M48Z32VMT datasheet(8/16 Pages) STMICROELECTRONICS

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M48Z32V

8/16

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

AI02169

VCC

0.1

µF

DEVICE

VCC

VSS

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