Low-Ohmic Circuit Path for Daisy-Chain Communication Continuity
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Solution Overview
Problem
In daisy-chain circuits used in safety-relevant applications, communication is interrupted when a slave device is not powered, as the output driver of the unpowered slave device can drive an undefined voltage, and the input driver cannot detect an input voltage, leading to disruptions in data exchange.
Innovation Solution
The implementation of a low-ohmic circuit path and an under-voltage lockout (UVLO) circuit that selects between a normal operation circuit path and a low-ohmic circuit path based on the supply voltage, allowing the daisy-chain circuit to continue operation even when a slave device is not powered, by forcing the input pin to a defined voltage and using a bidirectional normally-on switch to ensure transparent pin mode.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a daisy-chain circuit is used with conventional slave devices, then the circuit structure is simple and easy to implement, but communication is interrupted when a slave device is not powered
Solution Approach 1:
The slave device changes its output impedance parameter based on power status. When powered, the output driver has high impedance in normal operation. When under-voltage or unpowered, the UVLO circuit activates to create a low-impedance path that forces the output pin to a defined voltage level, allowing the device to be detected as present while preventing communication disruption
Solution Approach 2:
The UVLO circuit acts as an intermediary between the power supply and the output driver. It monitors the supply voltage and intervenes by activating the low-impedance path when voltage is insufficient, thereby mediating between the powered/unpowered state and the communication bus to ensure continuous operation
2Reliability
If pull-up or pull-down devices are added to ensure safe input levels, then input voltage detection is improved, but the device complexity increases
Solution Approach 1:
The patent merges the function of pull-down devices into the slave device's own output stage. Instead of adding separate pull-down resistors to each slave device, the output driver and UVLO circuit are designed to inherently provide the pull-down function when needed, eliminating the need for additional discrete components
Solution Approach 2:
The slave device serves itself by using its own output driver and UVLO circuit to provide the necessary voltage level definition. The device monitors its own power status and automatically activates the low-impedance path to force its output pin to a defined level, eliminating the need for external pull-up or pull-down devices
Data Source
AI summary
A device, including a low-ohmic circuit path; a normal operation circuit path coupled in parallel with the low-ohmic circuit path; and a circuit element configured to select between the low-ohmic circuit path and the normal operation circuit path.