Overcurrent Detection Circuit Using Replica Transistor
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Solution Overview
Problem
Existing overcurrent detection circuits for DC-DC converters fail to accurately detect overcurrent due to on-resistance variations in output transistors caused by temperature or manufacturing factors, and they are inefficient in detecting multiple overcurrent levels, leading to increased power consumption and chip area usage.
Innovation Solution
An overcurrent detection circuit that includes a constant current circuit generating a reference current, a replica transistor to produce a reference voltage, and a voltage-current conversion circuit to generate a determination reference current and voltage, allowing accurate detection of overcurrent levels across multiple channels without significant power consumption or chip area expansion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a reference current generation circuit is always active to detect overcurrent irrespective of on-resistance variations, then detection accuracy is improved, but power consumption increases
Solution Approach 1:
The reference current generation circuit operates periodically based on the switching state of the output transistor rather than continuously. The circuit activates the reference current only during specific switching periods when overcurrent detection is needed, thereby maintaining detection accuracy while significantly reducing overall power consumption.
2Measurement precision
If separate reference current generation circuits are provided for each DC-DC converter channel, then overcurrent detection accuracy for each channel is improved, but chip area increases
Solution Approach 1:
A single reference current generation circuit is designed to serve multiple DC-DC converter channels. The circuit generates reference currents that can be shared across different channels through current mirrors or distribution networks, enabling accurate overcurrent detection for each channel without requiring separate dedicated circuits, thus reducing chip area while maintaining detection precision.
3Area of stationary object
If a single reference current generation circuit is used for multiple DC-DC converter channels, then chip area is reduced, but the circuit becomes more complex to manage multiple overcurrent levels
Solution Approach 1:
The reference current generation circuit is segmented into modular functional blocks that can be independently configured for different channels. Each channel's overcurrent detection threshold is set by independent resistor elements or current mirror ratios, allowing the single circuit to handle multiple overcurrent levels without excessive complexity. The segmentation enables systematic scaling to additional channels.
4Device complexity
If on-resistance variations of output transistor are not compensated, then circuit simplicity is maintained, but overcurrent detection accuracy deteriorates
Solution Approach 1:
A replica transistor is introduced that copies the on-resistance characteristics of the output transistor. The reference current generation circuit uses this replica transistor to generate a reference current that automatically compensates for on-resistance variations in the actual output transistor. This copying approach maintains relatively simple circuitry while significantly improving detection accuracy by tracking temperature and process variations.
Data Source
AI summary
A circuit for detecting overcurrent flowing to an output transistor. A replica transistor generates a reference voltage that is in accordance with a reference current flowing from a constant current circuit. A voltage-current conversion circuit generates a determination reference current proportional to the reference current based on the reference voltage. A current-voltage conversion circuit converts the determination reference current to a determination reference voltage. A detector detects overcurrent flowing to the output transistor based on the determination reference voltage.