3-1/2 DIGIT A/D CONVERTERS
TC7106
TC7106A
TC7107
TC7107A
C
+
+
INPUT
BUFFER
I
V
V
+
V
R
+
V
–
+
–
I
+
V
–
+
+
REF
6.8V
ZENER
V
V
I
6.8kΩ
IN
–
V
INTEGRATOR
TC7106A
TC7107A
REF
20kΩ
T
I
I
V
=
V
– V
Z
+
I
I
[
CM
IN
[
V
CM
R C
V
TC7106A
TC7107A
I
I
REF
TC04
Where:
4000
fOSC
T
INTEGRATION TIME
=
=
=
–
V
1.2V
REF
REF
C
R
INTEGRATION CAPACITOR
= INTEGRATION RESISTOR
I
I
COMMON
(b)
(a)
Figure 7. External Reference
Figure 9. Common-Mode Voltage Reduces Available Integrator
Swing. (VCOM ≠ VIN)
DEVICE PIN FUNCTIONAL DESCRIPTION
full-scale swing. The integrator output will swing within 0.3V
of V+ or V– without increasing linearity errors.
Differential Signal Inputs
(V+IN (Pin 31), V–IN (Pin 30))
The TC7106A/7017A is designed with true differential
inputs and accepts input signals within the input stage
common mode voltage range (VCM). The typical range is V+
–1.0 to V– +1 V. Common-mode voltages are removed from
the system when the TC7106A/TC7107A operates from a
battery or floating power source (isolated from measured
system) and VI–N is connected to analog common (VCOM):
See Figure 8.
Differential Refe–rence
(VR+EF (Pin 36), VREF (Pin 35))
The reference voltage can be generated anywhere
within the V+ to V– power supply range.
To prevent rollover errors from being induced by large
common-mode voltages, CREF should be large compared to
stray node capacitance.
The TC7106A/TC7107A circuits have a significantly
lower analog common temperature coefficient. This gives a
very stable voltage suitable for use as a reference. The
temperature coefficient of analog common is 20ppm/°C
typically.
In systems where common-mode voltages exist, the
86dB common-mode rejection ratio minimizes error. Com-
mon-mode voltages do, however, affect the integrator out-
put level. Integrator output saturation must be prevented. A
worst-case condition exists if a large positive VCM exists in
conjunctionwithafull-scalenegativedifferentialsignal. The
negative signal drives the integrator output positive along
with VCM (Figure 9). For such applications the integrator
output swing can be reduced below the recommended 2.0V
SEGMENT
DRIVE
LCD DISPLAY
MEASURED
SYSTEM
V
+
C
V
POL BP
BUF
AZ
INT
OSC
1
V IN
+
V
–
OSC
OSC
3
2
V IN
TC7106A
–
V
GND
ANALOG
COMMON REF REF
–
+
+
–
V
V
V
V
+
–
V
V
GND
POWER
SOURCE
+
9V
Figure 8. Common-Mode Voltage Removed in Battery Operation with VI–N = Analog Common
3-194
TELCOM SEMICONDUCTOR, INC.
TELCOM [ TELCOM SEMICONDUCTOR, INC ]
