M48Z32V 查看數據表（PDF） - STMicroelectronics
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M48Z32V Datasheet PDF : 16 Pages
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M48Z32V
Data Retention Mode
With valid VCC applied, the M48Z32V operates as
a conventional BYTEWIDE™ static RAM. Should
the supply voltage decay, the RAM will automati-
cally 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 con-
tent. 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 M48Z32V 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 external battery which pre-
serves data.
As system power returns and VCC rises above
VSO, the battery is disconnected, and the power
supply is switched to external VCC. Write protec-
tion continues 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.
VCC Noise And Negative Going Transients
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 (see Figure 8) is rec-
ommended in order to provide the needed 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 negative
spikes can cause data corruption in the SRAM
while in battery backup mode. To protect from
these voltage spikes, ST recommends connecting
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).
Figure 8. Supply Voltage Protection
VCC
VCC
0.1µF
DEVICE
VSS
AI02169
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