Low-Side Driving Circuit for Power Transistor with Noise-Immune FO Pin
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Solution Overview
Problem
The existing power conversion apparatuses face a mismatch between the internal protection state and the state of the fail (FO) pin due to external wiring issues or noise contamination, leading to incorrect abnormal state detection by the microcontroller, which can result in inappropriate protection operations.
Innovation Solution
A driving circuit with a protection circuit, alarm control circuit, judgment circuit, and control logic circuit that generates and compares protection and judgment signals to accurately reflect the internal state of the power module, ensuring proper control of the power transistor and preventing unnecessary protection operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an open-drain interface is employed for the FO pin with external wiring to the microcontroller, then the microcontroller can detect abnormal states, but wiring issues or noise contamination can cause mismatch between internal protection state and FO pin state
Solution Approach 1:
The patent introduces an intermediary judgment circuit between the internal protection circuit and the external FO pin. This judgment circuit compares the voltage at the FO pin with a reference voltage to determine the actual abnormal state, acting as a mediator that filters out noise and wiring issues while transmitting the true protection status to the microcontroller.
Solution Approach 2:
The patent implements a feedback mechanism where the judgment circuit continuously monitors the FO pin voltage and compares it with the reference voltage, then feeds back the corrected abnormal state information to the microcontroller. This feedback loop ensures that the microcontroller receives accurate protection status information despite external interference.
2Device complexity
If the FO pin voltage is directly used for abnormal state judgment, then the circuit is simple, but external noise or short-circuit can cause incorrect detection
Solution Approach 1:
The judgment circuit serves as an intermediary layer between the simple FO pin voltage signal and the final abnormal state determination. It introduces a reference voltage comparison mechanism that maintains relatively simple circuitry while significantly improving detection accuracy by filtering out noise and false signals.
3Speed
If no voltage comparison mechanism is used, then the response is fast, but mismatch between internal state and FO pin state leads to incorrect protection operations
Solution Approach 1:
The judgment circuit performs preliminary action by comparing the FO pin voltage with the reference voltage before the microcontroller makes the final protection decision. This preliminary comparison ensures that the subsequent protection operation is based on accurate state information, preventing incorrect operations while maintaining fast response through the direct voltage comparison mechanism.
Data Source
AI summary
A low-side driving circuit forms a power conversion apparatus together with a power transistor to be driven. A protection circuit generates a protection signal S1. An alarm control circuit changes an electrical state of a fail terminal according to the protection signal S1. A judgment circuit compares a voltage VFO at a fail (FO) terminal with a predetermined threshold value, and generates a judgment signal S2 that indicates the comparison result. A control logic circuit controls the state of the power transistor based on the judgment signal S2 and the protection signal S1.