Current Sense Circuit With Capacitive Blanking Compensation
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Solution Overview
Problem
Current current sensing in DC-DC converters experiences significant errors due to the blanking interval, especially in high-frequency and high-duty cycle applications, leading to inaccuracies in load current measurement, with errors exceeding 10% in some cases.
Innovation Solution
The implementation of a current sense circuit that includes a compensation capacitor to store sense voltage during the blanking interval and provide a compensation current during the averaging interval, reducing the error caused by the blanking interval through the addition of a compensation voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a blanking interval is used in current sensing to allow signal settling, then signal stability is improved, but measurement precision deteriorates due to loss of current data during the blanking period
Solution Approach 1:
The compensation capacitor stores the sense voltage during the blanking interval before the averaging interval begins. This preliminary action preserves the voltage information that would otherwise be lost, allowing the capacitor to discharge and compensate for the missing current data during the averaging period, thereby maintaining measurement precision while keeping the blanking interval for signal stability
Solution Approach 2:
The compensation capacitor acts as an intermediary element between the sense amplifier output and the averaging filter. It temporarily holds the sense voltage during the blanking interval and provides a compensation current during the averaging interval, mediating the transition between these two intervals and enabling accurate current measurement despite the blanking period
2Productivity
If the switching frequency is increased to improve productivity, then output power is improved, but measurement precision deteriorates due to reduced averaging time and increased blanking interval impact
Solution Approach 1:
By storing the sense voltage in the compensation capacitor during the blanking interval, the system prepares compensation data in advance. This allows the averaging filter to use this stored voltage information during the shortened averaging interval at higher switching frequencies, maintaining measurement precision even when the averaging window becomes smaller due to increased productivity requirements
Solution Approach 2:
The compensation capacitor changes the temporal distribution of voltage information. Instead of requiring a longer averaging interval for accurate measurement, the capacitor provides a compensation current that effectively extends the measurement window, allowing high switching frequencies (high productivity) to coexist with high measurement precision
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This solution significantly improves current sensing accuracy, reducing errors to less than 1% in DC-DC converters, ensuring precise load current measurement across various applications.
Implementation Method 1
The compensation capacitor is coupled to the second terminal of the switch. The capacitor is configured to store the sense voltage in a blanking interval that precedes the averaging interval, and provide a compensation current in the averaging interval
Data Source
AI summary
A current sense circuit includes a sense amplifier, a current mirror circuit, a resistor, a low-pass filter, and a capacitor. The sense amplifier is adapted to be coupled to a switching transistor of a DC-DC converter. The current mirror circuit is coupled to the sense amplifier, and is configured to generate a sense current proportional to a current flowing through the switching transistor. The resistor is coupled to the current mirror circuit, and is configured to generate a sense voltage based on the sense current. The low-pass filter is coupled to the resistor, and is configured to average the sense voltage over an averaging interval. The capacitor is coupled to the resistor, and is configured to store the sense voltage in a blanking interval that precedes the averaging interval, and provide a compensation current in the averaging interval.