ltc6803g-3 Linear Technology Corporation, ltc6803g-3 Datasheet - Page 28

• Manufacturer Part Number: ltc6803g-3
• Description: Ltc6803-1/ltc6803-3 - Multicell Battery Stack Monitor
• Manufacturer: Linear Technology Corporation

LTC6803-1/LTC6803-3
APPLICATIONS INFORMATION
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 11, with the STOWAD command, the C3 pin will be
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
28
B4
B3
+
+
+
+
+
B4
B3
+
+
+
+
+
Figure 11. Open Connection with RC Filtering
C
C
F4
F3
Figure 10. Open Connection
21
23
25
27
29
C4
C3
C2
C1
V
–
21
23
25
27
29
MUX
C4
C3
C2
C1
V
–
MUX
100µA
LTC6803-1
100µA
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LTC6803-1
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in the value of battery connected between inputs C3 and
C4 (battery B4).
The following algorithm can be used to detect an open
connection to cell pin Cn:
1. Issue a STOWAD command (with 100µA sources
2. Issue a RDCV command and store all cell measurements
3. Issue the 2nd STOWAD command (with 100µA sources
4. Issue the 2nd RDCV command and store all cell mea-
5. For battery cells, if CELLA(1) < 0 or CELLB(1) < 0, V
The 200mV threshold is chosen to provide tolerance for
measurement errors. For a system with the capacitor con-
nected to Cn larger than 0.5µF , repeating step 3 several
times will discharge the external capacitor enough to meet
the criteria.
If the top C pin is open yet V
best way to detect an open connection to the top C pin
is by comparing the sum of all cell measurements using
the STCVAD command to an auxiliary measurement of
the sum of all the cells, using a method similar to that
shown in Figure 21. A significantly lower result for the
sum of all 12 cells suggests an open connection to the
top C pin, provided it was already determined that no
other C pin is open.
USING THE S PINS AS DIGITAL OUTPUTS OR
GATE DRIVERS
The S outputs include an internal pull-up PMOS. Therefore
the S pins will behave as a digital output when loaded with
a high impedance, e.g., the gate of an external MOSFET.
For applications requiring high battery discharge currents,
connect a discrete PMOS switch device and suitable
connected).
into array CELLA(n).
connected).
surements into array CELLB(n).
must be open.
If CELLA(12) < 0 or CELLB(12) < 0, C12 must be open.
For n = 2 to 11, if CELLB(n+1) – CELLA(n+1) > 200mV,
or CELLB(n+1) reaches the full scale of 5.375V, then
Cn is open.
+
is still connected, then the
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–