Microprocessor Supervisory Circuit With Watchdog Timer & Manual Reset

The TS823 TS824/TS825 family allows the user to customize the CPU monitoring function without any external components. The user has a large choice of reset voltage thresholds and output driver configurations, all of which are present ant the factory. Each wafer is trimmed to the customer specifications. These circuits will ignore fast negative going transients on Vdd. The state of the reset output is guaranteed to be correct down to 1V. After Vdd crosses above a factory present threshold, the TS823 TS824/TS825 assert a reset signal. After a predetermined time (the eset,interval) the reset is deasserted. If Vdd ever drops below the threshold voltage a reset is asserted immediately. In addition to a supply monitoring function the TS823 TS824/TS825 also monitor transitions at the watchdog (WDI) input. If a Logic transition does not occur at the WDI pin within a certain time interval (the atchdog,interval) then a reset is asserted. The reset deasserts after the reset interval, as explained earlier. The TS823 TS824/TS825 CAN both assert a reset manually by pulling the MR input to ground, and the micro-power quiescent current make this family a natural for portable battery powered equipment. By Taiwan Semiconductor Company, Ltd. (TSC)