M48T35_0708 datasheet(11/29 Pages) STMICROELECTRONICS

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M48T35 M48T35Y

Operation modes

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2.3

Data retention mode

With valid VCC applied, the M48T35/Y operates as a conventional BYTEWIDE static RAM.

Should the supply voltage decay, the RAM will automatically 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” (see Figure 12 on

page 19, Table 10, and Table 11 on page 20).

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 content. 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 M48T35/Y may respond to transient noise spikes on VCC that reach

into the deselect window during the time the device 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 which

preserves data and powers the clock. The internal button cell will maintain data in the

M48T35/Y for an accumulated period of at least 7 years 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 protection continues until VCC reaches VPFD (min)

plus trec (min). E should be kept high as VCC rises past VPFD (min) to prevent inadvertent

WRITE Cycles prior to processor stabilization. Normal RAM operation can resume trec after

VCC exceeds VPFD (max).

For more information on Battery Storage Life refer to the Application Note AN1012.

tWLWH

WRITE Enable Pulse Width

tELEH

Chip Enable Low to Chip Enable High

tWHAX

WRITE Enable High to Address Transition

tEHAX

Chip Enable High to Address Transition

tDVWH

Input Valid to WRITE Enable High

tDVEH

Input Valid to Chip Enable High

tWHDX

WRITE Enable High to Input Transition

tEHDX

Chip Enable High to Input Transition

tWLQZ

(2)(3)

WRITE Enable Low to Output Hi-Z

tAVWH

Address Valid to WRITE Enable High

tAVEH

Address Valid to Chip Enable High

tWHQX

(2)(3)

WRITE Enable High to Output Transition

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

noted).

CL = 5pF.

If E goes low simultaneously with W going low, the outputs remain in the high impedance state.

Table 4.

Write mode AC characteristics (continued)

Symbol

Parameter(1)

M48T35/Y

Unit

Min

Max

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