M40Z300MH datasheet(8/16 Pages) STMICROELECTRONICS

8 / 16 page

M40Z300, M40Z300W

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Table 7. Power Down/Up AC Characteristics

(TA = 0 to 70°C)

Note: 1. VPFD (max) to VPFD (min) fall time of less than tF may result in deselection/write protection not occurring until 200 µs after

VCC passes VPFD (min)..

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

Symbol

Parameter

Min

Max

Unit

(1)

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

300

µs

tFB

(2)

VPFD (min) to VSS VCC Fall Time

150

µs

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

µs

tEDL

Chip Enable Propagation Delay Low

M40Z300

M40Z300W

tEDH

Chip Enable Propagation Delay High

M40Z300

M40Z300W

tAS

A, B set up to E

0ns

tCER

Chip Enable Recovery

120

tREC

VPFD (max) to RST High

120

tWPT

Write Protect Time

M40Z300

150

µs

M40Z300W

250

µs

tRB

VSS to VPFD (min) VCC Rise Time

1µs

BATTERY LOW PIN

The M40Z300/W automatically performs battery

voltage monitoring upon power-up, and at factory-

programmed time intervals of at least 24 hours.

The Battery Low (BL) pin will be asserted if the

battery voltage is found to be less than approxi-

mately 2.5V. The BL pin will remain asserted until

completion of battery replacement and subse-

quent battery low monitoring tests, either during

the next power-up sequence or the next scheduled

24-hour interval.

If a battery low is generated during a power-up se-

quence, this indicates that the battery is below

2.5V and may not be able to maintain data integrity

in the SRAM. Data should be considered suspect,

and verified as correct. A fresh battery should be

installed.

If a battery low indication is generated during the

24-hour interval check, this indicates that the bat-

tery is near end of life. However, data is not com-

promised due to the fact that a nominal VCC is

supplied. In order to insure data integrity during

subsequent periods of battery back-up mode, the

battery should be replaced. SNAPHAT top should

be replaced with valid VCC applied to the device.

The M40Z300/W only monitors the battery when a

nominal VCC is applied to the device. Thus appli-

cations which require extensive durations in the

battery back-up mode should be powered-up peri-

odically (at least once every few months) in order

for this technique to be beneficial. Additionally, if a

battery low is indicated, data integrity should be

verified upon power-up via a checksum or other

technique. The BL pin is an open drain output and

an appropriate pull-up resistor to VCC should be

chosen to control the rise time.

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