Half-Bridge Current Sensing via Low-Side Estimation
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Solution Overview
Problem
Existing current sensing methods for inductive loads in half-bridge configurations, such as buck converters, face challenges in accuracy, particularly for high-side current measurement, and introduce power dissipation due to the use of shunt resistors, with reliability issues at short duty cycles.
Innovation Solution
A current sensing circuit that estimates high-side current based on low-side current measurements during the low-side transistor conduction time, using a current sensing amplifier, output voltage estimator, and inductance estimator to calculate high-side current without shunt resistance, incorporating auto-calibration for improved accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If shunt resistors are used for current measurement, then current sensing is achieved, but power dissipation increases
Solution Approach 1:
The patent extracts the current sensing function from the main power path by using the existing low-side switch as a sensing element. Instead of inserting shunt resistors into the high-side current path, the invention utilizes the low-side switch's on-resistance during its conduction period to sense the inductor current, thereby eliminating the need for additional power-dissipating sensing resistors in the high-side path.
Solution Approach 2:
The patent introduces an intermediary approach by using the low-side switch as a mediator to sense the high-side current. The current flowing through the low-side switch during its conduction period serves as an intermediary measurement that allows indirect determination of the high-side current without directly placing sensing elements in the high-side path, thus reducing power dissipation.
2Measurement precision
If high-side current measurement is implemented directly, then accurate sensing is achieved, but device complexity increases
Solution Approach 1:
The patent applies multi-functionality by making the low-side switch serve dual purposes: power switching and current sensing. The same low-side switch that controls power flow also provides the sensing function during its conduction period, eliminating the need for separate high-side sensing circuitry and reducing overall device complexity while maintaining measurement capability.
Solution Approach 2:
Instead of directly measuring high-side current through the high-side switch, the patent inverts the approach by measuring the low-side current during the low-side switch conduction period and using that measurement to infer the high-side current. This indirect measurement approach simplifies the circuit architecture while achieving the desired sensing accuracy.
3Productivity
If short duty cycles are used, then switching frequency increases, but measurement reliability decreases
Solution Approach 1:
The patent ensures reliable measurement by performing the current sensing action during the low-side switch conduction period, which is deliberately timed to occur after the high-side switch turns off. This preliminary action of sensing during the known conduction window ensures that sufficient time is available for accurate measurement even at short duty cycles, maintaining reliability across varying switching conditions.
Data Source
AI summary
A high-side switch has a current flow path between a high-side reference and a switching node, and a low-side switch has a current flow path between the switching node and a low-side reference. The high-side switch is conductive during a first time interval and the low-side switch is conductive during a second time interval. An inductive element is coupled between the switching node and an output node. A switching voltage is sensed and filtered to provide a filtered voltage indicative of an output voltage at the output node. Based on a difference between the filtered voltage and the sensed switching voltage, an output current signal is generated that is indicative of an intensity of a current flowing through the inductive load during an estimation time equal to or greater than the first time interval.