134
Power Delivery
9.3
Battery Backup
With a self-refresh command the DDR is able to store data. After a self-refresh command, the DDR
refreshes itself autonomously with internal logic and timers. The DDR SDRAM remains in
self-refresh mode as long as
CKE[1:0]
are low. CKE signals will stay low providing the DDR
voltage is not removed from 80331. If 80331 is isolated from the DDR battery voltage it is
recommended that the CKE circuit shown in
be implemented. The
CKE
latch circuitry
in
is battery powered. It allows maintaining the
CKE[1:0]
signals low while the system
power is off. The latches are cleared when the 80331 drives
CKE[1:0]
low with a self-refresh
command and are reset when
PWRGD
is driven from low to high after system power is recovered.
During normal operation, the
CKE
signals are controlled by the 80331. When the power is turned
off, the battery powered latches pull the
CKE
signals low using the two transistors.
Note:
It is recommended that the power planes for battery backup and the IOP power be isolated to avoid
battery drain due to leakage when in battery backup mode. This can be implemented with a FET
that isolates these planes during battery backup mode.
Figure 68.
SCKE Circuit
Summary of Contents for 80331
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