3-1/2 DIGIT A/D CONVERTERS
TC7106
TC7106A
TC7107
TC7107A
V+
+
VREF
–
VREF
IZ
V+
V+
6.8kΩ
V+
+
V
IN
–
+
–
+
INPUT
BUFFER
C
I
R
I
–
V
I
INTEGRATOR
TI
V
I
=
V
CM
– V
IN
RI CI
Where:
4000
T
I
= INTEGRATION TIME =
6.8V
ZENER
TC7106A
20k
Ω
TC7107A
+
VREF
–
VREF
COMMON
TC04
1.2V
REF
TC7106A
TC7107A
V
CM
[
[
f
OSC
C
I
= INTEGRATION CAPACITOR
R
I
= INTEGRATION RESISTOR
Figure 9.
Common-Mode Voltage Reduces Available Integrator
Swing. (V
COM
≠
V
IN
)
(a)
(b)
Figure 7. External Reference
DEVICE PIN FUNCTIONAL DESCRIPTION
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 (V
CM
). 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 V
IN
is connected to analog common (V
COM
):
See Figure 8.
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 V
CM
exists in
conjunction with a full-scale negative differential signal. The
negative signal drives the integrator output positive along
with V
CM
(Figure 9). For such applications the integrator
output swing can be reduced below the recommended 2.0V
full-scale swing. The integrator output will swing within 0.3V
of V
+
or V
–
without increasing linearity errors.
Differential Reference
+
–
(V
REF
(Pin 36), V
REF
(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, C
REF
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.
SEGMENT
DRIVE
LCD DISPLAY
MEASURED
SYSTEM
V+
V–
V+ V –
VBUF
V+IN
V –IN
CAZ
VINT
POL BP
OSC1
OSC3
OSC2
V–
GND
TC7106A
ANALOG
–
+
+
COMMON VREF VREF V
GND
POWER
SOURCE
+
9V
–
Figure 8. Common-Mode Voltage Removed in Battery Operation with V
IN
= Analog Common
3-194
TELCOM SEMICONDUCTOR, INC.
TELCOM [ TELCOM SEMICONDUCTOR, INC ]
