M48Z35AV-100PC1TR View Datasheet(PDF) - STMicroelectronics
Part Name
Description
Manufacturer
M48Z35AV-100PC1TR Datasheet PDF : 16 Pages
| |||
M48Z35AY, M48Z35AV
Figure 9. Checking the BOK Flag Status
POWER-UP
READ DATA
AT ANY ADDRESS
WRITE DATA
COMPLEMENT BACK
TO SAME ADDRESS
READ DATA
AT SAME
ADDRESS AGAIN
Figure 10. Supply Voltage Protection
VCC
0.1µF
VCC
DEVICE
VSS
AI02169
IS DATA
COMPLEMENT
OF FIRST
READ?
(BATTERY OK) YES
WRITE ORIGINAL
DATA BACK TO
SAME ADDRESS
NO (BATTERY LOW)
NOTIFY SYSTEM
OF LOW BATTERY
(DATA MAY BE
CORRUPTED)
CONTINUE
AI00607
Also, as VCC rises, the battery voltage is checked.
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.
POWER SUPPLY DECOUPLING and
UNDERSHOOT PROTECTION
ICC transients, including those produced by output
switching, can produce voltage fluctuations, re-
sulting in spikes on the VCC bus. These transients
can be reduced if capacitors are used to store en-
ergy, which stabilizes the VCC bus. The energy
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 VCC that drive it to values
below VSS by as much as one Volt. These nega-
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 VCC to VSS (cathode
connected to VCC, anode to VSS). Schottky diode
1N5817 is recommended for through hole and
MBRS120T3 is recommended for surface mount.
10/16
|
|
Share Link: 