PRECISION ANALOG FRONT ENDS
TC500
TC500A
TC510
TC514
PIN DESCRIPTION (Cont.)
Pin No
Pin No
Pin No
(TC500/A)
(TC510)
(TC514)
Symbol
Description
10
20
19
CH4–
A0
Negative analog input pin. MUX channel 4
Multiplexer input channel select input LSB. (See A1).
A1
Multiplexer input channel select input MSB.
00 = Channel 1
01 = Channel 2
10 = Channel 3
11 = Channel 4
Phase control input pins: A1, A0 =
GENERAL THEORY OF OPERATION
During Deintegration, S1 connects a reference voltage
(havingapolarityoppositethatofVIN)totheintegratorinput.
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 (tDEINT), as
measured by the precision timer, is directly proportional to
the magnitude of the applied input voltage.
Dual-Slope Conversion Principles (Figure 2)
Actual data conversion is accomplished in two phases:
inputsignalIntegrationandreferencevoltageDeintegration.
The integrator output is initialized to 0V prior to the start
of Integration. During Integration, analog switch S1 con-
nects VIN to the integrator input where it is maintained for a
fixed time period (tINT). The application of VIN causes the
integrator output to depart 0V at a rate determined by the
magnitude of VIN, and a direction determined by the polarity
of VIN. The Deintegration phase is initiated immediately at
A simple mathematical equation relates the Input
Signal, Reference Voltage and Integration time:
the expiration of tINT
.
C
INT
TC510
INTEGRATOR
R
INT
ANALOG
INPUT
–
V
INT
COMPARATOR
–
+
CMPTR OUT
(V
)
IN
+
S1
±
PHASE
CONTROL
SWITCH DRIVER
REF
VOLTAGE
CONTROL
LOGIC
POLARITY
CONTROL
A
B
I/O
MICROCOMPUTER
V
SUPPLY
V
INT
V
V
Ϸ V
IN
IN
FULL SCALE
Ϸ 1/2 V
FULL SCALE
TIMER
ROM
RAM
COUNTER
T
T
INT
DEINT
Figure 2. Basic Dual-Slope Converter
3-24
TELCOM SEMICONDUCTOR, INC.
TELCOM [ TELCOM SEMICONDUCTOR, INC ]
