M48Z129V datasheet(9/16 Pages) STMICROELECTRONICS

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M48Z129Y*, M48Z129V

Data Retention Mode

With valid VCC applied, the M48Z129Y/V operates

as a conventional BYTEWIDE™ static RAM.

Should the supply voltage decay, the RAM will au-

tomatically deselect, write protecting itself when

VCC falls between VPFD (max), VPFD (min) win-

dow. 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 current addressed location, but

does not jeopardize the rest of the RAM’s content.

At voltages below VPFD(min), the memory will be

in a write protected state, provided the VCC fall

time is not less than tF. The M48Z129Y/V may re-

spond to transient noise spikes on VCC that cross

into the deselect window during the time the de-

vice is sampling VCC. Therefore, decoupling of the

power supply lines is recommended.

When VCC drops below VSO, the control circuit

switches power to the internal battery, preserving

data. The internal energy source will maintain data

in the M48Z129Y/V for an accumulated period of

at least 10 years at room temperature. As system

power rises above VSO, the battery is disconnect-

ed, and the power supply is switched to external

VCC. Deselect continues for tREC after VCC reach-

es 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 (as shown in Figure

9.) is recommended 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, 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.

Figure 9. Supply Voltage Protection

AI02169

VCC

0.1

µF

DEVICE

VCC

VSS

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