X55020

This device combines power-on reset control, battery switch circuit, watchdog timer, supply voltage supervision, secondary voltage supervision, and 4Kbit serial EEPROM in one package. This combination lowers system cost, reduces board space requirements, and increases reliability. Applying power to the device activates the power onreset circuit which holds RESET/RESET active for aperiod of time. This allows the power supply and oscillatorto stabilize before the processor can execute code.A system battery switch circuit compares VCC(V1MON) with VBATTinput and connects VOUTtowhichever is higher. This provides voltage to external SRAM or other circuits in the event of main power failure. The X55020 can drive 50mA from V CC and 250A from V BATT . The device switches to V BATT when VCC drops below the low V CC voltage threshold and V BATT .

The Watchdog Timer provides an independent protection mechanism for microcontrollers. When the microcontroller fails to restart a timer within a selectable time-out interval, the device activates the RESET/ RESET signal. The user selects the interval from three preset values. Once selected, the interval does not change, even after cycling the power.    The device's low V CC detection circuitry protects the user's system from low voltage conditions, resetting the system when VCC (V1MON) falls below the minimum V CC trip point (V1 TRIP ). RESET/RESET is asserted  until V CC returns to proper operating level and stabilizes. A second voltage monitor circuit tracks the unregulated supply or monitors a second power supply voltage to provide a power fail warning. Xicor's unique circuits allow the threshold for either voltage monitor to be reprogrammed to meet special needs or to fine-tune the threshold for applications requiring higher precision.