TC7107 TelCom, TC7107 Datasheet - Page 11

• Manufacturer Part Number: TC7107
• Description: 3-1/2 DIGIT A/D CONVERTERS
• Manufacturer: TelCom

Integrating Capacitor – C
output voltage swing without causing output saturation. Due
to the TC7106A/7107A superior temperature coefficient
specification, analog common will normally supply the differ-
ential voltage reference. For this case a
integrator output swing is satisfactory. For 3 readings/
second (f
different oscillator frequency is used, C
in inverse proportion to maintain the nominal 2 V integrator
swing.
rollover error. A polypropylene capacitor is recommended.
Integrating Resistor – R
with class A output stages. The output stage idling current
is 100 A. The integrator and buffer can supply 20 A drive
currents with negligible linearity errors. R
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
470k .
Component
Value
C
R
C
Note:1.
3-1/2 DIGIT A/D CONVERTERS
AZ
INT
INT
C
An exact expression for C
C
Where:
f
V
R
V
C
The input buffer amplifier and integrator are designed
OSC
TELCOM SEMICONDUCTOR, INC.
FS
INT
INT
INT
INT
INT
f
= Full-scale input voltage
OSC
= Clock frequency at Pin 38
= Desired full-scale integrator output swing
= Integrating resistor
must have low dielectric absorption to minimize
should be selected to maximize the integrator
OSC
=
= 48kHz (3 readings/sec)
(4000) (
= 48kHz) a 0.22 F value is suggested. If a
f
V
INT
OSC
INT
1
Nominal Full-Scale Voltage
is 47k . 2.0V full-scale requires
200.0mV
) (
0.47 F
0.22 F
R
47k
V
INT
INT
INT
FS
INT
is:
)
INT
must be changed
INT
0.047 F
2.000V
0.22 F
470k
2V full-scale
is chosen to
Oscillator Components
selected using the equation:
internal control clock. The backplane drive signal is derived
by dividing f
the signal-integrate period should be a multiple of 60Hz.
Oscillator frequencies of 240kHz, 120kHz, 80kHz, 60kHz,
48kHz, 40kHz, etc. should be selected. For 50 Hz rejection,
oscillator frequencies of 200kHz, 100kHz, 66 2/3kHz, 50kHz,
40kHz, etc. would be suitable. Note that 40kHz (2.5 read-
ings/second) will reject both 50Hz and 60Hz.
Reference Voltage Selection
signal be twice the reference voltage.
Required Full-Scale Voltage*
200.0mV
2.000V
* V
exist between a transducer output voltage and the required
digital reading. Assume, for example, a pressure transducer
output is 400mV for 2000 lb/in
input voltage by two the reference voltage should be set to
200mV. This permits the transducer input to be used
directly.
digital zero reading is required when V
This is common in temperature measuring instrumentation.
A compensating offset voltage can be applied between
analog common and V
nected between V
analog common will normally be used to supply the convert-
er's reference. This potential is stable whenever the supply
potential is greater than approximately 7V. In applications
where an externally-generated reference voltage is desired,
refer to Figure 7.
FS
R
For f
Note that f
To achieve maximum rejection of 60Hz noise pickup,
A full-scale reading (2000 counts) requires the input
In some applications a scale factor other than unity may
The differential reference can also be used when a
The internal voltage reference potential available at
= 2 V
OSC
OSC
REF
(Pin 40 to Pin 39) should be 100k . C
OSC
of 48kHz, C
OSC
by 800.
is divided by four to generate the TC7106A
f
+
IN
OSC
and analog common.
IN
=
–
OSC
. The transducer output is con-
0.45
RC
is 100pF nominally.
2
. Rather than dividing the
IN
is not equal to zero.
100.0mV
1.000V
V
TC7106A
TC7107A
REF
TC7106
TC7107
OSC
3-193
is
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