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M48Z512AY-70PM9 View Datasheet(PDF) - STMicroelectronics

Part Name
Description
Manufacturer
M48Z512AY-70PM9
ST-Microelectronics
STMicroelectronics ST-Microelectronics
M48Z512AY-70PM9 Datasheet PDF : 17 Pages
First Prev 11 12 13 14 15 16 17
M48Z512A, M48Z512AY
Figure 11. Supply Voltage Protection
VCC
0.1µF
VCC
DEVICE
VSS
AI02169
DATA RETENTION MODE
With valid VCC applied, the M48Z512A/512AY op-
erates as a conventional BYTEWIDEstatic
RAM. Should the supply voltage decay, the RAM
will automatically power-fail deselect, write pro-
tecting itself tWP after VCC falls below VPFD. All
outputs become high impedance, and all inputs
are treated as ”don’t care.”
If power fail detection occurs during a valid ac-
cess, the memory cycle continues to completion. If
the memory cycle fails to terminate within the time
tWP, write protection takes place. When VCC drops
below VSO, the control circuit switches power to
the internal energy source which preserves data.
The internal coin cell will maintain data in the
M48Z512A/512AY after the initial application of
VCC for an accumulated period of at least 10 years
when VCC is less than VSO. As system power re-
turns and VCC rises above VSO, the battery is dis-
connected, and the power supply is switched to
external VCC. Write protection continues for tER af-
ter VCC reaches VPFD to allow for processor stabi-
lization. After tER, normal RAM operation can
resume.
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
11) 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 recommeded to connect
a schottky diode from VCC to VSS (cathode con-
nected to VCC, anode to VSS). Schottky diode
1N5817 is recommended for through hole and
MBRS120T3 is recommended for surface mount.
11/17
 

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