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The EM6151 offers a high level of integration by combining voltage monitoring and software monitoring using a windowed watchdog. A comparator monitors the voltage applied at the VIN input comparing it with an internal voltage reference VREF. The power-on reset function is initialized after VIN reaches VREF and takes the reset output inactive after a delay TPOR depending on external resistance ROSC. The reset output goes active low when the VIN voltage is less than VREF. The RESET and EN outputs are guaranteed to be in a correct state for a regulated output voltage as low as 1.2 V. The watchdog function monitors software cycle time and execution. If software clears the watchdog too quickly (incorrect cycle time) or too slowly (incorrect execution) it will cause the system to be reset. The system enable output prevents critical control functions being activated until software has successfully cleared the watchdog three times. Such a security could be used to prevent motor controls being energized on repeated resets of a faulty system. When the microcontroller goes in stand-by mode or stops working, no signal is received on the TCL input of the EM6151 (version 55) and it goes into a stand-by mode in order to save power (CAN-bus sleep detector).
ToolsResistor Calculation Tool
The excel file below helps to calculate the value of the external resistor ROSC for a given/wanted watchdog timeout period.