TC7106 Microchip, TC7106 Datasheet - Page 18

• Manufacturer Part Number: TC7106
• Description: 3-1/2 Digit Analog-to-Digital Converters
• Manufacturer: Microchip

TC7106/A/TC7107/A
10.4
The true differential input and differential reference
make ratiometric reading possible. Typically in a ratio-
metric operation, an unknown resistance is measured,
with respect to a known standard resistance. No accu-
rately defined reference voltage is needed.
The unknown resistance is put in series with a known
standard and a current passed through the pair. The
voltage developed across the unknown is applied to the
input and the voltage across the known resistor is
applied to the reference input. If the unknown equals
the standard, the display will read 1000.
The displayed reading can be determined from the
following expression:
The display will over range for:
FIGURE 10-2:
FIGURE 10-3:
DS21455B-page 18
R
UNKNOWN
R
160kΩ
1N4148
Sensor
STANDARD
Displayed Reading
Ratiometric Resistance
Measurements
50kΩ
R
UNKNOWN
R
2
(
300kΩ
50kΩ
R
≥ 2 x R
1
LOW PARTS COUNT
RATIOMETRIC
RESISTANCE
MEASUREMENT
TEMPERATURE SENSOR
V
V
V
Analog
Common
V
IN
REF
IN
REF
TC7106A
+
300kΩ
-
)
+
-
=
STANDARD
V+
RUnknown
-------------------------------x1000
RS
V
V
V
V
Common
IN
IN
REF
REF
V+
tan
-
+
+
-
+
TC7106A
dard
V
FS
LCD Display
= 2V
9V
V-
FIGURE 10-4:
FIGURE 10-5:
0.7%/°C
TC7106A
PTC
5.6kΩ
1N914
To Pin 1
R
40
39
38
37
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
3
20kΩ
20kΩ
0.22µF
0.47µF
To Display
R
R
0.1µF
1
2
COEFFICIENT RESISTOR
TEMPERATURE SENSOR
TC7106A, USING THE
INTERNAL REFERENCE:
200mV FULL SCALE, 3
READINGS-PER-SECOND
(RPS)
POSITIVE TEMPERATURE
©
To Backplane
100kΩ
100pF
2002 Microchip Technology Inc.
160kΩ
Set V
1kΩ
47kΩ
REF
0.01µF
V
V
V
V
Common
V+
IN
IN
REF
REF
= 100mV
TC7106A
-
+
22kΩ
1MΩ
+
-
+
+
–
9V
9V
V-
+
–
IN