PRECISION ANALOG FRONT ENDS
TC500
TC500A
TC510
TC514
PIN DESCRIPTION
(Cont.)
Pin No
(TC500/A)
Pin No
(TC510)
Pin No
(TC514)
10
20
19
Symbol
CH4
–
A0
A1
Description
Negative analog input pin. MUX channel 4
Multiplexer input channel select input LSB. (See A1).
Multiplexer input channel select input MSB.
00 = Channel 1
01 = Channel 2
Phase control input pins: A1, A0 =
10 = Channel 3
11 = Channel 4
GENERAL THEORY OF OPERATION
Dual-Slope Conversion Principles
(Figure 2)
Actual data conversion is accomplished in two phases:
input signal Integration and reference voltage Deintegration.
The integrator output is initialized to 0V prior to the start
of Integration. During Integration, analog switch S1 con-
nects V
IN
to the integrator input where it is maintained for a
fixed time period (t
INT
). The application of V
IN
causes the
integrator output to depart 0V at a rate determined by the
magnitude
of V
IN
, and a direction determined by the
polarity
of V
IN
. The Deintegration phase is initiated immediately at
the expiration of t
INT
.
During Deintegration, S1 connects a reference voltage
(having a polarity opposite that of V
IN
) to the integrator input.
At the same time, an external precision timer is started. The
Deintegration phase is maintained until the comparator
output changes state, indicating the integrator has returned
to its starting point of 0V. When this occurs, the precision
timer is stopped. The Deintegration time period (t
DEINT
), as
measured by the precision timer, is directly proportional to
the magnitude of the applied input voltage.
A simple mathematical equation relates the Input
Signal, Reference Voltage and Integration time:
CINT
RINT
INTEGRATOR
–
+
VINT
–
+
PHASE
CONTROL
TC510
COMPARATOR
CMPTR OUT
ANALOG
INPUT
(VIN)
±
REF
VOLTAGE
S1
SWITCH DRIVER
POLARITY
CONTROL
CONTROL
LOGIC
A
INTEGRATOR
OUTPUT
B
I/O
VIN
VIN
TINT
TDEINT
VFULL SCALE
1/2 VFULL SCALE
VSUPPLY
VINT
MICROCOMPUTER
ROM
RAM
TIMER
COUNTER
Figure 2. Basic Dual-Slope Converter
3-24
TELCOM SEMICONDUCTOR, INC.
TELCOM [ TELCOM SEMICONDUCTOR, INC ]
