M48T08 ST Microelectronics, M48T08 Datasheet - Page 10

• Manufacturer Part Number: M48T08
• Description: 64 Kbit 8Kb x 8 TIMEKEEPER SRAM
• Manufacturer: ST Microelectronics

M48T08, M48T18
DATA RETENTION MODE
With valid V
a conventional BYTEWIDE static RAM. Should the
supply voltage decay, the RAM will automatically
power-fail deselect, write protecting itself when V
falls within the V
outputs become high impedance, and all inputs are
treated as "don’t care."
Note: A power failure during a write cycle may
corrupt data at the currently addressed location,
but does not jeopardize the rest of the RAM’s
content. At voltages below V
be assured the memory will be in a write protected
state, provided the V
The M48T08/18 may respond to transient noise
spikes on V
during the time the device is sampling V
fore, decoupling of the power supply lines is rec-
ommended.
When V
switches power to the internal battery which pre-
serves data and powers the clock. The internal
button cell will maintain data in the M48T08/18 for
an accumulated period of at least 10 years when
V
V
and the power supply is switched to external V
Figure 9. Predicted Battery Storage Life versus Temperature
10/19
CC
CC
is less than V
rises above V
CC
CC
CC
50
40
30
20
10
drops below V
8
6
5
4
3
2
1
20
applied, the M48T08/18 operates as
that reach into the deselect window
PFD
SO
SO
. As system power returns and
(max), V
CC
, the battery is disconnected,
fall time is not less than t
30
SO
PFD
PFD
, the control circuit
(min), the user can
(min) window. All
40
CC
. There-
TEMPERATURE (Degrees Celsius)
CC
CC
F
50
.
.
Write protection continues until V
(min) plus t
low as V
tent write cycles prior to system stabilization. Nor-
mal RAM operation can resume t
exceeds V
For more information on Battery Storage Life refer
to the Applicatio Noyte ANxxx.
POWER FAIL INTERRUPT PIN
The M48T08/18 continuously monitors V
V
interrupt is immediately generated. An internal
clock provides a delay of between 10 s and 40 s
before automatically deselecting the M48T08/18.
The INT pin is an open drain output and requires
an external pull up resistor, even if the interrupt
output function is not being used.
SYSTEM BATTERY LIFE
The useful life of the battery in the M48T08/18 is
expected to ultimately come to an end for one of
two reasons: either because it has been dis-
charged while providing current to the RAM and
clock in the battery back-up mode, or because the
effects of aging render the cell useless before it can
CC
falls to the power-fail detect trip point, an
60
t1%
CC
PFD
REC
rises past V
(max).
(min). E1 should be kept high or E2
70
t50% (AVERAGE)
PFD
(min) to prevent inadver-
80
CC
REC
reaches V
AI01024
after V
CC
90
. When
PFD
CC