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TC811 3-1/2 DIGIT A/D CONVERTER WITH HOLD AND DIFFERENTIAL REFERENCE INPUTS
FEATURES
s s s s s s s s s s s s s s Differential Reference Input Display Hold Function Fast Over-Range Recovery, Guaranteed Next Reading Accuracy Low Temperature Drift Internal Reference ....................................... 35ppm/°C (Typ) Guaranteed Zero Reading With Zero Input Low Noise ..................................................... 15µVp-p High Resolution (0.05%) and Wide Dynamic Range (72 dB) High Impedance Differential Input Low Input Leakage Current ....................... 1pA Typ 10pA Max Direct LCD Drive – No External Components Precision Null Detection with True Polarity at Zero Crystal Clock Oscillator Available in DIP, Compact Flat Package or PLCC Convenient 9V Battery Operation with Low Power Dissipation (600µA Typical, 1mW Maximum)
2 3 4
Max VREF Tempco
TYPICAL APPLICATIONS
s s Thermometry Digital Meters — Voltage/Current/Power — pH Measurement — Capacitance/Inductance — Fluid Flow Rate/Viscosity — Humidity — Position Panel Meters LVDT Indicators Portable Instrumentation Digital Scales Process Monitors Gaussometers Photometers
s s s s s s s
ORDERING INFORMATION
Part No. Package Temp. Range
FUNCTIONAL BLOCK DIAGRAM
TC811CKW 44-PQFP 0°C to +70°C 75 ppm/°C TC811CPL 40-Pin Plastic DIP 0°C to +70°C 75 ppm/°C
5 6 7
TYPICAL SEGMENT OUTPUT + V 0.5mA SEGMENT OUTPUT 2mA
LCD DISPLAY
TC811CPL
INTERNAL DIGITAL GROUND BACKPLANE 21
+ C REF
+ VREF 35 36
CREF
– VREF 33
RINT – V BUFF C REF 34 28 V + 38
CAZ
CINT VINT LCD SEGMENT DRIVERS
29 INTEGRATOR
27 TO DIGITAL SECTION 7 SEGMENT DECODE 7 SEGMENT DECODE 7 SEGMENT DECODE 200
10 µA 31 INT A/Z 32
ZI & A/Z
ZI & A/Z
– + ZI
– +
+ –
DATA LATCH
A/Z COMPARATOR
THOUSANDS HUNDREDS TENS UNITS
+ V IN
DE (–)
DE (+) – LOW TEMPCO VREF
ANALOG COMMON
DE (+)
DE (–)
+ V+– 3.0V
TO SWITCH DRIVERS FROM COMPARATOR OUTPUT CLOCK fOSC ≈70kΩ 4 CONTROL LOGIC
38 6.2V
V+
– 30 V IN INT
AZ & DE (±) 26 –
INTERNAL DIGITAL GOUND
V
VTH = 1V 1
500Ω 26
TEST
40 OSC 1
39 22MΩ OSC 2
V–
HLDR
470k V + 10pF kH 20pF V +
8
TC811-7 11/5/96
TELCOM SEMICONDUCTOR, INC.
3-137
3-1/2 DIGIT A/D CONVERTER WITH HOLD AND DIFFERENTIAL REFERENCE INPUTS TC811
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 additional 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 temperature drift to 35ppm/°C (typical) and 75ppm/°C (maximum). 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 and a 1012Ω input impedance. The 15µVp-p noise performance 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. Onboard oscillator, precision voltage reference and display segment and backplane drivers simplify 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. Compact, hand held multimeter designs benefit from the TelCom Semiconductor small footprint package option. The TC811 uses a dual slope conversion technique which will reject interference signals if the converters integration 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 signals are present.
ABSOLUTE MAXIMUM RATINGS*
Supply Voltage (V+ to V –)............................................ 15V Analog Input voltage (Either Input)1 ..................... V+ to V – Reference Input Voltage ...................................... V+ to V – Clock Input ..............................