Z-World Fox LP3500, User Manual

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122 Fox (LP3500)
E.2.1 Replacing the Backup Battery
The battery is user-replaceable, and is fitted in a battery holder. To replace the battery, lift
up on the spring clip and slide out the old battery. Use only a Panasonic CR2330 or equiv-
alent replacement battery, and insert it into the battery holder with the + side facing up.
NOTE: The SRAM contents and the real-time clock settings will be lost if the battery is
replaced with no power applied to the LP3500. Exercise care if you replace the battery
while external power is applied to the LP3500.
NOTE: Should it be more convenient, it is also possible to install the onboard battery on
the other side of the LP3500 board.
CAUTION: There is an explosion danger if the battery is short-circuited, recharged, or
replaced incorrectly. Replace the battery only with the same type or an equivalent type
recommended by the battery manufacturer. Dispose of used batteries according to the
battery manufacturer’s instructions.
E.2.2 Power to VRAM Switch
The VRAM switch on the LP3500 module, shown in Figure E-3, allows the battery
backup to provide power when the external power goes off. The switch provides an isola-
tion between Vcc and the battery when Vcc goes low. This prevents the Vcc line from
draining the battery.
Figure E-3. VRAM Switch
Field-effect transistor Q12 provides a very small voltage drop between Vcc and VRAM
(<100 mV, typically 10 mV) so that the board components powered by Vcc will not have a
significantly different voltage than VRAM.
When the LP3500 is not in reset, the /RESOUT line will be high. This allows VRAM to
nearly equal Vcc.
When the LP3500 is in reset, the /RESOUT line will go low. This provides an isolation
between Vcc and VRAM.
RESOUT
Q12
R46
/CS
220 k W
Vcc
10 nF
C62
VRAM