Datasheet

LTC6802-1
31
68021fa
APPLICATIONS INFORMATION
in this case. Probe loads up to about 1mA maximum are
supported in this configuration. Since V
REF
is shutdown
during the LTC6802-1 idle and shutdown modes, the
thermistor drive is also shut off and thus power dissipa-
tion minimized. Since V
REG
remains always on, the buffer
op amp (LT6000 shown) is selected for its ultralow power
consumption (10µA).
Expanding Probe Count
The LTC6802-1 provides general purpose I/O pins, GPIO1
and GPIO2, that may be used to control multiplexing of
several temperature probes. Using just one of the GPIO
pins, the sensor count can double to four as shown in
Figure 16. Using both GPIO pins, up to eight sensor inputs
can be supported.
Using Diodes to Monitor Temperatures in Multiple
Locations
Another method of multiple sensor support is possible
without the use of any GPIO pins. If the sensors are PN
diodes and several used in parallel, then the hottest diode
will produce the lowest forward voltage and effectively
establish the input signal to the V
TEMP
input(s). The hottest
Figure 17. Using Diode Sensors as Hot-Spot Detectors
Figure 16. Expanding Sensor Count with Multiplexing
LTC6802-1
100k
NTC
100k
NTC
100k
NTC
100k
NTC
1µF
100k
100k
100k
SN74LVC1G3157
OR SIMILAR DEVICE
GPIO1
V
REG
V
REF
V
TEMP2
V
TEMP1
NC
V
−
68021 F16
200k
200k
V
REG
V
REF
V
TEMP2
V
TEMP1
NC
V
−
LTC6802-1
68021 F17
diode will therefore dominate the readout from the V
TEMP
inputs that the diodes are connected to. In this scenario,
the specific location or distribution of heat is not known,
but such information may not be important in practice.
Figure 17 shows the basic concept.
In any of the sensor configurations shown, a full-scale
cold readout would be an indication of a failed-open sen-
sor connection to the LTC6802-1.
ADDING CALIBRATION AND
FULL-STACK MEASUREMENTS
By adding multiplexing hardware, additional signals can
be digitized by the CELL1 ADC channel. One useful signal
to provide is a high-accuracy voltage reference, such as
from an LT1461A-4. By periodic readings of this signal,
host software can provide correction of the LTC6802-1
readings to improve the accuracy over that of the internal
LTC6802-1 reference, and/or validate ADC operation. An-
other useful signal is a measure of the total stack potential.
This provides a redundant operational measurement of the
cells in the event of a malfunction in the normal acquisi-
tion process, or as a faster means of monitoring the entire