M48T08 datasheet(13/31 Pages) STMICROELECTRONICS

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M48T08, M48T08Y, M48T18

Operation modes

Doc ID 2411 Rev 11

13/31

2.3

Data retention mode

With valid VCC applied, the M48T08/18/08Y 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.”

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 M48T08/18/08Y 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

M48T08/18/08Y for an accumulated period of at least 10 years when VCC is less than VSO.

Note:

Requires use of M4T32-BR12SH SNAPHAT® top when using the SOH28 package.

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). E1 should be kept

high or E2 low as VCC rises past VPFD (min) to prevent inadvertent WRITE cycles prior to

system 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.

2.4

Power-fail interrupt pin

The M48T08/18/08Y continuously monitors VCC. When VCC falls to the power-fail detect trip

point, an interrupt is immediately generated. An internal clock provides a delay of between

10 µs and 40 µs before automatically deselecting the M48T08/18/08Y. The INT pin is an

open drain output and requires an external pull-up resistor, even if the interrupt output

function is not being used.

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