ltc6803g-3 Linear Technology Corporation, ltc6803g-3 Datasheet - Page 33

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

APPLICATIONS INFORMATION
ADDING CALIBRATION AND FULL-STACK
MEASUREMENTS
The general purpose V
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 20 shows a means of selectively pow-
ering an LTC6655-3.3 from the battery stack, under the
control of the GPIO1 output of the LTC6803-1. Since the
operational power of the reference IC would add significant
TEMP
ADC inputs may be used to digi-
LTC6803-1
Figure 20. Providing Measurement of Calibration Reference
V
GPIO1
Figure 21. Using a V
TEMP1
CELL GROUP
CELL GROUP
TOP CELL POTETNTIAL
V
REG
V
–
V
38
34
31
29
WDTB
TEMP1
V
REG
V
1M
+
–
–
1µF
1
TEMP
499k
CZT5551
1M
Si2351DS
10µF
1/2 LT6004
Input for Full-Stack Readings
8
4
thermal loading to the LTC6803 if powered from V
external high voltage NPN pass transistor is used to form
a local 4.4V (V
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 21 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
+
–
3
2
100nF
2N7002K
1
2
3
4
1µF
SHDN
V
GND
GND
LTC6655-3.3
IN
LTC6803-1/LTC6803-3
2
680313 F21
10nF
be
V
V
1
3
OUT_S
OUT_F
below V
GND
GND
31.6k
8
7
6
5
680313 F20
REG
) from the battery stack. The
33
REG
680313f
, an