Dallas Semiconductor announced the DS1814 and DS1819 5-Volt and 3.3-Volt MicroMonitors, the most energy-efficient, full-function CPU supervisors available. Packaged in a space-saving SOT-23-5, the DS1814 and DS1819 utilize a new design for the bandgap reference that cuts current consumption by approximately one-fourth, compared with standard bandgap products.

CPU supervisors automatically stop, start, or hold up the CPU in response to power changes, external overrides and software execution status. Jerry Miller, product manager, said, "Since its main function is to add reliable, consistent operation, a CPU supervisor should consume as little space and power as possible. Low power use is critical in battery-powered and portable devices, both to prolong battery life and to reduce size and weight requirements. These devices consume only 15ưA quiescent current. In the SOT-23-5 package, the DS1814 and DS1819 yield maximum supervisory function for minimum size and minimum power use."

The DS1814 accurately monitors a 5-volt supply with options for 5% or 10% tolerances, while the DS1819 accurately monitors a 3.3-volt supply with options for 5%, 10% or 20% tolerances. Both utilize a precision temperature-compensated reference, comparator, oscillator, and clock chain. When power input falls below a programmed tolerance, the reset output activates and remains active for at least 140 ms after the voltage returns to an in-tolerance condition. This gives the system and power supply a chance to stabilize providing consistent, reliable system operation.

The DS1814 and DS1819 are available in three versions compatible with Maxim's MAX823/4/5, allowing for drop-in replacements to reduce system current consumption. Each device provides an active low power-on reset and two of the following three functions: active high reset output, pushbutton reset, or watchdog. The pushbutton reset control also supplies a minimum 140-ms reset pulse width before full operations resume. The watchdog timer function, which can be optionally disabled, issues a reset in the event no activity is seen on the strobe input within 1.12 seconds.

It is not usual to see a second-source part as Product of the Week, but in this case the power savings for this function are terribly important to the user. Because the CPU supervisor is effectively contributing nothing to the CPU's operation -- it doesn't make things go faster and it doesn't increase capacity -- system designers would rather it took none of the system power either. Given reality they at least want that power to be the lowest possible. In many of the applications where these parts would be used (with little or no PC use, I would expect, because of additional systems needs) a small savings of power will encourage a change in vendor choice almost on a nod. The savings here are not insubstantial and I think a large number of sockets presently occupied by Maxim parts will come across to the Dallas solutions. That scenario could of course be rather time-limited, depending on what other manufacturers are working on.