Mylex DAC960PG, Installation Manual

Page: 81 / 106

Intelligent Battery Backup Unit
Manual No. 771971 B-3
Functional Description
General Operational Description
The IBBU consists of the following five blocks
1. Electronic switches that connect between V
CC
and the DC-DC
converter output to V
BB
(actual voltage being applied).
2. Power fail (PF) detector that detects the presence or absence of V
CC
.
3. Charger and battery block
4. DC-DC converter to convert 3.6 vdc from the battery to 5 vdc for
backup power.
5. Refresh generator to generate Column Address Strobe (CAS) and Row
Address Strobe (RAS) signals for refresh cycles.
Whenever the system is running, the IBBU is standing by, monitoring the
voltage level of VCC. In the event of a power failure, the VCC voltage level
will begin to drop. When the IBBU detects this voltage drop, it checks the
status of the disk cache. If the cache is empty, the IBBU does nothing.
If the cache contains data during a power failure, it means that there was not
enough time for the cache contents to be written to the disk array. If this is
the case, the data in the cache needs to be preserved. The IBBU immediately
disconnects VCC and connects its own power output to the cache. At the
same time the memory control unit’s RAS and CAS signals are disconnected
from the cache and are replaced by RAS and CAS signals of its own.
The IBBU will maintain cache data integrity until the power is restored.
When power is restored and the system finishes the bootstrap process, the
cache contents will be written to the disk array. The cache contents will then
be flushed from the cache.
Status Indication
The status of the battery can be checked with the gas gauge feature that can
be accessed in GAM (version 2.1x or greater is needed). The gas gauge
appears on the screen as two meters— a battery power meter and a charge
level meter— each calibrated from 0 to 100.