TC820 TelCom Semiconductor, TC820 Datasheet - Page 8

• Manufacturer Part Number: TC820
• Description: 3-3/4 DIGIT A/D CONVERTER WITH FREQUENCY COUNTER AND LOGIC PROBE
• Manufacturer: TelCom Semiconductor

TC820
GENERAL THEORY OF OPERATION
Dual-Slope Conversion Principles
principle of dual-slope integration. An understanding of the
dual-slope conversion technique will aid the user in follow-
ing the detailed TC820 theory of operation following this
section. A conventional dual-slope converter measurement
cycle has two distinct phases:
converted is integrated from zero for a fixed time period
(t
reference voltage of the opposite polarity is then integrated
until the integrator output voltage returns to zero. The
reference integration (deintegration) time (T
directly proportional to the unknown input voltage (V
sion requires the integrator output to "ramp-up" from zero
and "ramp-down" back to zero. A simple mathematical
equation relates the input signal, reference voltage, and
integration time:
3-156
INT
The TC820 analog-to-digital converter operates on the
(1) Input Signal Integration
(2) Reference Voltage Integration (Deintegration)
Referring to Figure 2, the unknown input signal to be
In a simple dual-slope converter, a complete conver-
), measured by counting clock pulses. A constant
LOGIC
FREQ
GND
V IN
V DD
DGND
V DD
SWITCH
S1b
S1c
S1e
S1a
S1d
S1a
TO
S2
CHANGE
DP3
RANGE
100k
NO DP
0.01 F
TO SWITCH
S2
DP2
DP1
V DD
COM
24
18
33
32
16
19
20
21
FREQ/
VOLTS
LOGIC
V
V
DGND
RANGE/FREQ
DP0/LO
DP1/HI
IN
IN
+
–
LOGIC HIGH
LOGIC LOW
37
OSC1
DEINT
40kHz
22M
1
Figure 1. Typical Operating Circuit
2
) is then
OSC2 OSC3 V BUFF C AZ
3
4
IN
38
OVERRANGE
470
k
).
5
6
NC
39
7
TC820
8
34
100
k
9
INTEGRATE
PKHOLD
10 11 12 13 14 15
ANALOG
VOLTAGE
SIGNAL
INPUT
SIGNAL
35
0.47
FIXED
REF
F
TIME
V INT
LOW BATT
36
0.2
F
C
REF C
+
Figure 2. Basic Dual-Slope Converter
NC
PK HOLD
BUZ OUT
3-3/4 A/D CONVERTER WITH
28
POLARITY CONTROL
17
0.1
R
BUZ IN
F
V
V
COM
V SS
–
REF
REF
REF
V DD
+
–
VARIABLE
REFERENCE
INTEGRATE
TIME
29
DISPLAY
INTEGRATOR
SWITCH
DRIVER
FREQUENCY COUNTER
TELCOM SEMICONDUCTOR, INC.
30
31
27
40
26
22
23
25
NOTE:
Pin numbers are for
40-pin package.
–
+
DGND
+
–
V DD
V IN
V IN
C
9V
DGND
AND LOGIC PROBE
PHASE
CONTROL
22k
2k
V REF = 200mV
PIEZO
BUZZER
=
=
+
1.2 V FULL SCALE
V FULL SCALE
1 F
–
+
COMPARATOR
V DD
V DD
V DD
CONTROL
LOGIC
COUNTER
CLOCK