TC811 TelCom Semiconductor, TC811 Datasheet - Page 9

• Manufacturer Part Number: TC811
• Description: 3-1/2 DIGIT A/D CONVERTER WITH HOLD AND DIFFERENTIAL REFERENCE INPUTS
• Manufacturer: TelCom Semiconductor

3-1/2 DIGIT A/D CONVERTER WITH HOLD AND
DIFFERENTIAL REFERENCE INPUTS
DEVICE PIN FUNCTIONAL DESCRIPTION
Differential Signal Inputs (V
V
accepts input signals within the input stage common mode
voltage range (V
1.5V. Common-mode voltages are removed from the sys-
tem when the TC811 operates from a battery or floating
power source (isolated from measured system) and V
connected to Analog Common. (see Figure 8)
86dB common-mode rejection ratio minimizes error. Com-
mon-mode voltages do, however, affect the integrator out-
put level. A worse case condition exists if a large positive
V
tial signal. The negative signal drives the integrator output
positive along with V
integrator output swing can be reduced below the recom-
mended 2.0V full-scale swing. The integrator output will
swing within 0.3V of V
error.
Reference (V
ence as well as the “hold” function. The differential reference
CM
IN
Freq. (kHz)
Oscillator
–
The TC811 is designed with true differential inputs and
In systems where common-mode voltages exist, the
Unlike the ICL7116, the TC811 has a differential refer-
exists in conjunction with a full-scale negative differen-
32.768
TELCOM SEMICONDUCTOR, INC.
(Pin 30))
40
V +
SOURCE
POWER
+
CM
REF
V –
RINT
). The typical range is V
180k
150k
CM
Figure 7. Common-Mode Voltage Removed in Battery Operation With V
(Pin 36), V
GND
(Figure 8). For such applications the
+
200mV
MEASURED
V +
V
Full-Scale Voltage (V
Figure 6b.
or V
SYSTEM
–
0.068 F
0.068 F
–
CINT
GND
without increased linearity
–
REF
IN
+
RINT
(Pin 31),
(Pin 33)
1.8M
1.5M
+
2.0V
– 1.0 to V
ANALOG
COMMON
V
V +
FS
V BUF
–
0.068 F
0.068 F
)
CINT
IN
–
–
V REF
is
+
C AZ
–
TC811
V REF
+
inputs permit ratiometric measurements and simplify inter-
facing with sensors such as load cells and temperature
sensors. The TC811 is ideally suited to applications in hand-
held multimeters, panel meters, and portable instrumenta-
tion. The reference voltage can be generated anywhere
within the V
large common-mode voltages, C
pared to stray node capacitance. A 0.1 F capacitor is a
typical value.
mon temperature coefficient. This provides a very stable
voltage suitable for use as a voltage reference. The tem-
perature coefficient of Analog Common is typically
35ppm/ C.
V INT
–
+
V
V
V +
To prevent rollover type errors from being induced by
The TC811 offers a significantly improved Analog Com-
IN
CM
Figure 8.
SEGMENT
+
DRIVE
9V
POL
+
+
–
OSC 1
OSC 2
V –
to V
INPUT
BUFFER
Common-Mode Voltage Reduces Available
BP
Integrator Swing. (V
Where:
–
LCD DISPLAY
power supply range.
20M
–
IN
= Analog Common
C
R
V
T
I
I
I
I
=
R
=
=
=
470k
R I C I
I
INTEGRATION TIME
INTEGRATION CAPACITOR
INTEGRATION RESISTOR
T I
COM
[
REF
V
40kHZ
CM
20 pF
10pF
should be large com-
–
+
V
C
IN
–
I
INTEGRATOR
)
V
IN
[
V +
V +
TC811
=
V
4000
f
OSC
I
3-145
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