LTC3300-1 Datasheet, PDF (34/44 Pages) Linear Technology – High Effciency Bidirectional Multicell Battery Balancer

LTC3300-1
APPLICATIONS INFORMATION
Battery Interconnection Integrity
The FMEA scenarios involving a break in the stack of battery
cells are potentially the most damaging. In the case where
the battery stack has a discontinuity between groupings
of cells balanced by LTC3300-1 ICs, any load will force a
large reverse potential on the daisy-chain connection. This
situation might occur in a modular battery system during
initial installation or a service procedure. The daisy-chain
ports are protected from the reverse potential in this
scenario by external series high voltage diodes required
in the upper port data connections as shown in Figure 13.
During the charging phase of operation, this fault would
lead to forward biasing of daisy-chain ESD clamps that
would also lead to part damage. An alternative connection
to carry current during this scenario will avoid this stress
from being applied (Figure 13).
Internal Protection Diodes
Each pin of the LTC3300-1 has protection diodes to help
prevent damage to the internal device structures caused
by external application of voltages beyond the supply rails
as shown in Figure 14. The diodes shown are conventional
silicon diodes with a forward breakdown voltage of 0.5V.
The unlabeled Zener diode structures have a reverse-
breakdown characteristic which initially breaks down at
9V then snaps back to a 7V clamping potential. The Zener
diodes labeled Z_CLAMP are higher voltage devices with an
initial reverse breakdown of 25V snapping back to 22V.
The forward voltage drop of all Zeners is 0.5V.
The internal protection diodes shown in Figure 14 are
power devices which are intended to protect against
limited-power transient voltage excursions. Given that
these voltages exceed the absolute maximum ratings of
the LTC3300-1, any sustained operation at these voltage
levels will damage the IC.
Initial Battery Connection to LTC3300-1
In addition to the above-mentioned internal protection
diodes, there are additional lower voltage/lower current
diodes across each of the six differential cell inputs (not
shown in Figure 14) which protect the LTC3300-1 during
initial installation of the battery voltages in the application.
These diodes have a breakdown voltage of 5.3V with 20kΩ
of series resistance and keep the differential cell voltages
below their absolute maximum rating during power-up
when the cell terminal currents are zero to tens of mi-
croamps. This allows the six batteries to be connected in
any random sequence without fear of an unconnected cell
input pin overvoltaging due to leakage currents acting on
its high impedance input. Differential cell-to-cell bypass
capacitors used in the application must be of the same
nominal value for full random sequence protection.
+
LTC3300-1
V^–
(NEXT HIGHER IN STACK)
PROTECT
AGAINST
BREAK
HERE
OPTIONAL
REDUNDANT
CURRENT
PATH
SDO SDI SCKI CSBI
RSO7J
×3
SDOI SCKO CSBO
+
C6
LTC3300-1
(NEXT LOWER IN STACK)
33001 F13
Figure 13. Reverse-Voltage Protection for the Daisy Chain (One Link Connection Shown)
34
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33001f