Datasheet
LTC6803-2/LTC6803-4
33
680324fa
APPLICATIONS INFORMATION
ADDING CALIBRATION AND FULL-STACK
MEASUREMENTS
The general purpose V
TEMP
ADC inputs may be used to digi-
tize any signals from 0V to 4V with accuracy corresponding
closely with that of the cell 1 ADC input. One useful signal
to provide is a high accuracy voltage reference, such as
3.300V from an LTC6655-3.3. From periodic readings of
this signal, the host software can provide correction of
the LTC6803 readings to improve the accuracy over that
of the internal LTC6803 reference and/or validate ADC
operation. Figure 18 shows a means of selectively pow-
ering an LTC6655-3.3 from the battery stack, under the
control of the GPIO1 output of the LTC6803-2. Since the
operational power of the reference IC would add significant
thermal loading to the LTC6803 if powered from V
REG
, an
external high voltage NPN pass transistor is used to form
a local 4.4V (V
be
below V
REG
) from the battery stack. The
GPIO1 signal controls a PMOS FET switch to activate the
reference when calibration is to be performed. Since GPIO
signals default to logic high in shutdown, the reference
will automatically turn off during idle periods.
Another useful signal is a measure of the total stack poten-
tial. This provides a redundant operational measurement
of the cells in the event of a malfunction in the normal
acquisition process, or as a faster means of monitoring
the entire stack potential. Figure 19 shows how a resis-
tive divider is used to derive a scaled representation of a
full cell group potential. A MOSFET is used to disconnect
Figure 16. Expanding Sensor Count with Multiplexing
Figure 17. Using Diode Sensors as Hot Spot Detectors
6
4 8
7
1
8
3
2
1µF
680324 F16
4
1/2 LT6004
1/2 LT6004
+
–
+
–
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
Y0
Y2
Y
Y3
Y1
INH
V
EE
GND
PROBE8
PROBE7
PROBE6
PROBE5
PROBE4
PROBE3
PROBE2
PROBE1
CPO2
GPO1
V
REG
V
TEMP2
V
TEMP1
V
–
V
CC
X2
X1
X
X0
X3
A
B
74HC4052
5
V
REG
V
REF
V
TEMP2
V
TEMP1
NC
V
–
LTC6803-4
200k
680324 F17
200k
GPIO1
35
V
REG
31
V
TEMP1
28
V
–
26
1M
TOP CELL POTENTIAL
Si2351DS 100nF
LTC6803-2
SHDN
V
IN
GND
GND
GND
V
OUT_F
V
OUT_S
GND
1
2
3
4
8
7
6
5
1µF 10µF
680324 F18
LTC6655-3.3
CZT5551
Figure 18. Providing Measurement of Calibration Reference