TC826 Datasheet, PDF (1/18 Pages) TelCom Semiconductor, Inc – A/D CONVERTER WITH BAR GRAPH DISPLAY OUTPUT

TC826
Analog-to-Digital Converter with Bar Graph Display Output
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
Part Number
TC826CBU
Package
64-Pin PQFP
Temperature Range
0°C to +70°C
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 500µV. 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 5µV/°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.
© 2002 Microchip Technology Inc.
DS21477B-page 1