Using The Ltc6804 With Less Than 12 Cells - Linear Technology LTC6804-1 Manual

applicaTions inForMaTion

USING THE LTC6804 WITH LESS THAN 12 CELLS

If the LTC6804 is powered by the battery stack, the
minimum number of cells that can be monitored by the
LTC6804 is governed by the supply voltage requirements
+
of the LTC6804. V must be at least 11V to properly
bias the LTC6804. Figure 40 shows an example of the
LTC6804 when used to monitor eight cells with best cell
measurement synchronization. The 12 cells monitored by
the LTC6804 are split into two groups of 6 cells and are
measured using two internal multiplexers and two ADCs.
To optimize measurement synchronization in applications
with less than 12 Cells the unused C pins should be equally
distributed between the top of the second mux (C12) and
the top of the first mux (C6). If there are an odd number
of cells being used, the top mux should have fewer cells
connected. The unused cell channels should be tied to
the other unused channels on the same mux and then
connected to the battery stack through a 100Ω resistor.
The unused inputs will result in a reading of 0V for those
cells channels. It is also acceptable to connect in the con-
ventional sequence with all unused cell inputs at the top.
isoSPI IBIAS and ICMP Setup
The LTC6804 allows the isoSPI links of each application
to be optimized for power consumption or for noise
immunity. The power and noise immunity of an isoSPI
system is determined by the programmed I
controls the isoSPI signaling currents. Bias current I
range from 100μA to 1mA. Internal circuitry scales up this
bias current to create the isoSPI signal currents equal to
20 • I . A low I reduces the isoSPI power consumption
B B
in the READY and ACTIVE states, while a high I
the amplitude of the differential signal voltage V
the matching termination resistor, R
programmed by the sum of the R
connected between the 2V IBIAS pin and GND as shown in
current, which
B
can
B
increases
B
across
A
. The I current is
M B
and R resistors
B1 B2
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LTC6804-1/LTC6804-2
NEXT HIGHER GROUP
OF 8 CELLS
+
+
+
+
+
+
+
+
NEXT LOWER GROUP
OF 8 CELLS
Figure 40. 8 Cell Connection Scheme
Figure 41. The receiver input threshold is set by the ICMP
voltage that is programmed with the resistor divider created
by the R and R resistors. The receiver threshold will
B1 B2
be half of the voltage present on the ICMP pin.
+
V
LTC6804
C12
S12
C11
S11
C10
S10
C9
S9
C8
S8
C7
S7
C6
S6
C5
S5
C4
S4
C3
S3
C2
S2
C1
S1
C0
–
V
680412 F40
680412fc
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