The EM6153 offers a high level of integration by combining voltage regulation, 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 inverted RES 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. For enhanced security, the watchdog must be serviced within an “open” time window. During the remaining time, the watchdog time window is “closed” and a reset will occur should an inverted TCL pulse be received by the watchdog during this “closed” time window. The ratio of the open/closed window is either 33%/67% or 67%/33%.
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 inverted TCL input and the EM6153 (version 55) goes into a stand-by mode in order to save power (CAN-bus sleep detector). In EM6153, the voltage regulator has a low dropout voltage and a low quiescent current of 75 /m/A. The quiescent current increases only slightly in dropout prolonging battery life. Built-in protection includes a positive transient absorber for up to 45 V (load dump) and the ability to survive an unregulated input voltage of -42 V (reverse battery). The input may be connected to ground or to a reverse voltage without reverse current flowing from the output to the input.
- Automotive systems
- Home security systems
- Telecom / Networking
- Set top boxes
Resistor Calculation Tool
The excel file below helps to calculate the value of the external resistor ROSC for a given/wanted watchdog timeout period.