m48t37v STMicroelectronics, m48t37v Datasheet - Page 18

• Manufacturer Part Number: m48t37v
• Description: 5.0 Or 3.3v, 256 Kbit 32 Kbit X 8 Timekeeper Sram
• Manufacturer: STMicroelectronics

3.10
3.11
18/29
which require extensive durations in the battery back-up mode should be powered-up
periodically (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 following register bits are set to a '0' state:
WDS; BMB0-BMB4; RB0-RB1; AFE; ABE; W; R; and FT (see
Table 7.
1. WDS, BMB0-BMB4, RBO, RB1.
2. State of other control bits undefined.
3. State of other control bits remains unchanged.
4. Assuming these bits set to '1' prior to power-down.
V
I
fluctuations, resulting in spikes on the V
capacitors are used to store energy which stabilizes the V
bypass capacitors will be released as low going spikes are generated or energy will be
absorbed when overshoots occur. A ceramic bypass capacitor value of 0.1µF (as shown in
Figure
In addition to transients that are caused by normal SRAM operation, power cycling can
generate negative voltage spikes on V
one volt. These negative spikes can cause data corruption in the SRAM while in battery
backup mode. To protect from these voltage spikes, it is recommended to connect a
schottky diode from V
1N5817 is recommended for through hole and MBRS120T3 is recommended for surface
mount.
Initial Power-up
(Battery Attach for SNAPHAT)
Subsequent Power-up / RESET
Power-down
CC
CC
transients, including those produced by output switching, can produce voltage
noise and negative going transients
9) is recommended in order to provide the needed filtering.
Condition
(4)
Default values
CC
to V
(2)
SS
(3)
(cathode connected to V
W
0
0
0
CC
CC
that drive it to values below V
bus. These transients can be reduced if
R
0
0
0
FT
0
0
0
CC
CC
AFE
, anode to V
0
0
1
bus. The energy stored in the
Table
ABE
7).
0
0
1
SS
SS
by as much as
). Schottky diode
WATCHDOG
Register
0
0
0
(1)