LTC3300-1 Datasheet, PDF (15/44 Pages) Linear Technology – High Effciency Bidirectional Multicell Battery Balancer

LTC3300-1
OPERATION
Unidirectional Versus Bidirectional Balancing
Most balancers in use today employ a unidirectional (dis-
charge only) approach. The simplest of these operate by
switching in a resistor across the highest voltage cell(s)
in the stack (passive balancing). No charge is recovered
in this approach -instead it is dissipated as heat in the
resistive element. This can be improved by employing an
energy storage element (inductive or capacitive) to transfer
charge from the highest voltage cell(s) in the stack to other
lower voltage cells in the stack (active balancing). This
can be very efficient (in terms of charge recovery) for the
case where only a few cells in the overall stack are high,
but will be very inefficient (and time consuming) for the
case where only a few cells in the overall stack are low. A
bidirectional active balancing approach, such as employed
by the LTC3300-1, is needed to achieve minimum balanc-
ing time and maximum charge recovery for all common
cell capacity errors.
Synchronous Flyback Balancer
The balancing architecture implemented by the LTC3300‑1
is bidirectional synchronous flyback. Each LTC3300-1
contains six independent synchronous flyback controllers
that are capable of directly charging or discharging an
individual cell. Balance current is scalable with external
components. Each balancer operates independently of
the others and provides a means for bidirectional charge
transfer between an individual cell and a larger group of
adjacent cells. Refer to Figure 2.
Single-Cell Discharge Cycle for Cell 1
Single-Cell Charge Cycle for Cell 1
V_CC
I_CHARGE
I_PRIMARY
V_{TOP_OF_STACK}
5µs
+ _{CELL N}
I_LOAD
I_{PEAK_PRI} = 2A
(I1P = 50mV)
I_SECONDARY
I_{PEAK_SEC} = 2A
(I1S = 50mV)
t
2A
t
~417ns
2A
+ _ISECONDARY
+
CELL 13
(48V)
CELL 12
V_SECONDARY
+
I_PRIMARY
T:1_•
L_PRI
+
10µH
•
V_PRIMARY
CELL 2
(4V)
CELL 1
G1S
G1P
I1S
R_{SNS_SEC}
25mΩ
I1P
R_{SNS_PRI}
25mΩ
–I_SECONDARY
52.05V
t
~417ns
52V
–I_PRIMARY
5µs
50mV
48V
V_PRIMARY
52V
V_SECONDARY
4V 50mV
4V
t
48V
50mV
48V
52V
50mV
51.95V
V_SECONDARY
50mV
t
V_PRIMARY
4V
50mV
t
52V
48V
t
4V
t
33001 F02
Figure 2. Synchronous Flyback Balancing Example with T = 1, S = 12
For more information www.linear.com/product/LTC3300-1
33001f
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