tc7129 Microchip Technology Inc., tc7129 Datasheet - Page 8

• Manufacturer Part Number: tc7129
• Description: 4-1/2 Digit Analog-to-digital Converters With On-chip Lcd Drivers
• Manufacturer: Microchip Technology Inc.

Figure 3-1:
3.3
The charge stored in the integrating capacitor during
the integrate phase is directly proportional to the input
voltage. The primary selection criterion for C
choose a value that gives the highest voltage swing
while remaining within the high-linearity portion of the
integrator output range. An integrator swing of 2V is the
recommended value. The capacitor value can be
calculated using the following equation:
EQUATION 3-1:
Using the values derived above (assuming 60 Hz
operation), the equation becomes:
EQUATION 3-2:
DS21459D-page 8
TC7129
Integrating Capacitor (C
C
Where t
INT
=
16.7 msec x 13.3 A
C
INT
20
21
INT
is the integration time.
19
22
Standard Circuit.
=
2V
t
18
23
INT
V
SWING
17
24
x I
+
INT
9V
16
25
15
26
= 0.1 A
10 k
R
BIAS
C
0.1 µF
INT
14
27
INT
)
13
28
Display Drive Outputs
150 kΩ
Low Battery
R
INT
TC7129
INT
12
29
C
1 µF
is to
REF
30
11
+
10
31
–
32
9
C
V
0.1
µF
Continuity
IF
IN
The capacitor should have low dielectric absorption to
ensure good integration linearity. Polypropylene and
Teflon
measurement of the dielectric absorption is to connect
the
connecting:
Pin-to-Pin:
A reading between 10,000 and 9998 is acceptable;
anything lower indicates unacceptably high dielectric
absorption.
3.4
The reference capacitor stores the reference voltage
during several phases of the measurement cycle. Low
leakage is the primary selection criterion for this com-
ponent. The value must be high enough to offset the
effect of stray capacitance at the capacitor terminals. A
value of at least 1 F is recommended.
33
8
+
100 kΩ
R
34
7
IF
reference capacitor
®
35
6
Reference Capacitor (C
capacitors are usually suitable. A good
R
20
kΩ
REF
36
5
20
30
37
4
D
REF
38
3
33 (C
32 (C
39
2
© 2006 Microchip Technology Inc.
REF
REF
40
1
0.1 µF
C
RF
across
330 kΩ
+ to IN HI)
– to IN LO)
10 pF
R
5 pF
120
kHz
O
V+
V+
the
Crystal
REF
C
C
O1
O2
inputs
)
by