
M48T08, M48T18, M48T08Y
14/26
Data Retention Mode
With valid VCC applied, the M48T08/18/08Y oper-
ates as a conventional BYTEWIDE static RAM.
Should the supply voltage decay, the RAM will au-
tomatically power-fail deselect, write protecting it-
self when VCC falls within the VPFD (max), VPFD
(min) window. All outputs become high imped-
ance, 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 con-
tent. At voltages below VPFD (min), the user can be
assured the memory will be in a write protected
state, provided the VCC fall time is not less than tF.
The M48T08/18/08Y may respond to transient
noise spikes on VCC that reach into the deselect
window during the time the device is sampling
VCC. Therefore, decoupling of the power supply
lines is recommended.
When VCC drops below VSO, the control circuit
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/
08Y for an accumulated period of at least 10 years
when VCC is less than VSO.
Note:
Requires
use
of
M4T32-BR12SH
SNAPHAT top when using the SOH28 package.
As system power returns and VCC rises above
VSO, the battery is disconnected and the power
supply is switched to external VCC.
Write protection continues until VCC reaches VPFD
(min) plus tREC (min). E1 should be kept high or E2
low as VCC rises past VPFD (min) to prevent inad-
vertent WRITE cycles prior to system stabilization.
Normal RAM operation can resume tREC after VCC
exceeds VPFD (max).
For more information on Battery Storage Life refer
to the Application Note AN1012.
Power-fail Interrupt Pin
The M48T08/18/08Y continuously monitors VCC.
When VCC falls to the power-fail detect trip point,
an interrupt is immediately generated. An internal
clock provides a delay of between 10s and 40s
before automatically deselecting the M48T08/18/
08Y. The INT pin is an open drain output and re-
quires an external pull up resistor, even if the inter-
rupt output function is not being used.
Figure 11. Power Down/Up Mode AC Waveforms
Note: Inputs may or may not be recognized at this time. Caution should be taken to keep E1 high or E2 low as VCC rises past VPFD (min).
Some systems may perform inadvertent WRITE cycles after VCC rises above VPFD (min) but before normal system operations begin.
Even though a power on reset is being applied to the processor, a reset condition may not occur until after the system clock is running.
AI00566
VCC
INPUTS
INT
(PER CONTROL INPUT)
OUTPUTS
DON'T CARE
HIGH-Z
tF
tFB
tPFX
tR
tPFH
tREC
tPD
tRB
tDR
VALID
NOTE
(PER CONTROL INPUT)
RECOGNIZED
VPFD (max)
VPFD (min)
VSO