tc7107a Microchip Technology Inc., tc7107a Datasheet - Page 13

• Manufacturer Part Number: tc7107a
• Description: 3-1/2 Digit Analog-to-digital Converters
• Manufacturer: Microchip Technology Inc.

7.0
7.1
The C
noise. A 0.47μF capacitor is recommended for 200mV
full scale applications where 1LSB is 100μV. A 0.047μF
capacitor is adequate for 2.0V full scale applications. A
mylar type dielectric capacitor is adequate.
7.2
The reference voltage used to ramp the integrator out-
put voltage back to zero during the reference integrate
cycle is stored on C
when V
mode voltage exists (V
application requires 200mV full scale, increase C
1.0μF. Rollover error will be held to less than 1/2 count.
A mylar dielectric capacitor is adequate.
7.3
C
put voltage swing without causing output saturation.
Due to the TC7106A/7107A superior temperature
coefficient specification, analog common will normally
supply the differential voltage reference. For this case,
a ±2V full scale integrator output swing is satisfactory.
For 3 readings/second (F
is suggested. If a different oscillator frequency is used,
C
the nominal ±2V integrator swing.
An exact expression for C
EQUATION 7-1:
C
rollover
recommended.
© 2006 Microchip Technology Inc.
Where:
INT
INT
INT
F
V
R
V
should be selected to maximize the integrator out-
must be changed in inverse proportion to maintain
must have low dielectric absorption to minimize
AZ
OSC
FS
INT
INT
IN
COMPONENT VALUE
SELECTION
Auto-Zero Capacitor (C
Reference Voltage Capacitor
(C
Integrating Capacitor (C
capacitor size has some influence on system
- is tied to analog common. If a large Common
= Clock Frequency at Pin 38
= Full Scale Input Voltage
= Integrating Resistor
= Desired Full Scale Integrator Output Swing
error.
C
REF
INT
)
=
(4000)
A
REF
. A 0.1μF capacitor is acceptable
REF
polypropylene
OSC
⎛
⎝
INT
- – analog common) and the
F
V
OSC
1
INT
= 48kHz), a 0.22μF value
is:
⎞
⎠
⎛
⎝
R
V
INT
FS
AZ
⎞
⎠
INT
capacitor
)
)
REF
to
is
7.4
The input buffer amplifier and integrator are designed
with class A output stages. The output stage idling
current is 100μA. The integrator and buffer can supply
20μA drive currents with negligible linearity errors. R
is chosen to remain in the output stage linear drive
region, but not so large that printed circuit board
leakage currents induce errors. For a 200mV full scale,
R
7.5
R
selected using the equation:
EQUATION 7-2:
For F
Note that F
TC7106A internal control clock. The backplane drive
signal is derived by dividing F
To achieve maximum rejection of 60Hz noise pickup,
the signal integrate period should be a multiple of
60Hz. Oscillator frequencies of 240kHz, 120kHz,
80kHz, 60kHz, 48kHz, 40kHz, etc. should be selected.
For 50Hz rejection, oscillator frequencies of 200kHz,
100kHz, 66-2/3kHz, 50kHz, 40kHz, etc. would be
suitable. Note that 40kHz (2.5 readings/second) will
reject both 50Hz and 60Hz.
7.6
A full scale reading (2000 counts) requires the input
signal be twice the reference voltage.
Component
Required Full Scale Voltage*
* V
INT
OSC
Note:
TC7106/A/TC7107/A
Value
R
C
is 47kΩ. 2.0V full scale requires 470kΩ.
FS
C
OSC
INT
INT
(Pin 40 to Pin 39) should be 100kΩ. C
AZ
= 2V
Integrating Resistor (R
Oscillator Components
Reference Voltage Selection
of 48kHz, C
F
200.0mV
OSC
2.000V
REF.
OSC
is divided by four to generate the
= 48kHz (3 readings per sec).
200.0mV
Nominal Full Scale Voltage
F
0.47μF
0.22μF
OSC
OSC
47kΩ
=
is 100pF nominally.
0.45
RC
OSC
by 800.
DS21455C-page 13
INT
100.0mV
1.000V
0.047μF
2.000V
V
0.22μF
470kΩ
)
REF
OSC
INT
is