LTC6802IG-1#PBF Linear Technology, LTC6802IG-1#PBF Datasheet - Page 13

• Manufacturer Part Number: LTC6802IG-1#PBF
• Description: IC MONITOR BATT STACK MC 44-SSOP
• Manufacturer: Linear Technology

Specifications of LTC6802IG-1#PBF

• Function: Battery Monitor
• Battery Type: Lithium-Ion (Li-Ion)
• Voltage - Supply: 4 V ~ 50 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 44-SOP (0.200", 5.30mm Width)
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Figure 3 shows an open connection at the same point in
the cell stack as Figure 2, but this time there is an external
filter network still connected to C3. Depending on the value
of the capacitor remaining on C3, a normal measurement
of B3 and B4 may not give near-zero readings, since the
C3 pin is not truly open. In fact, with a large external ca-
pacitance on C3, the C3 voltage will be charged midway
between C2 and C4 after several cycles of measuring cells
B3 and B4. Thus the measurements for B3 and B4 may
indicate a valid cell voltage when in fact the exact state of
B3 and B4 is unknown.
To reliably detect an open connection, the command
STOWAD is provided. With this command, two 100μA
current sources are connected to the ADC inputs and
turned on during all cell conversions. Referring again to
Figure 3, with the STOWAD command, the C3 pin will be
OPERATION
B4
B3
B4
B3
Figure 3. Open Connection with RC Filtering
C
C
F4
F3
Figure 2. Open Connection
C4
C3
C2
C1
V
–
C4
C3
C2
C1
V
–
MUX
MUX
100μA
100μA
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pulled down by the 100μA current source during the B3
cell measurement AND during the B4 cell measurement.
This will tend to decrease the B3 measurement result and
increase the B4 measurement result relative to the normal
STCVAD command. The biggest change is observed in the
B4 measurement when C3 is open. So, the best method to
detect an open wire at input C3 is to look for an increase
in the measurement of the cell connected between inputs
C3 and C4 (cell B4).
Thus the following algorithm can be used to detect an
open connection to cell pin CN:
(1) Issue a STCVAD command (ADC convert without 100μA
(2) Issue a RDCV command and store all cell measure-
(3) Issue a STOWAD command (ADC convert with 100μA
(4) Issue a RDCV command and store all cell measure-
(5) For each value of N from 1 to 11:
The +200mV threshold is chosen to provide tolerance for
errors in the measurement with the 100μA current source
connected. Even without an open connection there is al-
ways some difference between a cell measured with and
without the 100μA current source because of the IR drop
across the finite resistance of the MUX switches. On the
other hand, with capacitors larger than 0.1μF remaining
on an otherwise open C pin, the 100μA current source
may not be enough to move the open C pin 200mV with
a single STOWAD command. If the STOWAD command
is repeated several times, the large external capacitor will
discharge enough to create a 200mV change in cell read-
ings. To detect an open connection with larger than 0.1μF
capacitance still on the pin, one must repeat step (3) above
a number of times before proceeding to step (4).
The algorithm above determines if the CN pin is open
based on measurements of the N+1 Cell. For example, in
a 12-cell system, the algorithm finds opens on pins C1
current sources).
ments into array CELLA(N).
current sources).
ments into array CELLB(N).
If CELLB(N+1) – CELLA(N+1) ≥ +200mV, then CN is
open, otherwise it is not open.
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