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ST offers eight new supervisor circuits with short lead times

Posted: 20 Oct 2005 ?? ?Print Version ?Bookmark and Share

Keywords:stmicroelectronics? st? microprocessor supervisor circuit? stm6717? stm6718?

Dual/triple microprocessor supervisor circuits

STMicroelectronics (ST) introduced a family of dual/triple microprocessor supervisor circuits that offers a wide range of voltage combinations, a compact 5/6-pin SOT23 package, and a new manufacturing flow that ensures short lead times. In addition, several devices in the family incorporate a Manual Reset Delay function, which helps protect equipment such as STBs against inadvertent resets.

Aside from STBs, the new STM6717/18/19/20 and STM6777/78/79/80 supervisors are aimed at portable battery-powered systems, networking and communication systems, where the processor core (microprocessor, DSP or ASIC) typically requires a 1.8V or lower voltage supply and the on-chip peripherals typically require a 3V or 3.3V supply. Such systems typically need to simultaneously monitor at least two power rails and many require monitoring an additional third rail, explained the company.

The STM67xx family initially comprises eight generic devices, all of which monitor the system supply (VCC1) against a fixed threshold value and provide an active-low reset output when they detect an out-of-tolerance condition. These products integrate a reset function that is guaranteed to be asserted for VCC down to 0.8V, with a minimum duration of 140ms. Four of the devices have open drain outputs while the other four have push-pull outputs. Six of the eight devices (STM6717/18/19/20 and STM6777/78) also monitor a second supply input (VCC2) against a second, fixed threshold value and generate a reset if either of the two monitored VCC rails goes out of tolerance. The threshold voltages for these two monitored rails are factory-set and customer-selectable. Currently, ST offers some 23 combinations of VCC1 and VCC2 thresholds, with many more possible. Reset thresholds for VCC1 range from 4.625V down to 1.575V (nominal), while thresholds for VCC2 range from 3.075V down to 0.788V (nominal), allowing the customer to select all popular combinations of power supply rails.

Additionally, the STM6719/20 and STM6779/80 include an adjustable input which is compared to a 0.625V internal reference. Using an external resistor divider, these devices can monitor an additional supply rail and they will generate a reset signal if any of the fixed or adjustable rails goes out of tolerance. With two fixed inputs and one adjustable one, the STM6719/20 can monitor three supply rails.

All eight devices include an active-low Manual Reset input for push-button reset use. The STM6717/18/19/20 family provides drop-in replacements for the MAX6717/18/19/20 supervisors but offer lower power consumption; the supply current for the STM67xx devices is typically 11?A, compared with 14?A for the competitive products at the same supply voltage.

Another benefit of the new family is that all the devices are manufactured using a production flow that ensures short lead times through the optimized use of laser trimming to customize the devices at a late stage in the fabrication process. After a full electrical test of the generic dice, laser trimming is used both to blow fusible links that convert the generic device into the specific part and to trim the analog circuitry, ST explained. After the laser stage, a final test is performed on the specific device. This production flow allows a large number of different devices to be obtained from a single mask set in a cost-effective and flexible manner, added the company.

All of the new STM67xx devices are available for production, with prices starting at 40 cents in volume orders.

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