M48Z58-70PC6 Просмотр технического описания (PDF) - STMicroelectronics
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M48Z58-70PC6 Datasheet PDF : 17 Pages
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M48Z58, M48Z58Y
DATA RETENTION MODE
With valid VCC applied, the M48Z58/58Y operates
as a conventional BYTEWIDE™ static RAM.
Should the supply voltage decay, the RAM will
automatically power-fail deselect, write protecting
itself when VCC f alls 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
content. 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 M48Z58/58Y may respond to transient noise
spikes on VCC that reach into the deselect window
during the time the device is sampling VCC. There-
fore, decoupling of the power supply lines is rec-
ommended.
When VCC drops below VSO, the control circuit
switches power to the internal battery which pre-
serves data. The internal button cell will maintain
data in the M48Z58/58Y for an accumulated period
of at least 10 years when VCC is less than VSO.
As system power returns and VCC rises above VSO,
the battery is disconnected, and the power supply
is switched to external VCC. Write protection con-
tinues until VCC reaches VPFD(min) plus tREC(min).
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 SUPPLY DECOUPLING and UNDER-
SHOOT PROTECTION
ICC transients, including those produced by output
switching, can produce voltage fluctuations, result-
ing in spikes on the VCC bus. These transients can
be reduced if capacitors are used to store energy,
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 bypass capaci-
tor value of 0.1µF (as shown in Figure 9) is recom-
mended in order to provide the needed filtering.
In addition to transients that are caused by normal
SRAM operation, power cycling can generate
negative voltage spikes on VCC that drive it to
values below VSS by as much as one Volt. These
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 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.
Figure 9. Supply Voltage Protection
VCC
0.1µF
VCC
DEVICE
VSS
AI02169
9/17
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