DS1747 Maxim, DS1747 Datasheet - Page 7

• Manufacturer Part Number: DS1747
• Description: The DS1747 is a full-function, year-2000-compliant (Y2KC), real-time clock/calendar (RTC) and 512k x 8 nonvolatile static RAM
• Manufacturer: Maxim

DATA-RETENTION MODE
The 5V device is fully accessible and data can be written or read only when V
However, when V
internal clock registers and SRAM are blocked from any access. At this time the power fail reset output
signal (RST) is driven active and will remain active until V
below the battery switch point V
the backup battery. RTC operation and SRAM data are maintained from the battery until V
to nominal levels. The 3.3V device is fully accessible and data can be written or read only when V
greater than V
this time the power fail reset output signal (RST) is driven active and will remain active until V
to nominal levels. If V
(V
the backup supply (V
from the battery until V
requires a pull up. Except for the RST, all control, data, and address signals must be powered down
when V
BATTERY LONGEVITY
The DS1747 has a lithium power source that is designed to provide energy for clock activity, and clock
and RAM data retention when the V
is sufficient to power the DS1747 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 V
disconnected, guaranteeing full energy capacity. When V
lithium energy source is enabled for battery backup operation. Actual life expectancy of the DS1747 will
be much longer than 10 years since no lithium battery energy is consumed when V
BATTERY MONITOR
The DS1747 constantly monitors the battery voltage of the internal battery. The Battery Flag bit (bit 7)
of the day register is used to indicate the voltage level range of the battery. This bit is not writable and
should always be a one when read. If a zero is ever present, an exhausted lithium energy source is
indicated and both the contents of the RTC and RAM are questionable.
BAT
) when V
CC
is powered down.
PF
CC
.
drops below V
When V
CC
CC
is below the power failing point, V
BAT
PF
power. Each DS1747 is shipped from Maxim with its lithium energy source
CC
) when V
is less than V
CC
is returned to nominal levels. The RST signal is an open drain output and
falls below the power fail point, V
PF
SO
.
CC
If V
(battery supply level), device power is switched from the V
CC
drops below V
supply is not present. The capability of this internal power supply
SO
PF
, the device power is switched from V
is greater than Vso
7 of 16
SO
.
RTC operation and SRAM data are maintained
PF
CC
, (point at which write protection occurs) the
is first applied at a level greater than V
CC
,
the device power is switched from V
returns to nominal levels. When V
PF
, access to the device is inhibited. At
CC
CC
CC
to the backup supply
is present.
is greater than V
CC
is returned
CC
CC
CC
returns
PF
pin to
CC
CC
falls
, the
PF
to
is
.