How to detect open/short circuit failures

・In Japanese
＜Premise knowledge＞
・pull-up/pull-down resistor

■How to detect open/short circuit failures

This section describes how to detect when the sensor input to the control unit has an open/short failure. As a general circuit, it is assumed that the sensor and pull-up/pull-down resistors are attached as shown below.

Case① With pull-down resistor
Failure modes include disconnection, ground short, and power supply short. When a failure occurs, the voltage level seen from the CPU sticks to 5V or 0V, so that failure is detected.



Case② With pull-down resistor
The concept is the same as for pull-downs, and failures are detected at the voltage levels of disconnection, ground short, and power supply short. As shown in the figure below, if the internal circuit is shorted, it cannot be distinguished from the sensor disconnection, but since the failure rate of internal circuit failure is lower than the sensor disconnection, it is better to suspect the sensor disconnection first.

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