3-238

TELCOM SEMICONDUCTOR, INC.

TC7129

4-1/2 DIGIT ANALOG-TO-DIGITAL

CONVERTER WITH ON-CHIP LCD DRIVERS

Figure 2.

Powering the TC7129 From a

V–

V

+

REF HI

REF LO

IN HI

COM

IN LO

DGND

VIN

+

–

–5V

0.1 µF

+5V

0.1 µF

24

34

35

28

33

32

23

36

TC7129

TC04

0.1 µF

Measurements are made with respect to power supply

ground. DGND (pin 36) is set internally to about 5V less than

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.)

V–

TC7129

V

REF HI

REF LO

IN HI

COM

IN LO

DGND

3.8V

TO

6V

+

+

10 µF

+

8

2

4

10 µF

TC04

+

–

3

TC7660

VIN

5

24

+

34

35

28

33

32

23

36

Figure 3. Powering the TC7129 From a Low-Voltage Battery

V–

V

DGND

+

10 µF

+

8

2

4

10 µF

TC04

+

–

3

VIN

5

24

+

34

35

28

33

32

23

36

TC7660

GND

0.1 µF

0.1 µF

+5V

TC7129

Figure 4. Powering the TC7129 From a +5V Power Supply

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.

+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.)

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.)