.13 STMICROELECTRONICS SRL

AI summary

A first node of converter circuit receives an input, provides an output at a second node, and has a third node coupled by an inductance to ground. A first switch has a current path between the first and third nodes and a second switch has a current path between the third and second nodes. The converter circuit operates in a first state (with the first switch conductive and the second switch non-conductive) and a second state (with the first switch non-conductive and the second switch conductive). Current flowing through the first switch is sensed during the first state to produce a sensing signal indicative of inductance current. The sensing signal is averaged to produce an averaged sensing signal indicative of an average value of the current. The averaged sensing signal is then weighted by a time during which the second switch is conductive to produce a weighted signal.