TC826

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 valuable than a direct system variable readout. A bar or moving dot display supplies information precisely without 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% resolution bar display. Full –scale differential input voltage range extends from 20mV to 2V. The TC826 sensitivity is 500 µv.A low drift 35 ppm/¢XC internal reference, LCD backplane oscillator and driver, input polarity LCD driver, and overrange LCD driver make designs simple and low cost.The CMOS design required only 125 µA from a 9V battery.In +5V systems a TC7660 DC to DC converter can supply the ?V supply. The differential analog input leakage is a low 10pA. Two display formats are possible. The BAR mode display 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 overrange input signal causes the display to flash and activates the overrange 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 eliminates zero –scale adjustment potentiometers.Zero –scale drift is a low 5 µV/¢XC.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 available now for TC826 prototyping work.