M48Z02 ST Microelectronics, M48Z02 Datasheet - Page 9

• Manufacturer Part Number: M48Z02
• Description: 16 Kbit 2Kb x 8 ZEROPOWER SRAM
• Manufacturer: ST Microelectronics

DATA RETENTION MODE
With valid V
a conventional BYTEWIDE
the supply voltage decay, the RAM will automat-
ically power-fail deselect, write protecting itself
when V
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
be assured the memory will be in a write protected
state, provided the V
The M48Z02/12 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.
The power switching circuit connects external V
to the RAM and disconnects the battery when V
rises above V
is checked. If the voltage is too low, an internal
Battery Not OK (BOK) flag will be set. The BOK flag
can be checked after power up. If the BOK flag is
set, the first write attempted will be blocked. The
flag is automatically cleared after the first write, and
normal RAM operation resumes. Figure 9 illus-
trates how a BOK check routine could be struc-
tured.
POWER SUPPLY DECOUPLING and UNDER-
SHOOT PROTECTION
I
switching, can produce voltage fluctuations, result-
ing in spikes on the V
be reduced if capacitors are used to store energy,
which stabilizes the V
the bypass capacitors will be released as low going
spikes are generated or energy will be absorbed
when overshoots occur. A ceramic bypass capaci-
tor value of 0.1 F (as shown in Figure 10) is
recommended in order to provide the needed filter-
ing.
In addition to transients that are caused by normal
SRAM operation, power cycling can generate
negative voltage spikes on V
values below V
negative spikes can cause data corruption in the
SRAM while in battery backup mode. To protect
from these voltage spikes, it is recommeded to
connect a schottky diode from V
connected to V
1N5817 is recommended for through hole and
MBRS120T3 is recommended for surface mount.
CC
transients, including those produced by output
CC
falls within the V
CC
CC
SO
applied, the M48Z02/12 operates as
that reach into the deselect window
SS
CC
. As V
, anode to V
by as much as one Volt. These
CC
CC
CC
CC
fall time is not less than t
bus. These transients can
bus. The energy stored in
rises, the battery voltage
PFD
PFD
static RAM. Should
SS
CC
(min), the user can
CC
(max), V
). Schottky diode
to V
that drive it to
SS
CC
(cathode
PFD
. There-
(min)
CC
CC
F
.
Figure 9. Checking the BOK Flag Status
Figure 10. Supply Voltage Protection
(BATTERY OK)
V CC
COMPLEMENT BACK
TO SAME ADDRESS
AT ANY ADDRESS
WRITE ORIGINAL
ADDRESS AGAIN
SAME ADDRESS
DATA BACK TO
COMPLEMENT
WRITE DATA
0.1 F
READ DATA
READ DATA
POWER-UP
CONTINUE
AT SAME
OF FIRST
IS DATA
READ?
YES
NO
M48Z02, M48Z12
OF LOW BATTERY
(BATTERY LOW)
NOTIFY SYSTEM
V CC
V SS
(DATA MAY BE
CORRUPTED)
DEVICE
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