TC811 TELCOM | Alldatasheet
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3-137TELCOM SEMICONDUCTOR, INC. TC811 TC811CPL THOUSANDS HUNDREDS TENS UNITS OSC V TEST TO SWITCH DRIVERS FROM COMPARATOR OUTPUT CLOCK
7 SEGMENT
500Ω DATA LATCH BUFFC REF R INT V + C AZ VINT 28 29 27343635 µA ZI & A/Z INT AZ & DE (–) INT 26 INTEGRATOR TO DIGITAL SECTION DE (+) DE (–) DE (+) DE (–)ANALOG COMMON C REF V IN V IN V C INT VREF + VREF ZI & A/Z C REF LCD SEGMENT DRIVERS 200 BACKPLANE fOSC V – VTH = 1VV – INTERNAL DIGITAL GOUND LOW TEMPCO VREF COMPARATOR A/ZZI V+– 3.0V 470k 10pF 0.5mA 2mA 6.2V LCD DISPLAY 20pF V +V + 22M Ω HLDR ≈70kΩ A/Z kH FUNCTIONAL BLOCK DIAGRAM
ORDERING INFORMATION
Temp. Max V REF Part No. Package Range Tempco TC811CKW 44-PQFP 0 °C to +70°C 75 ppm/°C TC811CPL 40-Pin Plastic DIP0°C to +70°C 75 ppm/°C 3-1/2 DIGIT A/D CONVERTER WITH HOLD AND DIFFERENTIAL REFERENCE INPUTS
FEATURES
n Differential Reference Input n Display Hold Function n Fast Over-Range Recovery, Guaranteed Next Reading Accuracy n Low Temperature Drift Internal n Guaranteed Zero Reading With Zero Input n High Resolution (0.05%) and Wide Dynamic Range (72 dB) n High Impedance Differential Input 10pA Max n Direct LCD Drive – No External Components n Precision Null Detection with True Polarity at Zero n Crystal Clock Oscillator n Available in DIP, Compact Flat Package or PLCC n Convenient 9V Battery Operation with Low Power Dissipation (600µA Typical, 1mW Maximum) TYPICAL APPLICATIONS n Thermometry n Digital Meters — Voltage/Current/Power — pH Measurement — Capacitance/Inductance — Fluid Flow Rate/Viscosity — Humidity — Position n Panel Meters n LVDT Indicators n Portable Instrumentation n Digital Scales n Process Monitors n Gaussometers n Photometers TC811-7 11/5/96
3-138 TELCOM SEMICONDUCTOR, INC. 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 and a 10 12Ω input impedance. The 15µVp-p noise perfor- 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. Onboard 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 TelCom 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* Power Dissipation2 (TA ≤ 70°C) Operating Temperature Range *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. ELECTRICAL CHARACTERISTICS: VSupply = 9V, fCLOCK = 32.768kHz, and TA = 25°C, unless otherwise noted. Symbol Parameter Test Conditions Min Typ Max Unit Input — Zero Input Reading V IN = 0V – 000.0 ±000.0 +000.0 Digital VFS = 200mV Reading — Zero Reading Drift V IN = 0V, 0°C ≤ TA ≤ 70°C — 0.2 1 µV/°C — Ratiometric Reading V IN = VREF , VREF = 100mV 999 999/1000 1000 Digital Reading NL Linearity Error V FS = 200mV or 2.000V – 1 ±0.2 +1 Counts ER Roll Over Error V IN– = VIN+ ≈ 200mV – 1 ±0.2 +1 Counts eN Noise V IN = 0V, VFS = 200mV — 15 — µVP-P IL Input Leakage Current V IN = 0V — 1 10 pA CMRR Common-Mode Rejection V CM = ±1V, VIN = 0V, — 50 — µV/V VFS = 200mV 3-1/2 DIGIT A/D CONVERTER WITH HOLD AND DIFFERENTIAL REFERENCE INPUTS TC811
3-139TELCOM SEMICONDUCTOR, INC. ELECTRICAL CHARACTERISTICS: VSupply = 9V, fCLOCK = 32.768kHz, and TA = 25°C, unless otherwise noted. Symbol Parameter Test Conditions Min Typ Max Unit TC SF Scale Factor Temperature V IN = 199mV, 0°C ≤ TA ≤ 70°C — 1 5 ppm/ °C Coefficient (ext. V REF tc = 0ppm) Analog Common Section VCTC Analog Common 250K Ω from V+ to Analog Common — — — — Temperature Coefficient 0 °C ≤ TA ≤ 70°C— — — — "C" Commercial — 35 75 ppm/ °C "I" Industrial — 35 100 ppm/ °C VC Analog Common Voltage 250k Ω from V+ to Analog Common 2.7 3.05 3.35 Volts Hold Pin Input Section Input Resistance Pin 1 to Pin 37 — 70 — k Ω VIL Input Low Voltage Pin 1 — — Test +1.5 V VIH Input High Voltage Pin 1 V + – 1.5 — — V LCD Drive Section3 VSD LCD Segment Drive Voltage V + to V– = 9V 4 5 6 V P-P VSD LCD Backplane Drive Voltage V+ to V– = 9V 4 5 6 V P-P Power Supply ISUP Power Supply Current V IN = 0V, V+ to V– = 9V — — — — fOSC = 16kHz — 70 100 µA fOSC = 48kHz — 90 125 µA NOTES: 1. Input voltages may exceed supply voltages when input current is limited to 100µA. 2. Dissipation rating assumes device is mounted with all leads soldered to a printed circuit board. 