TC818A View Datasheet(PDF) - Microchip Technology
Part Name
Description
Manufacturer
TC818A Datasheet PDF : 24 Pages
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TC818A
FIGURE 3-2:
RATIOMETRIC RESISTANCE MEASUREMENT FUNCTIONAL DIAGRAM
R5/1638500Ω
39
S29
VSS 57
R4/163850Ω 38
R3/16385Ω 37
R2/1638.5Ω 36
R1/163.85Ω
35
S30
S31
S32
S33
÷10k ÷1k ÷100 ÷10 ÷1
Ohms
VA Ω • HIΩ
Low Ohms
Ω • LO
VCC
10kΩ
~1.5kΩ
~1.5kΩ
S24 S25 S26 S27 S28
Voltage
Reference
R8
220Ω
(PTC)
33
CREF
0.1µF 32
31
R6/100kΩ
S23 DE • Ω
+
≈ VCC -2.8V
S20
DE S19
DE + Ω –
S18
DE
S21 DE • Ω
DE
Buffer
VCC -2.6V
TC818A
R7/100kΩ 50
S12
RX Unknown
V•
1
1
S13
INT • ( Ω + DC)
S35
S37 Ω Ω
Integrator
Comparator
S36
Ω
S34
Ω
9V +
VCC
28
R18
24kΩ
REFHI
34
5kΩ
29
Analog
Common
RΩBUF 54 55
49
RVIBUF
150kΩ
220kΩ
CAZ
47
0.1µF
CINT
0.1µF
FIGURE 3-3:
RS
163.85kΩ
Unknown
RESISTANCE MEASUREMENT ACCURACY SET BY EXTERNAL
STANDARD RESISTOR
VA =
0.64V for Ohms
0.32V for LO Ohms
Example: 200kΩ Full Scale Measurement
(a )
VR
=
------------1---6----3---.--8---5----k---Ω---------------
163.85 + 220 + RX
x
0.64
+
CREF
VR
100kΩ
(b)
VX
=
----------------------------R----X------------------------------
163.85kΩ + 220Ω + RX
x0.64
220Ω
VX
RX To Analog Buffer
(c) “Ramp Up Voltage” = “Ramp Down Voltage”
.
..
-----V----X-------
(RICI)
xT
I
=
-----V----X------- T
(RICI)
D
E
Where:
RI = Integrating Resistor, TI = Integrate Time
CI = Integrating Capacitor, TDE = De-integrate Time
(d)
RX
=
163.85
(TDE)
TI
Independent of RI, CI or Internal Voltage Reference
© 2002 Microchip Technology Inc.
DS21475B-page 9
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