3-150

TELCOM SEMICONDUCTOR, INC.

3-3/4 DIGIT A/D CONVERTER WITH

FREQUENCY AND LOGIC PROBE

TC820

A "peak reading hold" input allows the TC820 to retain

the highest A/D or frequency reading. This feature is useful

in measuring motor starting current, maximum tempera-

ture, and similar applications.

A family of instruments can be created with the TC820.

No additional design effort is required to create instruments

with 3-3/4 digit resolution.

The TC820 operates from a single 9V battery, with

typical power of 10 mW. Packages include a 40-pin plastic

DIP, 44-pin plastic flat package, and 44-pin PLCC.

COMPETITIVE EVALUATION

Features Comparison

TC820

7106

3-3/4 Digit Resolution

Yes

No

Auto-Ranging Frequency Counter

Yes

No

Logic Probe

Yes

No

Decimal Point Drive

Yes

No

Peak Reading Hold

Yes

No

(Frequency or Voltage)

Display Hold

Yes

No

Simple 10:1 Range Change

Yes

No

Buzzer Drive

Yes

No

Low Battery Detection

Yes

No

With Annunciator

Overrange Detection

Yes

No

With Annunciator

Low Drift Reference

Yes

No

Underrange/Overrange

Yes

No

Logic Output

Input Overload Display

"OL"

"1"

LCD Annunciator Driver

Yes

No

LCD Drive Type

Triplexed

Direct

LCD Pin Connections

15

24

LCD Elements

36

23

GENERAL DESCRIPTION

The TC820 is a 3-3/4 digit measurement system com-

bining an integrating analog-to-digital converter, frequency

counter, and logic level tester in a single package. The

TC820 supersedes the TC7106 in new designs by improv-

ing performance and reducing system cost. The TC820

adds features that are difficult, expensive, or impossible to

provide with older A/D converters (see the competitive

evaluation). The high level of integration permits TC820-

based instruments to deliver higher performance and more

features, while actually reducing parts count. Fabricated in

low-power CMOS, the TC820 directly drives a 3-3/4 digit

(3999 maximum) LCD.

With a maximum range of 3999 counts, the TC820

provides 10 times greater resolution in the 200mV to 400mV

range than traditional 3-1/2 digit meters. An auto-zero cycle

guarantees a zero reading with a 0V input. CMOS process-

ing reduces analog input bias current to only 1pA. Rollover

error (the difference in readings for equal magnitude but

opposite polarity input signals) is less than

±1 count. Differ-

ential reference inputs permit ratiometric measurements for

ohms or bridge transducer applications.

The TC820's frequency counter option simplifies design

of an instrument well-suited to both analog and digital

troubleshooting: voltage, current, and resistance measure-

ments, plus precise frequency measurements to 4MHz

(higher frequencies can be measured with an external

prescaler), and a simple logic probe. The frequency counter

will automatically adjust its range to match the input fre-

quency, over a four-decade range.

Two logic level measurement inputs permit a TC820-

based meter to function as a logic probe. When combined

with external level shifters, the TC820 will display logic levels

on the LCD and also turn on a piezoelectric buzzer when the

measured logic level is low.

Other TC820 features simplify instrument design and

reduce parts count. On-chip decimal point drivers are in-

cluded, as is a low battery detection annunciator. A piezo-

electric buzzer can be controlled with an external switch or

by the logic probe inputs. Two oscillator options are pro-

vided: A crystal can be used if high accuracy frequency

measurements are desired, or a simple RC option can be

used for low-end instruments.