Mylex DAC960PG, Installation Manual

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Battery Backup Capacity
B-8 DAC960PG Installation Guide
Battery Backup Capacity
Battery backup capacity is defined as the maximum duration of a power
failure for which data in the cache can be maintained by the battery. The
IBBU’s backup capacity varies with the memory configuration installed on
the DAC960PG. Battery backup capacity can be reasonably expected
according to Tabe 4-1
Table 4-1. IBBU Capacity vs. Cache Memory Configuration
Calculations for Battery Duration
The backup capacity of the battery (in hours) on the IBBU module is
calculated using the following formula:
Duration in hours = B / (I
SIMM
+ I
P
)
Where:
B = battery capacity in mAh (= 600 for the battery on the IBBU)
I
SIMM
= SIMM current in mA @ 5V
This is derived from the average of I
CBR
, or SIMM current during CAS before
RAS @ 130ns / 16µs (= .008125) times SIMM voltage (= 5V), all divided by
battery voltage (= 3.6V) times the DC-DC effieicncy coefficient (= .85).
or:
I
SIMM
= (I
CBR
x .008125 x 5) / (3.6 x .85)
= (I
CBR
x .040625) / 3.06
I
P
= IBBU current (2mA max) @ 3.6V
Therefore the Duration in hours = 600 / (I
SIMM
+ 2)
Capacity Mem Type Battery Backup
Duration (Min)
4 MB EDO ECC RAM 50 hours
8 MB EDO ECC RAM 25 hours
16 MB EDO ECC RAM 35 hours
32 MB EDO ECC RAM 15 hours
64 MB EDO ECC RAM 25 hours
128 MB EDO ECC RAM 15 hours