TC7107 TelCom, TC7107 Datasheet - Page 9

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

from a 6 volt zener diode and a large P channel source
follower. This supply is made stiff to absorb the large
capacitive currents when the backplane voltage is switched.
DIGITAL SECTION (TC7107A)
common anode LEDs. It is identical to the TC7106A except
that the regulated supply and backplane drive have been
eliminated and the segment drive is typically 8mA. The
1000's output (pin 19) sinks current from two LED segments,
and has a 16mA drive capability.
tive analog inputs. If V
can be reversed also, if desired.
System Timing
the internal decade counters. The three-phase measure-
ment cycle takes a total of 4000 counts or 16000 clock
pulses. The 4000 count cycle is independent of input signal
magnitude.
length:
•
segments are turned “ON.” The display reads –1888. During
this mode the LCD segments have a constant DC voltage
impressed. DO NOT LEAVE THE DISPLAY IN THIS MODE
FOR MORE THAN SEVERAL MINUTES! LCD displays
may be destroyed if operated with DC levels for extended
periods.
shown in Figure 4.
3-1/2 DIGIT A/D CONVERTERS
Auto-Zero Phase: 1000 to 3000 Counts
For signals less than full-scale, the auto-zero phase is
assigned the unused reference integrate time period.
In the TC7106A, an internal digital ground is generated
Figure 5 shows the TC7107A. It is designed to drive
In both devices, the polarity indication is “ON” for nega-
The display font is the same as the TC7106A.
The oscillator frequency is divided by 4 prior to clocking
Each phase of the measurement cycle has the following
When the TEST pin on the TC7106A is pulled to V
The display font and the segment drive assignment are
TELCOM SEMICONDUCTOR, INC.
Figure 4. Display Font and Segment Assignment
1000's
IN
–
100's
DISPLAY FONT
(4000 to 12000 Clock Pulses)
and V
IN
+
are reversed, this indication
10's
1's
+
, all
•
•
7106/7107 parts. External component value changes are
not required to benefit from the low drift internal reference.
Clock Circuit
COMPONENT VALUE SELECTION
noise. A 0.47 F capacitor is recommended for 200mV full-
scale applications where 1 LSB is 100 V. A 0.047 F capaci-
tor is adequate for 2.0V full-scale applications. A mylar
dielectric capacitor is adequate.
Reference Voltage Capacitor – C
output voltage back to zero during the reference-integrate
cycle is stored on C
when V
voltage exists (V
requires 200mV full-scale, increase C
error will be held to less than 1/2 count. A mylar dielectric
capacitor is adequate.
Auto-Zero Capacitor – C
EXT
OSC
Signal Integrate: 1000 Counts
This time period is fixed. The integration period is:
Where f
Reference Integrate: 0 to 2000 Counts
The TC7106A/7107A are drop-in replacements for the
Three clocking methods may be used:
1. An external oscillator connected to pin 40.
2. A crystal between pins 39 and 40.
3. An R-C oscillator using all three pins.
The C
The reference voltage used to ramp the integrator
IN
–
is tied to analog common. If a large common-mode
AZ
OSC
RC NETWORK
40
capacitor size has some influence on system
CRYSTAL
TO TEST PIN ON TSC7106A
TO GND PIN ON TSC7107A
is the externally set clock frequency.
T
REF
–
SI
Figure 6. Clock Circuits
= 4000
REF
(4000 Clock Pulses)
analog common) and the application
. A 0.1 F capacitor is acceptable
(0 to 8000 Clock Pulses)
39
[ ]
f
OSC
AZ
1
REF
38
to 1.0 F. Rollover
÷
4
REF
TC7106A
TC7107A
TC7106A
TC7107A
TC7106
TC7107
TO
COUNTER
3-191
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