M48Z08MH 查看數據表（PDF） - STMicroelectronics
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M48Z08MH Datasheet PDF : 18 Pages
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M48Z08, M48Z18
DATA RETENTION MODE
With valid VCC applied, the M48Z08/18 operates as
a conventional BYTEWIDE™ static RAM. Should
the supply voltage decay, the RAM will automat-
ically power-fail deselect, write protecting itself
when VCC falls within the VPFD(max), VPFD(min)
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 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 M48Z08/18 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 and powers the clock. The internal
button cell will maintain data in the M48Z08/18 for
an accumulated period of at least 11 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 continues until VCC reaches VPFD
(min) plus tREC (min). E should be kept high as VCC
rises past VPFD(min) to prevent inadvertent write
cycles prior to system stabilization. Normal RAM
operation can resume tREC after VCC exceeds
VPFD(max).
For more information on Battery Storage Life refer
to the Application Note AN1012.
SYSTEM BATTERY LIFE
The useful life of the battery in the M48Z08/18 is
expected to ultimately come to an end for one of
two reasons: either because it has been dis-
charged while providing current to the RAM in the
battery back-up mode, or because the effects of
aging render the cell useless before it can actually
be completely discharged. The two effects are
virtually unrelated, allowing discharge or Capacity
Consumption, and the effects of aging or Storage
Life, to be treated as two independent but simulta-
neous mechanisms. The earlier occurring failure
mechanism defines the battery system life of the
M48Z08/18.
Figure 9. Predicted Battery Storage Life versus Temperature
AI01399
50
40
t50% (AVERAGE)
30
t1%
20
10
8
6
5
4
3
2
1
20
30
40
50
60
70
80
90
TEMPERATURE (Degrees Celsius)
9/18
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