APX823

Green APX823/APX824/APX825A PROCESSOR SUPERVISORY CIRCUITS Description The APX823/APX824/APX825A family of supervisors provides circuit initialization and timing supervision, primarily for DSP and processorbased systems. During power-on, RESET is asserted when supply voltage VCC becomes higher than 1.1V. Thereafter, the supply voltage supervisor monitors VCC and keeps RESET active as long as VCC remains below the threshold voltage VTH-. An internal timer delays the return of the output to the inactive state (high) to ensure proper system reset. The delay time, td starts after VCC has risen above the threshold voltage VTH-. When the supply voltage drops below the threshold voltage VTH-, the output becomes active (low) again. No external components are required. All the devices of this family have a fixed-sense threshold voltage VTH- set by an internal voltage divider. The APX823/APX825A devices incorporate a manual reset input, MR . A low level at MR causes RESET to become active. The APX824/APX825A devices include a high-level output RESET. APX823/APX824/APX825A have a watchdog timer that is periodically triggered by a positive or negative transition at WDI. When the supervising system fails to retrigger the watchdog circuit within the time-out interval, ttout, RESET becomes active for the time period td. This event also reinitializes the watchdog timer. Leaving WDI unconnected disables the watchdog. In applications where the input to the WDI pin may be active (transitioni...