TC7116 Microchip, TC7116 Datasheet - Page 8

• Manufacturer Part Number: TC7116
• Description: 3-1/2 Digit Analog-to-Digital Converters with Hold
• Manufacturer: Microchip

TC7116/A/TC7117/A
FIGURE 3-1:
3.1.3
The final phase is reference integrate, or de-integrate.
Input low is internally connected to analog common
and input high is connected across the previously
charged reference capacitor. Circuitry within the chip
ensures that the capacitor will be connected with the
correct polarity to cause the integrator output to return
to zero. The time required for the output to return to
zero is proportional to the input signal. The digital
reading displayed is:
EQUATION 3-1:
3.1.4
The positive reference voltage (V
analog common.
3.1.5
This input can accept differential voltages anywhere
within the Common mode range of the input amplifier
or, specifically, from 1V below the positive supply to 1V
above the negative supply. In this range, the system
has a CMRR of 86dB, typical. However, since the inte-
grator also swings with the Common mode voltage,
care must be exercised to ensure that the integrator
output does not saturate. A worst case condition would
be a large, positive Common mode voltage with a near
full scale negative differential input voltage. The nega-
tive input signal drives the integrator positive, when
most of its swing has been used up by the positive
Common mode voltage. For these critical applications,
the integrator swing can be reduced to less than the
recommended 2V full scale swing with little loss of
accuracy. The integrator output can swing within 0.3V
of either supply without loss of linearity.
DS21457B-page 8
Common
Analog
V
V
IN
REFERENCE INTEGRATE PHASE
REFERENCE
DIFFERENTIAL INPUT
IN
+
-
32
31
30
V+
C
1000 =
REF
10µA
INT
AZ
INT
ANALOG SECTION OF TC7116/TC7117A AND TC7117/TC7117A
+
34
V
V
V
DE (+)
REF
REF
IN
DE
36
(–)
+
AZ
AZ & DE (±)
C
REF
REF
+) is referred to
DE (–)
DE
(+)
C
REF
33
AZ
-
V-
26
–
+
V
BUFF
V+ -3V
–
+
28
3.1.6
This pin is included primarily to set the Common mode
voltage for battery operation (TC7116/TC7116A), or for
any system where the input signals are floating, with
respect to the power supply. The analog common pin
sets a voltage approximately 2.8V more negative than
the positive supply. This is selected to give a minimum
end of life battery voltage of about 6V. However, analog
common has some attributes of a reference voltage.
When the total supply voltage is large enough to cause
the zener to regulate (>7V), the analog common volt-
age will have a low voltage coefficient (0.001%), low
output impedance (≅15Ω), and a temperature coeffi-
cient of less than 20ppm/°C, typically, and 50 ppm max-
imum. The TC7116/TC7117 temperature coefficients
are typically 80ppm/°C.
An external reference may be used, if necessary, as
shown in Figure 3-2.
FIGURE 3-2:
R
INT
Temp.
Zener
V
Low
Drift
V+
REF
35
TC7116A
TC7117A
TC7116
TC7117
ANALOG COMMON
29
Auto-Zero
C
COMMON
AZ
V+
Integrator
–
+
V
REF
TC7116A
TC7117A
Comparator
TC7116
TC7117
+
REFERENCE
USING AN EXTERNAL
©
27
20kΩ
V
C
2002 Microchip Technology Inc.
INT
INT
+
V+
1.2V REF
6.8kΩ
Section
Digital
To