m48t129v STMicroelectronics, m48t129v Datasheet - Page 19

• Manufacturer Part Number: m48t129v
• Description: 5.0 Or 3.3v, 1 Mbit 128 Kbit X 8 Timekeeper Sram
• Manufacturer: STMicroelectronics

Power-on Reset
The M48T129Y/V continuously monitors V
When V
the RST pulls low (open drain) and remains low on
power-up for t
The RST pin is an open drain output and an appro-
priate pull-up resistor to V
control the rise time.
Battery Low Warning
The M48T129Y/V automatically performs battery
voltage monitoring upon power-up and at factory-
programmed time intervals of approximately 24
hours. The Battery Low (BL) Bit, Bit D4 of Flags
Register 1FFF0h, will be asserted if the battery
voltage is found to be less than approximately
2.5V.
If a battery low is generated during a power-up se-
quence, this indicates that the battery is below ap-
proximately 2.5 volts and may not be able to
maintain data integrity in the SRAM. Data should
be considered suspect and verified as correct.
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 V
supplied.
The M48T129Y/V only monitors the battery when
a nominal V
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.
Initial Power-on Defaults
Upon application of power to the device, the fol-
lowing register bits are set to a '0' state: WDS,
BMB0-BMB4, RB0,RB1, AFE, ABE, W, R and FT.
CC
falls to the power fail detect trip point,
CC
REC
is applied to the device. Thus appli-
after V
CC
CC
passes V
should be chosen to
PFD
(max).
CC
CC
is
.
V
I
switching, can produce voltage fluctuations, re-
sulting in spikes on the V
can be reduced if capacitors are used to store en-
ergy which stabilizes the V
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
recommended in order to provide the needed fil-
tering.
In addition to transients that are caused by normal
SRAM operation, power cycling can generate neg-
ative voltage spikes on V
below V
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 V
nected to V
1N5817 is recommended for through hole and
MBRS120T3 is recommended for surface-mount).
Figure 14. Supply Voltage Protection
CC
CC
transients, including those produced by output
Noise And Negative Going Transients
SS
V CC
by as much as one volt. These negative
0.1 F
CC
, anode to V
M48T129Y, M48T129V
CC
CC
CC
bus. These transients
to V
CC
that drive it to values
SS
). (Schottky diode
V CC
V SS
bus. The energy
SS
DEVICE
(cathode con-
Figure
AI02169
14.) is
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