LTC6804-1/LTC6804-2
29
680412fc
For more information www.linear.com/LTC6804-1
operaTion
The CLRAUX command clears auxiliary register group
A and B. All bytes in these registers are set to 0xFF by
CLRAUX command.
The CLRSTAT command clears status register group A and
B except the REVCODE and RSVD bits in status register
group B. A read back of REVCODE will return the revision
code of the part. All OV flags, UV flags, MUXFAIL bit, and
THSD bit in status register group B are set to 1 by CLR
-
STAT command. The THSD bit is set to 0 after RDSTATB
command. The registers storing SOC, ITMP
, V
A and VD
are all set to 0xFF by CLRSTAT command.
Open-Wire Check (ADOW Command)
The ADOW command is used to check for any open wires
between the ADCs in the LTC6804 and the external cells.
This command performs ADC conversions on the C pin
inputs identically to the ADCV command, except two
internal current sources sink or source current into the
two C pins while they are being measured. The pull-up
(PUP) bit of the ADOW command determines whether the
current sources are sinking or sourcing 100µA.
The following simple algorithm can be used to check for
an open wire on any of the 13 C pins (see Figure 9):
1) Run the 12-cell command ADOW with PUP = 1 at least
twice. Read the cell voltages for cells 1 through 12 once
at the end and store them in array CELL
PU(n)
.
2) Run the 12-cell command ADOW with PUP = 0 at least
twice. Read the cell voltages for cells 1 through 12 once
at the end and store them in array CELL
PD(n)
.
3) Take the difference between the pull-up and pull-down
measurements made in above steps for cells 2-12:
CELL
∆(n)
= CELL
PU(n)
– CELL
PD(n)
.
4) For all values of n from 1 to 11: If CELL
∆(n+1)
< –400mV,
then C(n) is open. If the CELL
PU(1)
= 0.0000, then C(0)
is open. If the CELL
PD(12)
= 0.0000, then C(12) is open.
The above algorithm detects open wires using normal mode
conversions with as much as 10nF of capacitance remaining
on the LTC6804 side of the open wire. However, if more
external capacitance is on the open C pin, then the length
of time that the open wire conversions are ran in steps 1
and 2 must be increased to give the 100µA current sources
time to create a large enough difference for the algorithm
to detect an open connection. This can be accomplished
by running more than two ADOW commands in steps 1
and 2, or by using filtered mode conversions instead of
normal mode conversions. Use Table 11 to determine how
many conversions are necessary:
Table 11
Number of ADOW Commands Required in
Steps 1 and 2
EXTERNAL C PIN
CAPACIT
ANCE NORMAL MODE FILTERED MODE
≤10nF 2 2
100nF 10 2
1µF 100 2
C 1+ROUNDUP(C/10nF) 2
2
+
+
+
+
+
+
+
V
+
V
–
100µA
100µA
PUP = 1
C12
PUP = 0
V
+
V
+
V
–
ADC2
LTC6804
4
C11
6
C10
8
C9
6-CELL
MUX
10
C8
12
14
C7
C6
C6
1
16
+
+
+
+
+
V
+
V
–
100µA
100µA
PUP = 1
C5
PUP = 0
V
+
V
–
V
–
680412 F09
ADC1
18
C4
20
C3
22
C2
6-CELL
MUX
24
C1
26
30
31
C0
Figure 9. Open-Wire Detection Circuitry
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