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.)
24
+
V
34
REF HI
TC04
36
DGND
+
3.8V
TO
6V
35
28
REF LO
COM
+5V
TC7129
+
33
32
IN HI
V
IN
8
24
IN LO
+
–
V
2
–
V
34
REF HI
0.1 µF
+
23
TC04
10 µF
4
5
35
TC7660
3
REF LO
36
DGND
28
COM
0.1 µF
10 µF
33
+
+
IN HI
V
TC7129
IN LO
IN
–
32
Figure 3. Powering the TC7129 From a Low-Voltage Battery
0.1 µF
–
V
23
+
5V
–5V
Figure 2. Powering the TC7129 From a ±5V Power Supply
24
+
Low-Voltage Battery Source
V
34
0.1 µF
TC04
Abatterywithvoltagebetween3.8Vand6Vcanbeused
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.
35
28
36
DGND
0.1 µF
+
33
32
+5V Power Supply
TC7129
V
IN
8
+
Measurements are made with respect to power supply
ground. COMMON(pin28)isconnectedtoREFLO(pin35).
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.)
–
V
–
2
V
23
+
10 µF
4
5
TC7660
GND
3
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
doesnotexceedthesinkcurrentofDGND(Figure5). Asafe
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.)
Figure 4. Powering the TC7129 From a +5V Power Supply
3-238
TELCOM SEMICONDUCTOR, INC.
TELCOM [ TELCOM SEMICONDUCTOR, INC ]
