M48Z35AV ST Microelectronics, M48Z35AV Datasheet - Page 10

• Manufacturer Part Number: M48Z35AV
• Description: 256 Kbit 32Kb x8 ZEROPOWER SRAM
• Manufacturer: ST Microelectronics

M48Z35AY, M48Z35AV
Figure 9. Checking the BOK Flag Status
Also, as V
If the voltage is less than approximately 2.5V, 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 illustrates how a BOK check routine could
be structured.
For more information on Battery Storage Life refer
to the Application Note AN1012.
10/16
(BATTERY OK)
COMPLEMENT BACK
TO SAME ADDRESS
AT ANY ADDRESS
ADDRESS AGAIN
WRITE ORIGINAL
CC
SAME ADDRESS
DATA BACK TO
COMPLEMENT
WRITE DATA
READ DATA
READ DATA
POWER-UP
CONTINUE
AT SAME
OF FIRST
rises, the battery voltage is checked.
IS DATA
READ?
YES
NO
OF LOW BATTERY
(BATTERY LOW)
NOTIFY SYSTEM
(DATA MAY BE
CORRUPTED)
AI00607
Figure 10. Supply Voltage Protection
POWER SUPPLY DECOUPLING and
UNDERSHOOT PROTECTION
I
switching, can produce voltage fluctuations, re-
sulting in spikes on the V
can be reduced if capacitors are used to store en-
ergy, which stabilizes the V
stored in the bypass capacitors will be released as
low going spikes are generated or energy will be
absorbed when overshoots occur. A ceramic by-
pass capacitor value of 0.1µF (as shown in Figure
10) is recommended in order to provide the need-
ed filtering.
In addition to transients that are caused by normal
SRAM operation, power cycling can generate neg-
ative voltage spikes on V
below V
tive spikes can cause data corruption in the SRAM
while in battery backup mode. To protect from
these voltage spikes, it is recommended to con-
nect 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
V CC
SS
by as much as one Volt. These nega-
0.1 F
CC
, anode to V
CC
CC
bus. These transients
that drive it to values
CC
CC
SS
V CC
V SS
bus. The energy
). Schottky diode
to V
DEVICE
SS
AI02169
(cathode