TC7126 TelCom, TC7126 Datasheet - Page 5

• Manufacturer Part Number: TC7126
• Description: 3-1/2 DIGIT ANALOG-TO-DIGITAL CONVERTERS
• Manufacturer: TelCom

GENERAL THEORY OF OPERATION
Dual-Slope Conversion Principles
digital converter. An understanding of the dual-slope con-
version technique will aid in following detailed TC7126A
operational theory.
cycle has two distinct phases:
fixed time period (t
An opposite polarity constant reference voltage is then
integrated until the integrator output voltage returns to
zero. The reference integration time is directly proportional
to the input signal (t
sion requires the integrator output to "ramp-up" and "ramp-
down."
reference voltage, and integration time:
3-1/2 DIGIT
ANALOG-TO-DIGITAL CONVERTERS
PIN DESCRIPTION (Cont.)
40-Pin PDIP
Pin Number
Normal
(All Pin Designations Refer to the 40-Pin DIP)
The TC7126A is a dual-slope, integrating analog-to-
The conventional dual-slope converter measurement
(1) Input signal integration
(2) Reference voltage integration (deintegration)
The input signal being converted is integrated for a
In a simple dual-slope converter, a complete conver-
A simple mathematical equation relates the input signal,
TELCOM SEMICONDUCTOR, INC.
34
35
36
37
38
40
RC
1
(Reverse)
SI
t
(7)
(6)
(5)
(4)
(3)
(2)
(1)
0
SI
RI
), measured by counting clock pulses.
).
V
IN
(t) dt =
Name
V
OSC
OSC
OSC
TEST
C
V
V
RC
R
REF
+
REF
–
+
REF
t
RI
3
2
1
,
Description
A 0.1 F capacitor is used in most applications. If a large common-mode voltage
exists (for example, the V
used, a 1 F capacitor is recommended and will hold the roll-over error to 0.5
count.
See pin 36.
The analog input required to generate a full-scale output (1999 counts). Place 100
mV between pins 35 and 36 for 199.9 mV full scale. Place 1V between pins 35
and 36 for 2V full scale. See paragraph on reference voltage.
Lamp test. When pulled HIGH (to V
display should read –1888. It may also be used as a negative supply for exter-
nally-generated decimal points. See paragraph under test for additional informa-
tion.
See pin 40.
See pin 40.
Pins 40, 39 and 38 make up the oscillator section. For a 48 kHz clock (3 readings
39per second), connect pin 40 to the junction of a 180 k resistor and a 50 pF
capacitor. The 180 k resistor is tied to pin 39 and the 50 pF capacitor is tied to
pin 38.
where:
ANALOG
VOLTAGE
INTEGRATE
SIGNAL
V
t
t
INPUT
SI
RI
R
REF
IN
SIGNAL
= Reference voltage
= Signal integration time (fixed)
= Reference voltage integration time (variable).
FIXED
–
TIME
pin is not at analog common), and a 200 mV scale is
Figure 1. Basic Dual-Slope Converter
POLARITY CONTROL
VARIABLE
REFERENCE
INTEGRATE
TIME
+
), all segments will be turned ON and the
DISPLAY
INTEGRATOR
SWITCH
DRIVER
–
+
V IN
V IN
PHASE
CONTROL
V FULL SCALE
1.2 V FULL SCALE
–
+
COMPARATOR
CONTROL
LOGIC
COUNTER
TC7126A
TC7126
CLOCK
3-221
1
2
3
4
5
6
7
8