M48Z35 datasheet(12/20 Pages) STMICROELECTRONICS

12 / 20 page

M48Z35, M48Z35Y

12/20

Data Retention Mode

With valid VCC applied, the M48Z35/Y 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 M48Z35/Y 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. The internal button cell will maintain

data in the M48Z35/Y for an accumulated period of

at least 10 years (at 25°C) 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 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.

Figure 11. Power Down/Up Mode AC Waveforms

Table 9. Power Down/Up AC Characteristics

Note: 1. Valid for Ambient Operating Temperature: TA = 0 to 70°C or –40 to 85°C; VCC = 4.75 to 5.5V or 4.5 to 5.5V (except where noted).

2. VPFD (max) to VPFD (min) fall time of less than tF may result in deselection/write protection not occurring until 200µs after VCC pass-

es VPFD (min).

3. VPFD (min) to VSS fall time of less than tFB may cause corruption of RAM data.

4. tREC (min) = 20ms for industrial temperature Grade (6) device.

Symbol

Parameter(1)

Min

Max

Unit

tPD

E or W at VIH before Power Down

0µs

(2)

VPFD (max) to VPFD (min) VCC Fall Time

300

µs

tFB

(3)

VPFD (min) to VSS VCC Fall Time

µs

VPFD (min) to VPFD (max) VCC Rise Time

µs

tRB

VSS to VPFD (min) VCC Rise Time

1µs

tREC

(4)

VPFD (max) to Inputs Recognized

200

AI01168C

VCC

INPUTS

(PER CONTROL INPUT)

OUTPUTS

DON'T CARE

HIGH-Z

tFB

tPD

tRB

tDR

VALID

(PER CONTROL INPUT)

RECOGNIZED

VPFD (max)

VPFD (min)

VSO

tREC

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