© 2002 Microchip Technology Inc.

DS21477B-page 1

TC826

Features

• Bipolar A/D Conversion

• 2.5% Resolution

• Direct LCD Display Drive

• ‘Thermometer’ BAR or DOT Display

• 40 Data Segments Plus Zero

• Over Range Plus Polarity Indication

• Precision On-Chip Reference: 35ppm/°C

• Differential Analog Input

• Low Input Leakage: 10pA

• Display Flashes on Over Range

• Display HOLD Mode

• Auto-Zero Cycle Eliminates Zero Adjust

Potentiometer

• 9V Battery Operation

• Low Power Consumption: 1.1mW

• 20mV to 2.0V Full Scale Operation

• Non-Multiplexed LCD Drive for Maximum

Viewing Angle

Device Selection Table

General Description

In many applications, a graphical display is preferred

over a digital display. Knowing a process or system

operates, for example, within design limits is more valu-

able than a direct system variable read out. A bar or

moving dot display supplies information precisely with-

out requiring further interpretation by the viewer.

The TC826 is a complete analog-to-digital converter

with direct liquid crystal (LCD) display drive. The 40

LCD data segments plus zero driver give a 2.5% reso-

lution bar display. Full scale differential input voltage

range extends from 20mV to 2V. The TC826 sensitivity

is 500

µV. A low drift 35ppm/°C internal reference, LCD

backplane oscillator and driver, input polarity LCD

driver, and over range LCD driver make designs simple

and low cost. The CMOS design required only 125µA

from a 9V battery. In +5V systems, a TC7660 DC to DC

converter can supply the -5V supply. The differential

analog input leakage is a low 10pA.

Two display formats are possible. The BAR mode dis-

play is like a ‘thermometer’ scale. The LCD segment

driver that equals the input, plus all below it are on. The

DOT mode activates only the segment equal to the

input. In either mode, the polarity signal is active for

negative input signals. An over range input signal

causes the display to flash and activates the over range

annunciator. A HOLD mode can be selected that

freezes the display and prevents updating.

The dual slope integrating conversion method with

auto-zero phase maximizes noise immunity and elimi-

nates zero scale adjustment

potentiometers. Zero

scale drift is a low 5

µV/°C. Conversion rate is typically

5 per second and is adjustable by a single external

resistor.

A compact, 0.5" square, flat package minimizes PC

board area. The high pin count LSI package makes

multiplexed LCD displays unnecessary. Low cost,

direct drive LCD displays offer the widest viewing angle

and are readily available. A standard display is avail-

able now for TC826 prototyping work.

Part Number

Package

Temperature Range

TC826CBU

64-Pin PQFP

0

°Cto +70°C

Analog-to-Digital Converter with Bar Graph Display Output