3-243

TELCOM SEMICONDUCTOR, INC.

7

6

5

4

3

1

2

8

TC7129

4-1/2 DIGIT ANALOG-TO-DIGITAL

CONVERTER WITH ON-CHIP LCD DRIVERS

Figure 13.

Integrator Block Diagram

The buffer amplifier has a common-mode input voltage

amplifier can swing to within 0.3V of the rails, although for

best linearity the swing is usually limited to within 1V. Both

amplifiers can supply up to 80

µA of output current, but

should be limited to 20

µA for good linearity.

Continuity Indicator

A comparator with a 200 mV threshold is connected

between IN HI (pin 33) and IN LO (pin 32). Whenever the

voltage between inputs is less than 200 mV, the

CONTINUITY output (pin 27) will be pulled HIGH, activating

the continuity annunciator on the display. The continuity

pin can also be used as an input to drive the continuity

annunciator directly from an external source. A schematic

of the input/output nature of this pin is shown in Figure 15.

Figure 14.

Continuity Indicator Circuit

COM

BUFFER

200 mV

IN HI

–

+

IN LO

–

+

V

CONT

500 k

Ω

TO DISPLAY

DRIVER

(NOT LATCHED)

TC7129

COMMON

REF HI

BUFFER

INTE-

GRATOR

DE

ZI, X10

COMPARATOR 1

200 mV

CREF

RINT

CINT

INT1

IN HI

+

–

–

+

–

+

REF LO

DE

IN LO

–

+

DE–

DE+

DE+

DE–

100 pF

V

–

+

CONTINUITY

INT1, INT2

CONTINUITY

COMPARATOR

500 k

Ω

REST

TO DISPLAY DRIVER

10

pF

COMPARATOR 2

TO DIGITAL

SECTION

TC7129

INT

X10

Table I. Switch Legends

Label

Meaning

DE

Open during all deintegrate phases.

DE–

Closed during all deintegrate phases when input

voltage is negative.

DE+

Closed during all deintegrate phases when input

voltage is positive.

Closed during the first integrate phase

(measurement of the input voltage).

Closed during the second integrate phase

(measurement of the amplifier offset).

INT

Open during both integrate phases.

REST

Closed during the rest phase.

ZI

Closed during the zero-integrate phase.

X10

Closed during the X10 phase.

X10

Open during the X10 phase.