DS1553 datasheet(5/20 Pages) MAXIM

5 / 20 page

DS1553 64kB, Nonvolatile, Year-2000-Compliant Timekeeping RAM

5 of 20

below VSO. RTC operation and SRAM data are maintained from the battery until VCC is returned to

nominal levels.

All control, data, and address signals must be powered down when VCC is powered down.

BATTERY LONGEVITY

The DS1553 has a lithium power source that is designed to provide energy for the clock activity and

clock and RAM data retention when the VCC supply is not present. The capability of this internal power

supply is sufficient to power the DS1553 continuously for the life of the equipment in which it is

installed. For specification purposes, the life expectancy is 10 years at +25

C with the internal clock

oscillator running in the absence of VCC. Each DS1553 is shipped from Dallas Semiconductor with its

lithium energy source disconnected, guaranteeing full energy capacity. When VCC is first applied at a

level greater than VPF, the lithium energy source is enabled for battery backup operation.

INTERNAL BATTERY MONITOR

The DS1553 constantly monitors the battery voltage of the internal battery. The Battery Low Flag (BLF)

bit of the Flags register (B4 of 1FF0h) is not writeable and should always be 0 when read. If a 1 is ever

present, an exhausted lithium energy source is indicated, and both the contents of the RTC and RAM are

questionable.

POWER-ON RESET

A temperature-compensated comparator circuit monitors the VCC level. When VCC falls to the power-fail

trip point, the RST signal (open drain) is pulled low. When VCC returns to nominal levels, the RST signal

continues to be pulled low for 40ms to 200ms. The power-on reset function is independent of the RTC

oscillator and is therefore operational whether or not the oscillator is enabled.

DS1553 Datasheet(PDF) 5 Page - Maxim Integrated Products