The DS1321+ is a flexible non-volatile controller with lithium battery monitor in 16 pin DIP package. It is a CMOS circuit which solves application problem of converting CMOS SRAMs into non-volatile memory. Incoming power is monitored for an out of tolerance condition when such condition is detected, chip enable outputs are inhibited to accomplish write protection and battery is switched on to supply SRAMs with uninterrupted power. Special circuitry uses low leakage CMOS process which affords precise voltage detection at extremely low battery consumption. One DS1321 can support as many as four SRAMs arranged in any of three memory configurations. In addition to battery backup support, the DS1321 performs important function of monitoring remaining capacity of lithium battery and providing warning before battery reaches end of life. The device performs such measurement by periodically comparing voltage of battery as it supports an internal resistive load with selected reference voltage.
Supply voltage range from 4.75V to 5.5V (TOL=GND) and 4.5V to 5.5V ( TOL=VCCO)
Operating temperature range from -40°C to 85°C
VCC trip point of 4.62V (TOL=GND) and 4.37V (TOL=VCCO)
Operating current (TTL inputs) of 1mA and 100μA (CMOS inputs)
Automatically switches to battery backup supply when VCC power failure occurs
Monitors voltage of lithium cell and provides advanced warning of impending battery failure
Signals low battery condition on active low battery warning output signal
Resets processor when power failure occurs and holds processor in reset during system power-up
Optional 5% or 10% power fail detection
Unconditionally write protects SRAM when VCC is out of tolerance
