LTC6803 View Datasheet(PDF) - Linear Technology
Part Name
Description
MFG CO.
'LTC6803' PDF : 40 Pages View PDF
LTC6803-1/LTC6803-3
APPLICATIONS INFORMATION
For sensors that require higher drive currents, a buffer
op amp may be used as shown in Figure 17. Power for
the sensor is actually sourced indirectly from the VREG
pin in this case. Probe loads up to about 1mA maximum
are supported in this configuration. Since VREF is shut-
down during the LTC6803 idle and shutdown modes, the
thermistor drive is also shut off and thus power dissipation
minimized. Since VREG remains always on, the buffer op
amp (LT6000 shown) is selected for its ultralow power
consumption (12µA).
Expanding Probe Count
As shown Figure 18, a dual 4:1 multiplexer is used to ex-
pand the general purpose VTEMP1 and VTEMP2 ADC inputs
to accept 8 different probe signals. The channel is selected
by setting the general purpose digital outputs GPIO1 and
GPIO2 and the resultant signals are buffered by sections
of the LT6004 micropower dual operational amplifier. The
probe excitation circuitry will vary with probe type and is
not shown here.
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 VTEMP input(s). The hottest
diode will therefore dominate the readout from the VTEMP
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 19 shows the basic concept. In any of the sensor
configurations shown, a full-scale cold readout would be
an indication of a failed open-sensor connection to the
LTC6803.
LTC6803-1
VREG
VREF
VTEMP2
VTEMP1
NC
V–
100k
100k
1µF
1µF
100k
100k
NTC
NTC
680313 F16
Figure 16. Driving Thermistors Directly from VREF
LTC6803-1
VREG
VREF
VTEMP2
VTEMP1
NC
V–
+
LT6000
–
10k
10k
10k
10k
NTC
NTC
680313 F17
Figure 17. Buffering VREF for Higher Current Sensors
65
4
8
1/2 LT6004
7
1 Y0
2 Y2
VCC
X2
16
15
3Y
X1 14
4
5
Y3 74HC4052 X
Y1
X0
13
12
6 INH
X3 11
7
8
VEE
GND
A 10
B9
CPO2
GPO1
VREG
VTEMP2
1/2 LT6004 8 3
VTEMP1
1
2
4
1µF
V–
PROBE8
PROBE7
PROBE6
PROBE5
PROBE4
PROBE3
PROBE2
PROBE1
680313 F18
Figure 18. Expanding Sensor Count with Multiplexing
LTC6803-1
VREG
VREF
VTEMP2
VTEMP1
NC
V–
200k
200k
680313 F19
Figure 19. Using Diode Sensors as Hot Spot Detectors
680313f
32
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