TMPSNSRD-TCPL1 Microchip Technology, TMPSNSRD-TCPL1 Datasheet - Page 14

• Manufacturer Part Number: TMPSNSRD-TCPL1
• Description: BOARD RTD REFERENCE DESIGN
• Manufacturer: Microchip Technology

Specifications of TMPSNSRD-TCPL1

• Sensor Type: Temperature, Thermocouple
• Embedded: No
• Utilized Ic / Part: MCP3421, MCP9804
• Processor To Be Evaluated: MCP9804, MCP3421
• Interface Type: USB
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Supply: -
• Interface: -
• Sensitivity: -
• Sensing Range: -
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

The table below shows a comparison of the gain between the
circuits (a and b) in Figure 1-1 when using the same Digital
Potentiometer (10 kΩ, 7-bit). What you also see is that
when R
and 3. While when the simplifi ed circuit is used (effectively
having R
and >127. Therefore the capability for fi ner calibration of
the circuit is capable with the generic circuit, albeit with a
narrower range.
Some devices have an even number of step resistors (R
in the R
the simplifi ed circuit, devices with an even number of R
resistors have a mid-scale wiper value that is unity gain.
14
Amplifier Gain vs. Wiper Code and R
Note 1: Gain = ( (R
Programmable Gain Using Digital Potentiometers
2: Uses R
3: Theoretical calculations. At full scale in the simplified circuit a divide by 0 error results.
Taps
# of
129
Signal Chain Design Guide
1
AB
1
= R
= R
string, while others have an odd number. In
1
= R
2
AB
2
= 10 kΩ, the circuit’s gain range is between 1
2
= 0Ω) the circuit’s gain range is between ~0
/ # of Resistors) * Wiper Code ) /( ( (# of Resistors - Wiper Code) / # of Resistors) * R
= 10 kΩ.
Resistors
# of
128
Wiper
Code
124
125
126
127
128
62
63
64
65
66
0
1
2
3
4
.
.
.
.
.
.
W
Simplified Circuit
S
Divide Error
127.000000
S
31.000000
41.666667
63.000000
0.007874
0.015873
0.024000
0.032258
0.939394
0.969231
1.000000
1.031746
1.064516
)
0.0
.
.
.
.
.
.
(3)
For devices with an odd number of R
scale wiper value that is near unity gain. The MCP4261 is an
example of a device that has an even number of R
in the R
device that has an odd number of R
string.
For devices with an odd number of R
string to be able to have an exact unity gain, the device
would need to be used in the generic circuit confi guration
(Figure 1-1), and the components would need to be selected
so R
(1)
10 kΩ Gain
1
+ R
AB
AW
string, while the MCP4011 is an example of a
AB
)
could equal R
Generic Circuit
1.000000
1.007843
1.015748
1.023715
1.031746
1.639175
1.652850
1.666667
1.680628
1.694737
2.878788
2.908397
2.938462
2.968992
3.000000
.
.
.
.
.
.
2
(1, 2)
+ R
BW
.
S
S
S
resistors in the R
resistors have a mid-
resistors in the R
Comment
Zero Scale
Mid Scale
Full Scale
.
.
.
.
.
.
S
resistors
AB
AB