Watchdog guards MPU supplies: News from EM Microelectronic

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New from EM Microelectronic, the EM6151 is a highly integrated microprocessor voltage supervisory IC with programmable reset threshold voltages and a watchdog timer with programmable time window and system enable output. For maximum flexibility, this circuit is available in several versions, allowing for different ratios of the opened/closed window of the watchdog and power saving function compatible with CANbus sleep mode. The EM6151 features an open drain reset output, comes in a compact 8-pin SO8 package and operates over the temperature range from -40 to +125C, making it compatible with the demanding temperature extremes in automotive and industrial environments.

A low power product, EM6151 draws only 35uA quiescent current.

EM6151 features an increased confidence enable output.

This enable output can be used to drive critical control functions or to gate motor signals; for instance, it can immediately stop the motor movement when the processor behaviour can not be trusted and only allow it again when there is confidence that the processor is running properly.

This signal is only asserted after the software has successfully cleared the watchdog three times.

This combined effect of supply voltage surveillance, watchdog timing surveillance and system enable output provides extreme reliability and security in critical microprocessor-controlled automotive, transportation, robotic and industrial control applications.

This also eliminates the need for redundant microprocessors that supervise each other.

In automotive applications, EM6151 is used to monitor the microprocessors that control electronic cockpit security and the steering column as well as other functions such as trunk closure systems, electrical spoiler control, and electrical seat, dashboard, sunroof, rear-view mirror and window controls.

Industrial applications include automated teller machines (ATMs), robotics and process control equipment.

Watchdog functions are used to ensure that system microprocessors or controllers do not operate erroneously as a result of the power supply voltage being out of specified operating range, which is especially critical during system power-up and power-down sequencing.

The EM6151 features a time-windowed watchdog function that recognises far more faults than the standard watchdogs used with microprocessors.

Standard watchdogs, whether internal to the CPU or external, are dependent on the CPU hardware and software to generate a counter reset signal and therefore will not reliably prevent hardware and software errors.

In contrast, the EM6151 windowed watchdog ensure that the timer clear signal occurs within the correct time window ('opened' window); otherwise it activates a system reset or other error handling.

This is the most robust and reliable type of watchdog action, because it effectively covers hardware errors as well as software errors such as code executing too slowly or too quickly.

Indeed, code execution may be too quick when a slave MCU conflicts with its master or when the crystal oscillator malfunctions.

Such errors and malfunctions are caught by a windowed watchdog but not by a standard watchdog, thus offering increased security.

In the EM6151, timings of the watchdog function are programmable using one external resistor to set the power-on reset delay and the watchdog time.

The ratio for the close/open watchdog window is factory programmable.

In addition, the reset threshold voltage is also programmable using an external two-resistor voltage divider.

Version 53 (V53) comes with a large opened watchdog window (67%), making it easier for the software programmer to issue a pulse to service the watchdog.

Version 50 (V50) has a smaller opened watchdog window (33%), offering increased security in the application.

Version 55 (V55) offers a Controller Area Network bus (CANbus) sleep mode detector.

In a typical automotive or industrial application, a central processor can issue a general 'sleep' instruction to all EM6151V55-equipped peripheral modules.

In sleep mode, the EM6151V55 will greatly reduce the rate that they generate reset signals.

This greatly reduces power drain when the system is off and extends battery life, which is a tremendous benefit for vehicles and equipment that is garaged or offline for periods of days or weeks at a time.

The EM6151 is a member of a family of products targeted for mission safe applications.

The EM6152 has the same functions as the EM6151 but features a 5V automotive voltage regulator guaranteeing 400mA in output.

The EM6151 windowed watchdog IC is available in SO8 packages from EM Microelectronic and its authorised distributors.

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Watchdog guards MPU supplies

The EM6151 is a highly integrated microprocessor voltage supervisory IC with programmable reset threshold voltages and a watchdog timer with programmable time window and system enable output.