Rainbow Electronics DS1258Y_AB - Manual (Page 3)

DS1258Y/AB
100395 3/9
DATA RETENTION MODE
The DS1258AB provides full functional capability for
V
CC
greater than 4.75 volts, and write protects by 4.5
volts. The DS1258Y provides full functional capability
for V
CC
greater than 4.5 volts and write protects by 4.25
volts. Data is maintained in the absence of V
CC
without
any additional support circuitry. The nonvolatile static
RAMs constantly monitor V
CC
. Should the supply volt-
age decay, the NV SRAMs automatically write protect
themselves, all inputs become “don’t care,” and all out-
puts become high impedance. As V
CC
falls below ap-
proximately 3.0 volts, a power switching circuit con-
nects the lithium energy source to RAM to retain data.
During power-up, when V
CC
rises above approximately
3.0 volts, the power switching circuit connects external
V
CC
to RAM and disconnects the lithium energy source.
Normal RAM operation can resume after V
CC
exceeds
4.75 volts for the DS1258AB and 4.5 volts for the
DS1258Y.
FRESHNESS SEAL
The DS1258 devices are shipped from Dallas Semicon-
ductor with the lithium energy sources disconnected,
guaranteeing full energy capacity. When V
CC
is first
applied at a level greater than V
TP
, the lithium energy
source is enabled for battery backup operation.