TC7135CPI(2002) View Datasheet(PDF) - Microchip Technology
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TC7135CPI Datasheet PDF : 22 Pages
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TC7135
4.0 ANALOG SECTION
FUNCTIONAL DESCRIPTION
4.1 Differential Inputs
The TC7135 operates with differential voltages
(+INPUT, pin 10 and -INPUT, pin 9) within the input
amplifier Common mode range, which extends from 1V
below the positive supply to 1V above the negative
supply. Within this Common mode voltage range, an
86dB Common mode rejection ratio is typical.
The integrator output also follows the Common mode
voltage and must not be allowed to saturate. A worst-
case condition exists, for example, when a large posi-
tive Common mode voltage with a near full scale neg-
ative differential input voltage is applied. The negative
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 4V full scale swing, with some loss of
accuracy. The integrator output can swing within 0.3V
of either supply without loss of linearity.
4.2 Analog Common Input
ANALOG COMMON is used as the -INPUT return dur-
ing auto zero and de-integrate. If -INPUT is different
from ANALOG COMMON, a Common mode voltage
exists in the system. However, this signal is rejected by
the excellent CMRR of the converter. In most applica-
tions, –INPUT will be set at a fixed, known voltage
(power supply common, for instance). In this applica-
tion, ANALOG COMMON should be tied to the same
point, thus removing the Common mode voltage from
the converter. The reference voltage is referenced to
ANALOG COMMON.
4.3 Reference Voltage Input
The reference voltage input (REF IN) must be a posi-
tive voltage with respect to ANALOG COMMON. A
reference voltage circuit is shown in Figure 4-1.
FIGURE 4-1:
USING AN EXTERNAL
REFERENCE
V+
V+
TC7135
REF
IN
ANALOG
COMMON
10k
10k
MCP1525
2.5 VREF
1µF
Analog Ground
DS21460B-page 8
© 2002 Microchip Technology Inc.
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