LTC3300-2
22
33002f
For more information www.linear.com/LTC3300-2
OPERATION
ACTIVE
5.6V
LTC3300-2
V
REG
WDT
RTONS
R
TONS
33002 F06a
V
–
1.2V
R
TONS
R
WDT
ACTIVE
5.6V
LTC3300-2V
TH
= 1.4V
V
REG
WDT
RTONS
R
TONS
PAUSE/
RESUME
33002 F06b
1.2V
R
TONS
ACTIVE
5.6V
V
REG
V
REG
TO TRANSFORMER
SECONDARY WINDINGS
LTC3300-2
WDT
RTONS
R
TONS
V
REG
V
REG
PAUSE/
RESUME
EITHER/OR
PAUSE/
RESUME
33002 F06c
1.2V
R
TONS
R
SEC_OVP
(6a) Watchdog Timer Only (WDT = V
–
to Defeat) (6b) Pause/Resume Balancing Only
(6c) Watchdog Timer with Pause/Resume Balancing and Secondary Winding OVP Protection
Figure 6. WDT Pin Connection Options
Secondary Winding OVP Function (via WDT pin)
The precision current source pull-down on the WDT pin
during balancing can be used to construct an accurate
secondary winding OVP protection circuit as shown in
Figure 6c. A second external resistor, scaled to R
TONS
and connected to the transformer secondary winding, is
used to set the comparator threshold. An NMOS cascode
device (with gate tied to V
REG
) is also needed to protect
the WDT pin from high voltage. The secondary winding
OVP thresholds are given by:
V
SEC|OVP(RISING)
= 1.4V + 1.2V • (R
SEC_OVP
/R
TONS
)
V
SEC|OVP(FALLING)
= 1.4V + 1.05V • (R
SEC_OVP
/R
TONS
)
This comparator will protect the LTC3300-2 application
circuit if the secondary winding connection to the battery
stack is lost while balancing and the secondary winding
voltage is still increasing as a result of that balancing. The
balance command remains stored in memory, and active
balancing will resume where it left off if the stack voltage
subsequently falls to a safer level.
Single
Transformer Application (CTRL = V
REG
)
Figure 7 shows a fully populated LTC3300-2 application
employing all six balancers with a single shared custom
transformer. In this application, the transformer has six
primary windings coupled to a single secondary winding.
Only one balancer can be active at a given time as all six
share the secondary gate driver G1S and secondary current
sense input I1S. The unused gate driver outputs G2S-G6S
must be left floating and the unused current sense inputs
I2S-I6S should be connected to V
–
. Any balance command
which attempts to operate more than one balancer at a time
will be ignored. This application represents the minimum
component count active balancer achievable.
