TC7109 TelCom, TC7109 Datasheet - Page 14

• Manufacturer Part Number: TC7109
• Description: 12-BIT UP-COMPATIBLE ANALOG-TO-DIGITAL CONVERTERS
• Manufacturer: TelCom

TC7109
TC7109A
Test Input
the TEST input is connected to GND, the internal clock is
disabled and the counter outputs are all forced into the HIGH
state. When the input returns to the 1/2 (V
to V
clocked to the LOW state.
input is taken to a level halfway between V
allowing the counter contents to be examined anytime.
Component Value Selection
large as possible. For example, with
COMMON connected to GND, the nominal integrator output
swing at full-scale is 4V. Since the integrator output can go
to 0.3V from either supply without significantly effecting
linearity, a 4V integrator output swing allows 0.7V for varia-
tions in output swing due to component value and oscillator
tolerances. With 5V supplies and a common-mode voltage
range of 1V required, the component values should be
selected to provide 3V integrator output swing. Noise and
3-104
V OR OPEN
The counter and its outputs may be tested easily. When
+
The counter output latches are enabled when the TEST
The integrator output swing for full-scale should be as
+
and one clock is input, the counter outputs will all be
GND
24
OSC
SEL
V
24
OSC
SEL
+
Figure 11. TC7109A Crystal Oscillator
Figure 10. TC7109A RC Oscillator
22
OSC
IN
CRYSTAL
22
OSC
IN
f
OSC
= 0.45/RC
23
OSC
OUT
23
OSC
OUT
R
C
+
25
BUFFERED
OSC OUT
–GND) voltage or
5V supplies and
25
BUFFERED
OSC OUT
+
CLOCK
and GND,
58
roll-over errors will be slightly worse than in the 4V case.
For large common-mode voltage ranges, the integrator
output swing must be reduced further. This will increase both
noise and roll-over errors. To improve performance, 6V
supplies may be used.
Integrating Capacitor
give the maximum integrator output voltage swing that will
not saturate the integrator to within 0.3V from either supply.
A 3.5V to 4V integrator output swing is nominal for the
TC7109A, with 5V supplies and analog common con-
nected to GND. For 7-1/2 conversions per second (61.72
kHz internal clock frequency), nominal values C
are 0.15 F and 0.33 F, respectively. These values should
be changed if different clock frequencies are used to main-
tain the integrator output voltage swing. The value of C
given by:
sorption to prevent roll-over errors. Polypropylene capaci-
tors give undetectable errors, at reasonable cost, up to
+85 C. Teflon
temperature range. While their dielectric absorption charac-
teristics vary somewhat between units, devices may be
selected to less than 0.5 count of error due to dielectric
absorption.
Integrating Resistor
output stage with 100 A of quiescent current. They supply
20
integrating resistor should be large enough to remain in this
very linear region over the input voltage range, but small
enough that undue leakage requirements are not placed on
the PC board. For 2.048V full-scale a 100 k
recommended and for 409.6 mV full-scale a 20 k resistor
is recommended. R
full scale by:
Auto-Zero Capacitor
noise is reduced. Since the TC7109A incorporates a zero
integrator cycle, the size of the auto-zero capacitor does not
affect overload recovery. The optimal value of the auto-zero
capacitor is between 2 and 4 times C
C
AZ
ANALOG-TO-DIGITAL CONVERTERS
The integrating capacitor, C
C
The integrating capacitor must have low dielectric ab-
The integrator and buffer amplifiers have a class A
R
As the auto-zero capacitor is made large, the system
is 0.33 F.
A of drive current with negligible nonlinearity. The
INT
INT
=
=
Integrator Output Voltage Swing
Full-Scale Voltage
(2048
®
capacitors are recommended for the military
20 A
INT
Clock Period) (20 A)
TELCOM SEMICONDUCTOR, INC.
12-BIT P-COMPATIBLE
may be selected for other values of
INT
, should be selected to
INT
. A typical value for
INT
resistor is
and C
INT
AZ
is