TC7126 TelCom, TC7126 Datasheet - Page 10

• Manufacturer Part Number: TC7126
• Description: 3-1/2 DIGIT ANALOG-TO-DIGITAL CONVERTERS
• Manufacturer: TelCom

TC7126
TC7126A
100 A. This FET will hold the common line at 3V should an
external load attempt to pull the common line toward V
Analog common source current is limited to 1 A. Therefore,
analog common is easily pulled to a more negative voltage
(i.e., below V
puts to analog common during the auto-zero phase. During
the reference-integrate phase, V
common. If V
mon, a common-mode voltage exists, but is rejected by the
converter's 86 dB common-mode rejection ratio. In battery
operation, analog common and V
removing common-mode voltage concerns. In systems where
V
voltage, analog common should be connected to V
tion reference, or common point. The TC7126A is specifi-
cally designed to operate from a battery or in any measure-
ment system where input signals are not referenced (float)
3-226
Figure 6. Common-Mode Voltage Reduces Available Integrator
IN
–
The TC7126A connects the internal V
The analog common pin serves to set the analog sec-
–
+
is connected to power supply ground or to a given
V
V
IN
CM
Swing (V
+
+
IN
+
–
– 3V).
INPUT
BUFFER
is not externally connected to analog com-
COM
V +
Where:
SOURCE
POWER
Figure 5. Common-Mode Voltage Removed in Battery Operation With V
V
V –
IN
)
C
R
V
T
GND
I
I
I
I
R
=
=
=
=
MEASURED
V +
V –
I
SYSTEM
Integration time
Integration capacitor
Integration resistor
R I C I
T I
IN
–
–
IN
GND
is connected to analog
are usually connected,
[
V
–
+
C
CM
I
INTEGRATOR
–
+
IN
V
=
IN
and V
4000
f
[
OSC
ANALOG
COMMON
V
V –
IN
–
V BUFF
IN
IN
+
V
.
IN
–
I
in-
+
.
V REF
–
C AZ
with respect to the TC7126A's power source. The analog
common potential of V
voltage. The common potential has a 0.001%/% voltage
coefficient and a 15 output impedance.
analog common is a very stable potential with excellent
temperature stability (typically 35 ppm/ c). This potential
can be used to generate the TC7126A's reference voltage.
An external voltage reference will be unnecessary in most
cases because of the 35 ppm/ C temperature coefficient.
See "TC7126A Internal Voltage Reference" discussion.
TEST (Pin 37)
used as the negative power supply connection for external
CMOS logic. The TEST pin is tied to the internally-generated
negative logic supply through a 500 resistor. The TEST pin
load should not be more than 1 mA. See "Digital Section" for
additional information on using TEST as a negative digital
logic supply.
minus sign will be activated. DO NOT OPERATE IN THIS
MODE FOR MORE THAN SEVERAL MINUTES. With
TEST= V
voltage which will destroy the LCD.
TC7126A Internal Voltage Reference
stability has been significantly improved (Figure 7). The "A"
version of the industry-standard TC7126 device allows
users to upgrade old systems and design new systems
without external voltage references. External R and C val-
ues do not need to be changed. Figure 10 shows analog
common supplying the necessary voltage reference for the
TC7126A.
TC7126A
V REF
ANALOG-TO-DIGITAL CONVERTERS
+
With sufficiently high total supply voltage (V
The TEST pin potential is 5V less than V
If TEST is pulled HIGH (to V
The TC7126A's analog common voltage temperature
V INT
V +
+
, the LCD segments are impressed with a DC
SEGMENT
+
DRIVE
9V
POL
OSC 1
OSC 3
OSC 2
V –
BP
IN
TELCOM SEMICONDUCTOR, INC.
= Analog Common
+
–3V gives a 7V end of battery life
LCD
+
), all segments plus the
3-1/2 DIGIT
+
. TEST may be
+
–V
–
>7V),