Datasheet

M48T08, M48T08Y, M48T18 Operation modes
Doc ID 2411 Rev 11 13/31
2.3 Data retention mode
With valid V
CC
applied, the M48T08/18/08Y operates as a conventional BYTEWIDE™ static
RAM. Should the supply voltage decay, the RAM will automatically power-fail deselect, write
protecting itself when V
CC
falls within the V
PFD
(max), V
PFD
(min) window. All 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
PFD
(min), the
user can be assured the memory will be in a write protected state, provided the V
CC
fall time
is not less than t
F
. The M48T08/18/08Y may respond to transient noise spikes on V
CC
that
reach into the deselect window during the time the device is sampling V
CC
. Therefore,
decoupling of the power supply lines is recommended.
When V
CC
drops below V
SO
, the control circuit switches power to the internal battery which
preserves data and powers the clock. The internal button cell will maintain data in the
M48T08/18/08Y for an accumulated period of at least 10 years when V
CC
is less than V
SO
.
Note: Requires use of M4T32-BR12SH SNAPHAT
®
top when using the SOH28 package.
As system power returns and V
CC
rises above V
SO
, the battery is disconnected and the
power supply is switched to external V
CC
.
Write protection continues until V
CC
reaches V
PFD
(min) plus t
rec
(min). E1 should be kept
high or E2 low as V
CC
rises past V
PFD
(min) to prevent inadvertent WRITE cycles prior to
system stabilization. Normal RAM operation can resume t
rec
after V
CC
exceeds V
PFD
(max).
For more information on battery storage life refer to the application note AN1012.
2.4 Power-fail interrupt pin
The M48T08/18/08Y continuously monitors V
CC
. When V
CC
falls to the power-fail detect trip
point, an interrupt is immediately generated. An internal clock provides a delay of between
10 µs and 40 µs before automatically deselecting the M48T08/18/08Y. 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.