LTC3305EFE Datasheet, PDF (2/8 Pages) Linear Technology – Lead Acid Battery Balancer

DEMO MANUAL DC2043A
Performance Summary
SYMBOL
V_BAT
V_TERMINATE
V_TERMINATE
V_TERMINATE
V_TERMINATE
V_REG
PARAMETER
Battery Voltage Range
Termination Voltage Range
Termination Voltage Range
Termination Voltage Range
Termination Voltage Range
Regulator Output Voltage Range
Specifications are at T_A = 25°C
CONDITIONS
TERM2 = 0, TERM1 = 0
TERM2 = 0, TERM1 = 1
TERM2 = 1, TERM1 = 0
TERM2 = 1, TERM1 = 1
I_VREG = 200µA
MIN
MAX
UNITS
4.0
to
16.0
V
±5
to
±20
mV
±17.5
to
±32.5
mV
±42.5
to
±57.5
mV
±90
to
±110
mV
2.4
to
2.6
V
OPERATING PRINCIPLE
Refer to the block diagram within the LTC3305 data sheet
for its operating principle.
The LTC3305 balances batteries using an auxiliary cell
or an alternate storage cell as a charge reservoir. The
LTC3305 controls external N Channel MOSFET switches
in a preprogrammed sequence to connect a battery in the
stack to an auxiliary cell. Charge is transferred to or from
the auxiliary cell when it is connected to a battery.
The LTC3305 can operate in one of two modes, TIMER
mode or CONTINUOUS mode, programmable via the
MODE pin. Balancing operation begins once the CBOOST
capacitor is charged to at least 6.95V. The EN1 and EN2
pins select the number of batteries in the stack.
EN1
EN2
Application
0
0
SHUTDOWN
0
1
2 Battery Stack
1
0
3 Battery Stack
1
1
4 Battery Stack
With the MODE pin set to 0 the LTC3305 will operate in the
TIMER Mode. The BAL pin will be pulled low, indicating
that the part is enabled and balancing the battery stack.
The balancing operation begins with the terminal of the
auxiliary cell connected to the negative terminal of BAT1,
the lowest battery in the stack. The bottom switches that
connect the negative terminals of BAT1 to the Auxiliary
cell’s negative terminal are turned on. After a 50ms delay,
the voltages across the auxiliary cell and BAT1 are com-
pared by the termination sense comparator. If the voltage
difference between the auxiliary cell and BAT1 is less than
the selected termination voltage, the battery is deemed to
be in a balance state with respect to the auxiliary cell. The
bottom switches will be turned off and the next battery
within the stack will be connected.
If the voltage difference between the auxiliary cell and
BAT1 is greater than the selected termination voltage, the
top switches that connect the positive terminal of BAT1
to the auxiliary cell’s positive terminals through the PTC
thermistor are turned on. Current is limited by the PTC
thermistor. Figure 3 shows the startup battery current
where the PTC is limiting as it heats up. Figure 4 is the
steady state battery current after the PTC has reached its
thermal equilibrium. After a 50ms delay, the termination
sense comparator starts to monitor the voltage across
the auxiliary cell and the battery. The battery will remain
connected to the auxiliary cell until the voltage difference
decreases to the selected termination voltage or a t_BAT
timeout occurs.
At this point all switches are turned off and the second
battery in the stack will be connected to the auxiliary cell
after a 50ms delay. This 50ms delay provides a break be-
fore make function before the next battery is connect-ed.
The cycle will be repeated for each battery in the stack.
dc2043af
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