LTC3305EFE Datasheet, PDF (3/8 Pages) Linear Technology – Lead Acid Battery Balancer

DEMO MANUAL DC2043A
OPERATING PRINCIPLE
BAT CURRENT
BATTERY BALANCING CURRENT
0.25V DIFFERENTIAL BETWEEN
BATTERY AND AUX BATTERY
100mA/DIV
Figure 3. Start-Up Battery Balancing Current
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BAT CURRENT
BATTERY BALANCING CURRENT
0.25V DIFFERENTIAL BETWEEN
BATTERY AND AUX BATTERY
100mA/DIV
dc2043a F04
Figure 4. Steady State Battery Balancing Current
Once all batteries in the stack are balanced the DONE pin is
pulled low, the BAL pin is in its high state and the LTC3305
is put into a low power off state. The stack is deemed
balanced when for a four battery stack, the termination
sense comparator detects V_TERMINATE on five consecutive
cycles that connects each of the batteries to the auxiliary
cell using the bottom switches only.
In TIMER mode, the balancing operation continues for a
maximum of the programmed t_ON time. After the t_ON time,
LTC3305 is put into a low power off state for a programmed
t_OFF time, even though the batteries may not be balanced.
Once the t_OFF time expires, the LTC3305 is put into the
ON state and normal operation resumes. The BAL pin is
in its high impedance state if the part is in the OFF state
or when the part is in shutdown.
With the MODE pin set to 1, the LTC3305 will operate in the
CONTINUOUS Mode. The part functions in much the same
way as in the TIMER mode with the following differences.
1. There are no ON or OFF states. The balancing operation
continues even if the stack is in balance. The balanc-
ing operation is terminated only if the part is put into
shutdown. The BAL pin is always pulled low.
2. In CONTINUOUS mode, the top switches are turned
on and balancing operation on a battery is terminated
by the t_BAT time out. Since the auxiliary cell remains
connected to the battery until a t_BAT time out, its volt-
age can change before it connects to the next battery
in the stack. As a result, when the stack is balanced
and the DONE pin is pulled low, the voltages across
individual batteries in the stack may differ by more than
the programmed V_TERMINATE. In the worst case, when
the capacity of the auxiliary cell is much smaller than
the battery, the individual battery voltages will differ by
twice the programmed V_TERMINATE when balanced.
The LTC3305 provides undervoltage and overvoltage
threshold detection that can be programmed using
resistors that are connected between the I_SET, VL and
VH pins and ground. The voltages set on VL and VH are
scaled by a factor of 10, setting the battery undervoltage
and overvoltage thresholds, respectively.
When an undervoltage or overvoltage fault condition is
detected, the corresponding UVFLT or OVFLT pin is pulled
low. The balancing operation is not interrupted during this
time. If the fault condition goes away during balancing, the
corresponding fault pin is put into its high impedance state.
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