TC7136 View Datasheet(PDF) - TelCom Semiconductor Inc => Microchip
Part Name
Description
Manufacturer
TC7136 Datasheet PDF : 12 Pages
| |||
LOW POWER, 3-1/2 DIGIT
ANALOG-TO-DIGITAL CONVERTERS
1
TC7136
TC7136A
TC7136/A PIN DESCRIPTION (Cont.)
Pin No.
2
40-Pin PDIP
Normal (Reverse) Name
Description
33
(8)
C–REF
See pin 34.
34
(7)
C+REF
A 0.1 µF capacitor is used in most applications. If a large common-mode
voltage exists (for example, the VIN– pin is not at analog common), and a 200
mV scale is used, a 1 µF capacitor is recommended and will hold the roll-over
error to 0.5 count.
35
(6)
V–REF
See pin 36.
3
(5)
V–REF
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.
36
(4)
TEST
Lamp test. When pulled HIGH (to V+) all segments will be turned ON and the
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.
37
(3)
OSC3
See pin 40.
4
38
(2)
OSC2
See pin 40.
39
(1)
OSC1
Pins 40, 39 and 38 make up the oscillator section. For a 48 kHz clock (3 readings per
second) connect pin 40 to the junction of a 180 kΩ resistor and a 50 pF capacitor. The
180 kΩ resistor is tied to pin 39 and the 50 pF capacitor is tied to pin 38.
GENERAL THEORY OF OPERATION
(All Pin designations refer to 40-Pin Dip)
Dual-Slope Conversion Principles
The TC7136/A is a dual-slope, integrating analog-to-
digital converter. An understanding of the dual-slope con-
version technique will aid in following detailed TC7136/A
operational theory.
The conventional dual-slope converter measurement
cycle has two distinct phases:
(1) Input signal integration
(2) Reference voltage integration (deintegration)
The input signal being converted is integrated for a fixed
time period (tSI), measured by counting clock pulses. An
opposite polarity constant reference voltage is then inte-
grated until the integrator output voltage returns to zero. The
reference integration time is directly proportional to the input
signal (tRI).
In a simple dual-slope converter, a complete conversion
requires the integrator output to "ramp-up" and "ramp-
down."
A simple mathematical equation relates the input signal,
reference voltage, and integration time:
∫1
RC
tSI
0
VIN(t) dt =
VR tRI
RC
,
TELCOM SEMICONDUCTOR, INC.
ANALOG
INPUT
SIGNAL
CINT
INTEGRATOR
–
+
COMPARATOR
–
+
5
REF
VOLTAGE
SWITCH
DRIVER
PHASE
CONTROL
CONTROL
LOGIC
POLARITY CONTROL
CLOCK
6
DISPLAY
COUNTER
VIN Ϸ VFULL SCALE
VIN Ϸ 1.2 VFULL SCALE
FIXED
SIGNAL
INTEGRATE
TIME
VARIABLE
REFERENCE
INTEGRATE
TIME
Figure 1. Basic Dual-Slope Converter
where:
VR = Reference voltage
tSI = Signal integration time (fixed)
tRI = Reference voltage integration time (variable).
For a constant VIN:
[ ]tRI
VIN = VR tSI .
3-251
7
8
Share Link: 