4-1/2 DIGIT ANALOG-TO-DIGITAL
CONVERTER WITH ON-CHIP LCD DRIVERS
TC7129
±
5V Power Supply
Measurements are made with respect to power supply
ground. DGND (pin 36) is set internally to about 5V less than
V
+
(pin 24); it is not intended as a power supply input and
must not be tied directly to power supply ground. (It can be
used as a reference for external logic, as explained in
"Connecting to External Logic." (See Figure 2.)
+5V
24
V
+
REF HI
36
34
TC04
35
28
33
32
+
3.8V
TO
6V
DGND
REF LO
COM
TC7129
IN HI
+
VIN
24
+
V
0.1 µF
REF HI
8
34
2
IN LO
–
V
–
TC04
REF LO
35
28
33
32
3
+
10 µF
23
TC7660
4
5
36
0.1 µF
DGND
COM
IN HI
10 µF
+
VIN
–
+
Figure 3. Powering the TC7129 From a Low-Voltage Battery
TC7129
0.1 µF
IN LO
–
V
23
+5V
–5V
Figure 2.
Powering the TC7129 From a
±
5V Power Supply
24
V
+
0.1 µF
35
36
0.1 µF
33
DGND
28
34
Low-Voltage Battery Source
A battery with voltage between 3.8V and 6V can be used
to power the TC7129 when used with a voltage-doubler
circuit as shown in Figure 3. The voltage doubler uses the
TC7660 DC-to-DC voltage converter and two external ca-
pacitors.
TC04
+
VIN
+5V Power Supply
Measurements are made with respect to power supply
ground. COMMON (pin 28) is connected to REF LO (pin 35).
A voltage doubler is needed, since the supply voltage is less
than the 6V minimum needed by the TC7129. DGND (pin
36) must be isolated from power supply ground.
(See Figure 4.)
8
V
+
2
TC7129
32
V–
–
+
10 µF
23
TC7660
GND
3
4
5
10 µF
Connecting to External Logic
External logic can be directly referenced to DGND (pin
36), provided that the supply current of the external logic
does not exceed the sink current of DGND (Figure 5). A safe
value for DGND sink current is 1.2 mA. If the sink current is
expected to exceed this value, a buffer is recommended.
(See Figure 6.)
3-238
+
Figure 4. Powering the TC7129 From a +5V Power Supply
TELCOM SEMICONDUCTOR, INC.
TELCOM [ TELCOM SEMICONDUCTOR, INC ]
