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Supervisory IC with watchdog timer

Posted: 09 Sep 2005 ?? ?Print Version ?Bookmark and Share

Keywords:em nicroelectronic? swatch group? em6151? microprocessor voltage supervisory ic?

With programmable reset threshold voltages

EM Microelectronic, an electronic systems company of the Swatch Group, unveiled 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, the EM6151 circuit is available in several versions, allowing for different ratios of the opened/closed window of the watchdog and power saving function compatible with CAN-bus sleep mode. The EM6151 features an open drain reset output, comes in a compact 8-pin SO8 package, operates over the -40C to 125C temperature range, and draws 35?A quiescent current.

The EM6151 features an increased confidence ENABLE output, which can be used to drive critical control functions or to gate motor signals. This signal is only asserted after the software has successfully cleared the watchdog three times.

According to EM Micro, the 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.

The EM6151 features a time-windowed watchdog function that is said to recognize 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, said the company. In contrast, the EM6151 windowed watchdog ensures that the timer clear signal occurs within the correct time window ("opened" window); otherwise it activates a system reset or other error handling.

In addition, timings of the watchdog function in the EM6151 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, as well as the reset threshold voltage using an external two-resistor voltage divider.

Version 53 comes with a large opened watchdog window (67 percent), making it easier for the software programmer to issue a pulse to service the watchdog; Version 50 has a smaller opened watchdog window (33 percent), offering increased security in the application; and Version 55 offers a Controller Area Network bus (CAN-bus) sleep mode detector.

The EM6152 has the same functions as EM6151 but features a 5V automotive voltage regulator, guaranteeing 400mA in output. The EM6151 is available in an SO8 package.

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