3-71

TELCOM SEMICONDUCTOR, INC.

7

6

5

4

3

1

2

8

20

k

6.8 k

Ω

Ω

V+

1.25V REF

TC04

V+

REF

IN

6.8V

ZENER

V+

V–

V+

ANALOG

GROUND

ANALOG

COMMON

REF

IN

ANALOG

COMMON

TC835

TC835

LATCH

LATCH

LATCH

LATCH

LATCH

COUNTERS

CONTROL LOGIC

MULTIPLEXER

POLARITY

D5

D4

D3

D2

D1

13 B1

14 B2

15 B4

16 B8

POLARITY

FF

MSB

DIGIT

DRIVE

SIGNAL

LSB

DATA

OUTPUT

24

22

25

27

28

26

21

DIGITAL

GND

CLOCK

IN

RUN/

HOLD

OVER–

RANGE

STROBE

BUSY

UNDER–

RANGE

ZERO

CROSS

DETECT

FROM

ANALOG

SECTION

INTEGRATOR

OUTPUT

OVERRANGE

WHEN

APPLICABLE

UNDERRANGE

WHEN

APPLICABLE

SYSTEM

ZERO

10,001

COUNTS

SIGNAL

INTE

10,000

COUNTS

(FIXED)

REFERENCE

INTEGRATE

20,001

COUNTS (MAX)

FULL MEASUREMENT CYCLE

40,002 COUNTS

BUSY

EXPANDED SCALE

BELOW

D5

D4

D3

D2

D1

100

COUNTS

DIGIT SCAN

STROBE

AUTO ZERO

SIGNAL

INTEGRATE

REFERENCE

INTEGRATE

D5

D4

D3

D2

D1

DIGIT SCAN

FOR

OVERRANGE

FIRST D5 OF SYSTEM ZERO

AND REFERENCE INTEGRATE

ONE COUNT LONGER.

*

*

*

Figure 5. Using an External Reference

Figure 7. Timing Diagrams for Outputs

Figure 6. Digital Section Functional Diagram

Digital Section Functional Description

The major digital subsystems within the TC835 are

illustrated in Figure 6, with timing relationships shown in

Figure 7. The multiplexed BCD output data can be displayed

on LCD or LED display with the TC7211A (LCD)

4-digit display driver.

The digital section is best described through a discus-

sion of the control signals and data outputs.

RUN/HOLD Input (Pin 25)

When left open, this pin assumes a logic "1" level. With

a R/H = 1, the TC835 performs conversions continuously,

with a new measurement cycle beginning every 40,002

clock pulses.

When R/H changes to a logic "0," the measurement

cycle in progress will be completed, and data held and

displayed as long as the logic "0" condition exists.

A positive pulse (>300nsec) at R/H initiates a new

measurement cycle. The measurement cycle in progress

when R/H initially assumed the logic "0" state must be

completed before the positive pulse can be recognized as a

single conversion run command.

TC835

PERSONAL COMPUTER

DATA ACQUISITION A/D CONVERTER