3
dc2043bfb
DEMO MANUAL DC2043B
OPERATING PRINCIPLE
2.0s/DIV
BATX
5.00V/DIV
BATY
5.00V/DIV
AUX BATTERY
CURRENT
200mA/DIV
dc2043 F03
2.0s/DIV
BATX
5.00V/DIV
BATY
5.00V/DIV
AUX BATTERY
CURRENT
200mA/DIV
dc2043 F04
Figure 3. Start-Up Battery Balancing Current
Figure 4. Steady State Battery Balancing Current
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.
A number of components are included on the DC2043B
to protect the circuit from damage when hot-plugging the
battery connections to the board.
Clamping diode D100 prevents the BOOST pin on the
LTC3305 from going excessively negative with respect
to the V4 pin during hot plug. Likewise, D101 prevents
the voltage at the CP pin from going excessively negative
with respect to the CP pin.
Antiparallel Schottky diodes and a 100Ω resistor tie each
power connection with its corresponding sense (Kelvin)
connection. The resistor keeps the potential between the
power and sense connections near zero while the diodes
maintain the voltage difference to a few tenths of a volt
even when transient currents want to flow between power
and sense connections.