2
dc2043bfb
DEMO MANUAL DC2043B
OPERATING PRINCIPLE
Refer to the block diagram within the LTC3305 data sheet
for its operating principle.
The LTC3305 balances batteries using an auxiliary battery
or an alternate storage means as a charge reservoir. The
LTC3305 controls external N Channel MOSFET switches
in a preprogrammed sequence to connect a battery in
the stack to the auxiliary battery. Charge is transferred
to or from the auxiliary battery when it is connected to a
battery in the stack.
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 battery 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
battery's negative terminal are turned on. After a 50ms
delay, the voltages across the auxiliary battery and BAT1
are compared by the termination sense comparator. If the
voltage difference between the auxiliary battery and BAT1
is less than the selected termination voltage, the battery
is deemed to be in a balance state with respect to the
auxiliary battery. The bottom switches will be turned off
and the next battery within the stack will be connected.
If the voltage difference between the auxiliary battery and
BAT1 is greater than the selected termination voltage, the
top switches that connect the positive terminal of BAT1
to the auxiliary battery’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 battery and the battery. The battery will remain
connected to the auxiliary battery until the voltage differ-
ence 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 bat-
tery after a 50ms delay. This 50ms delay provides a break-
before-make function before the next battery is connected.
The cycle will be repeated for each battery in the stack.
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 bal-
anced when for a four battery stack, the termination-sense
comparator detects V
TERMINATE
on five consecutive cycles
that connect each of the batteries to the auxiliary battery
using the bottom switches only.
PERFORMANCE SUMMARY
Specifications are at T
A
= 25°C
SYMBOL
PARAMETER
CONDITIONS
MIN
MAX
UNITS
V
BAT
Battery Voltage Range
4.0
to
16.0
V
V
TERMINATE
Termination Voltage Range
TERM2 = 0, TERM1 = 0
±5
to
±20
mV
V
TERMINATE
Termination Voltage Range
TERM2 = 0, TERM1 = 1
±17.5
to
±32.5
mV
V
TERMINATE
Termination Voltage Range
TERM2 = 1, TERM1 = 0
±42.5
to
±57.5
mV
V
TERMINATE
Termination Voltage Range
TERM2 = 1, TERM1 = 1
±90
to
±110
mV
V
REG
Regulator Output Voltage Range
I
VREG
= 200µA
2.4
to
2.6
V
