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TC811

© 2001 Microchip Technology Inc.

DS21472A

3-1/2 Digit Analog-To-Digital Converter with

Hold and Differential Reference Inputs

TC811-7 11/5/96

GENERAL DESCRIPTION

The TC811 is a low power, 3-1/2 digit, LCD display

analog-to-digital converter. This device incorporates both a

display hold feature and differential reference inputs. A

crystal oscillator, which only requires two pins, permits

added features while retaining a 40-pin package. An addi-

tional feature is an "Integrator Output Zero" phase which

guarantees rapid input overrange recovery.

The TC811 display hold (HLDR) function can be used to

"freeze" the LCD display. The displayed reading will remain

indefinitely as long as HLDR is held high. Conversions

continue but the output data display latches are not updated.

The TC811 also includes a differential reference for easy

ratiometric measurements. Circuits which use the

7106/26/36 can easily be upgraded to include the hold

function with the TC811.

The TC811 has an improved internal zener reference

voltage circuit which maintains the Analog Common tem-

perature drift to 35ppm/

°C (typical) and 75ppm/°C (maxi-

mum). This represents an improvement of two to four times

over similar 3-1/2 digit converters, eliminating the need for

a costly, space consuming external reference source.

The TC811 limits linearity error to less than one count on

both the 200mV and the 2.00V full-scale ranges. Rollover

error—the difference in readings for equal magnitude but

opposite polarity input signals—is below

±1 count. High

impedance differential inputs offer 1pA leakage currents

mance guarantees a “rock solid” reading. The Auto Zero

cycle guarantees a zero display readout for a zero volt input.

The single chip CMOS TC811 incorporates all the active

devices for a 3-1/2 digit analog to digital converter to directly

drive an LCD display. On-board oscillator, precision voltage

reference and display segment and backplane drivers sim-

plify system integration, reduce board space requirements

and lower total cost. A low cost, high resolution (0.05%)

indicating meter requires only a TC811, an LCD display, five

resistors, six capacitors, a crystal, and a 9V battery. Com-

pact, hand held multimeter designs benefit from the Micro-

chip Semiconductor small footprint package option.

The TC811 uses a dual slope conversion technique

which will reject interference signals if the converters inte-

gration time is set to a multiple of the interference signal

period. This is especially useful in industrial measurement

environments where 50, 60 and 400Hz line frequency sig-

nals are present.

ABSOLUTE MAXIMUM RATINGS*

44-Pin Flat Package ......................................... 1.00W

40-Pin Plastic DIP ............................................. 1.23W

Operating Temperature Range

Commercial Package (C) ...................... 0

°C to +70°C

Industrial Package (I) ........................ – 25

°C to +85°C

Storage Temperature Range ................ – 65

°C to +150°C

Lead Temperature (Soldering, 10 sec) ................. +300

°C

*Static-sensitive device. Unused devices must be stored in conductive

material. Protect devices from static discharge and static fields. Stresses

above those listed under "Absolute Maximum Ratings" may cause perma-

nent damage to the device. These are stress ratings only and functional

operation of the device at these or any other conditions above those

indicated in the operation sections of the specifications is not implied.

Exposure to absolute maximum rating conditions for extended periods may

affect device reliability.

Symbol

Parameter

Test Conditions

Min

Typ

Max

Unit

Input

—

Zero Input Reading

– 000.0

±000.0

+000.0

Digital

Reading

—

Zero Reading Drift

—

0.2

1

µV/°C

—

Ratiometric Reading

999

999/1000

1000

Digital

Reading

NL

Linearity Error

– 1

±0.2

+1

Counts

Roll Over Error

– 1

±0.2

+1

Counts

Noise

—

15

—

Input Leakage Current

—

1

10

pA

CMRR

Common-Mode Rejection

—

50

—

µV/V