Two new families of microprocessor supervisory circuits from Texas Instruments (TI) feature the industry's first 2.5 volt supervisory circuit in a SOT-23 package. The devices combine a reset output, watchdog timer and manual reset all in an ultra small package. This coupled with low power consumption make the supervisory circuits ideal for digital signal processor (DSP) and portable battery-powered applications. Examples include laptop computers, personal digital assistants (PDAs), wireless telephones, computer games and portable test systems.

The two families, designated the TPS3823-XX and TPS3824-XX, monitor the system's power supply and processor timing. In the event of a power loss or faulty processor operation, the circuit generates a reset signal to the processor. Both product families require no external capacitors or resistors which saves both board space and system cost - crucial considerations in all portable applications.

"Besides broadening TI's portfolio of microprocessor supervisory circuits, we're introducing the industry's first 2.5V supervisor in a SOT-23 package -- providing a DSP solution for today's advanced mixed-voltage DSPs. A good example is TI's TMS320C549, which features a 2.5V processing core and 3.3V input/output (I/O) lines," said Bob Newton, Analog Products Specialist at TI. "The tiny five-pin small outline transistor (SOT23) surface mount package is one of the smallest packages available in the industry today. And these new devices consume only 25 micro-amps, which extends the battery life in portable applications."

Both the TPS3823-XX and the TPS3824-XX families are made up of four devices with different voltage ratings of 2.5V, 3.0V, 3.3V and 5.0V. The TPS3823 devices feature a manual reset capability, while the TPS3824 devices have the flexibility of generating a reset with either a high voltage or a low voltage signal, depending on the needs of the processor. During system power up, the Reset output becomes active at 1.1 V. Reset threshold voltages are accurate to 2 percent.

Although clearly designed as direct support for TI's own DSPs these devices will have design wins elsewhere if only because of the package. They do what you expect them to do with both high- and low-voltage resets, they are in sufficient voltage ratings, they consume minimal power and they are small. The pricing seems a little high but I doubt that the 100 k price bears any real semblance of recognition to the quoted 1000-piece price. Apart from adding to the support for their own parts these will sell extremely well to users of other manufacturers' processors.

Fabrication of these TPS3823/4 devices uses TI's LinBiCMOS process; they are in production and listed at $2.38 in 1000-piece lots.