CAN Transceiver Output Stage Regulation for Differential Signal Stability
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Solution Overview
Problem
CAN transceivers are susceptible to abnormal high-voltage interference, leading to errors in output signals due to reverse recovery currents in diodes and field effect transistors, affecting the stability of differential signals in complex electromagnetic environments.
Innovation Solution
The CAN transceiver incorporates regulation circuits that sample terminal voltages to detect abnormal high-voltage pulses, generating regulation signals to adjust the forward currents of switching transistors, ensuring stable differential signals by compensating for reverse recovery currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If protection diode is used in output stage circuit to protect against high-voltage interference, then reliability is improved, but reverse recovery current is generated during switching from forward conduction to reverse cutoff, causing output state to change from dominant to recessive and worsening signal stability
Solution Approach 1:
The patent detects abnormal high-voltage conditions in advance before they cause harmful effects. The detection circuit monitors the potential difference between high-side and low-side bus ports, and when abnormal voltage is detected, the control circuit preemptively adjusts the conduction states of switching transistors to prevent reverse recovery current from causing output state changes, thus maintaining signal stability while keeping protection diodes in place
Solution Approach 2:
The patent converts the harmful reverse recovery current effect into a beneficial protection mechanism. By detecting abnormal high-voltage conditions and using the control circuit to adjust switching transistor states, the system uses the detected abnormal voltage signal to trigger protective action that prevents the harmful effect, effectively turning the detection of harmful conditions into the mechanism for preventing harm
2Object-affected harmful factors
If regulation circuits are added to detect and regulate abnormal voltages, then electromagnetic compatibility is improved, but device complexity increases
Solution Approach 1:
The patent merges the detection and regulation functions into the existing output stage circuit structure. The detection circuit uses the existing high-side and low-side bus ports and switching transistors, adding minimal components. The control circuit integrates the detection and control functions in a unified structure that works with the existing protection diodes and switching transistors, avoiding the need for completely separate detection and regulation systems
Solution Approach 2:
The switching transistors in the output stage circuit serve multiple functions: they perform the primary data transmission function while also serving as detection elements for abnormal high-voltage conditions and as regulation elements for controlling current flow during protection events. This multi-functionality reduces the need for separate dedicated detection and regulation components, thereby limiting the increase in device complexity
Data Source
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AI summary
A CAN transceiver including a data transmission port, a high-side bus port, a low-side bus port, an output stage circuit, a first regulation circuit and a second regulation circuit. The first regulation circuit and the second regulation circuit eliminate errors of differential signals by receiving abnormal voltage signals and outputting regulation signals to increase a pull-up current or a pull-down current in the output circuit, the first regulation circuit regulates errors generated by abnormal positive high-voltage pulses coupled into the high-side bus port, and the second regulation circuit regulates errors generated by abnormal negative high-voltage pulses coupled into the low-side bus port; after the CAN transceiver applies the first regulation circuit and the second regulation circuit, influence of abnormal high-voltage pulse signals in a CAN bus on errors of output signals of the CAN transceiver is reduced, and EMC performance of the CAN transceiver is improved.