IMP, Inc. announced two microprocessor supervisor integrated circuit families with reset functions for 3.0-, 3.3- and 4.0-volt power supply rails. Compared to pin-compatible devices available from Maxim Integrated Products, the IMP706P/R/S/T/J and IMP708R/S/T/J microprocessor supervisors feature 30-percent lower supply current and include a 4-volt supply monitoring option. Maximum supply current is a low 140 microamperes. In addition, the internal watchdog timer can be disabled, an often needed capability during system development and debugging.

Manual and automatic reset control, watchdog monitoring and a universal power-failure warning are the supervisory features that provide low-cost fault protection for digital systems without additional active components.

ýThis represents our second group of low threshold supervisors,ý said Barry Wiley, IMPýs vice president of marketing, sales and applications. ýWe enhanced the watchdog timer, reduced supply current by 30-percent and added the customer requested 4-volt threshold option.ý

IMP706 Watchdog Function Enhanced
The IMP706 watchdog timer was improved by adding a disable function. It is often desirable to disable the watchdog timer during the system development phase or in troubleshooting a system in the field.

The watchdog function monitors microprocessor responsiveness by requiring a periodic input at specific time intervals. If the watchdog input is not toggled within the 1.6-second time-out period, the watchdog output will go low to signal a fault condition. The watchdog output normally remains in the high state as long as the watchdog input is continually toggled.

Product Features and Summary Table
The IMP706 integrated circuits with watchdog timer insure that a microprocessor system starts in a known state during power-up and after a brownout condition. The IMP706R/S/T/J differ in their reset voltage levels, which are 2.63 volts, 2.93 volts, 3.08 volts and 4.00 volts respectively. All IMP706R/S/T/J devices have active low reset signals. The IMP706P reset threshold is also 2.63 volts, but the reset signal is active high.

The IMP708 has the same threshold voltage options as the IMP706 but does not have a watchdog timer. The IMP708 has both active high and active low reset signals.

All devices have a manual reset input. This input can be connected to a switch for manual reset or to host logic for program-activated reset. When connected to a switch, the 140 millisecond minimum pulse-width effectively debounces the mechanical switch.

A signaling feature is provided by a voltage monitor function. This function includes a voltage comparator, a 1.25-volt reference and associated logic, and will drive an output pin low when the monitored voltage drops below the 1.25-volt threshold. Power-supply failure, low-battery detection or general-purpose voltage monitoring can be implemented with this comparator function.

It is great to watch this company re-invent itself in the market; its decision to be a power management manufacturing company now looks like it was a good way to go although the analysts have been rather unkind -- and not necessarily logical. I sometimes wonder if Wall Street doesn't go out of its way to punish some companies, a sort of collective time-out, when it sees bottom line performances that disappoint it without trying to understand the reasons or the future opportunities.

These supervisors are good and will be adopted. I'm glad someone recognized at last that a 4.0-V market exists! The reduced power is nice and I love the manual disable for the watchdog which will allow for a great deal more work to be done in a session in debugging in many embedded applications, or during maintenance problems; I hope that it gets used. Not enough people, foolishly, will use the signaling function provided by the on-board 1.25-V reference and logic comparison. The price on these parts is also right for the current market conditions.