M48Z2M1Y datasheet(9/17 Pages) STMICROELECTRONICS

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M48Z2M1Y, M48Z2M1V

Data Retention Mode

With valid VCC applied, the M48Z2M1Y/V oper-

ates as a conventional BYTEWIDE™ static RAM.

Should the supply voltage decay, the RAM will au-

tomatically power-fail deselect, write protecting it-

self 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 cells will maintain data in the

M48Z2M1Y/V after the initial application of VCC 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 batteries are 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.

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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