3. Backplane drive is in phase with the segment drive for "segment off" 180° out of phase for "segment on." Frequency is 20 times the conversion rate. Average DC component is less than 50mV.V + NORMAL PIN CONFIGURATION 10's 100's 1000's 100's TC811CPL (40-PIN PDIP) 1's D 2 C 2 B 2 A 2 E 2 D 3 B 3 E 3 AB 4 POL (MINUS SIGN) D 1 C 1 B 1 A 1 G 1 E 1 10's OSC TEST V ANALOG COMMON CAZ OSC 2 HLDR REF V – REF C + REF C – REF V + IN V – IN VBUFF V INT V – G C A G BP (BACKPLANE) NC = NO INTERNAL CONNECTION 1 NC TC811CKW (PQFP) 12 13 14 15 17 18 G 44 43 42 41 39 3840 COM AZ BUFF INT 34 V V V 19 20 21 22 D 268 259 2410 2311 C V TEST NC NC HLDR D 2 C 2 B 2 A 2 E 2 NC OSC 2 OSC 1 REFC REFC C V + A 3 G 3 BP POL AB 4 D 1 C 1 B 1 A 1 G 1 E 1 REFV + REF IN V –IN V – PIN CONFIGURATIONS 3-1/2 DIGIT A/D CONVERTER WITH HOLD AND DIFFERENTIAL REFERENCE INPUTS TC811
3-140 TELCOM SEMICONDUCTOR, INC. 3-1/2 DIGIT A/D CONVERTER WITH HOLD AND DIFFERENTIAL REFERENCE INPUTS TC811 PIN DESCRIPTION Pin No. 40-Pin Plastic DIP Symbol Description 1 HLDR Hold pin, logic 1 holds present display reading. 2D 1 Activates the D section of the units display. 3C 1 Activates the C section of the units display. 4B 1 Activates the B section of the units display. 5A 1 Activates the A section of the units display. 6F 1 Activates the F section of the units display. 7G 1 Activates the G section of the units display. 8E 1 Activates the E section of the units display. 9D 2 Activates the D section of the tens display. 10 C 2 Activates the C section of the tens display. 11 B 2 Activates the B section of the tens display. 12 A 2 Activates the A section of the tens display. 13 F 2 Activates the F section of the tens display. 14 E 2 Activates the E section of the tens display. 15 D 3 Activates the D section of the hundreds display. 16 B 3 Activates the B section of the hundreds display. 17 F 3 Activates the F section of the hundreds display. 18 E 3 Activates the E section of the hundreds display. 19 AB 4 Activates both halves of the 1 in the thousands display. 20 POL Activates the negative polarity display. 21 BP Backplane drive output. 22 G 3 Activates the G section of the hundreds display. 23 A 3 Activates the A section of the hundreds display. 24 C 3 Activates the C section of the hundreds display. 25 G 2 Activates the G section of the tens display. 26 V – Negative power supply voltage. 27 V INT Integrator output, connection for CINT. 28 V BUFF Buffer output, connection for RINT. 29 C AZ Integrator input, connection for CAZ . 30 V IN– Analog input low. 31 V IN+ Analog input high. 32 COM Analog Common: Internal zero reference. 33 V REF – Reference input low. 34 C REF – Negative connection for reference capacitor. 35 C REF + Positive connection for reference capacitor. 36 V REF + Reference input high. 37 TEST All LCD segment test when pulled high (V +). 38 V + Positive power supply voltage. 39 OSC 2 Crystal oscillator output. 40 OSC 1 Crystal oscillator input.
3-141TELCOM SEMICONDUCTOR, INC. directly proportional to the unknown input voltage (VIN). Figure 2. Basic Dual Slope Converter
1.2 VFULL SCALE
2 CONVERSION/SEC
1 VREF tDEINT
Figure 3. Normal-Mode Rejection of Figure 1. Typical Operating Circuit
3-143TELCOM SEMICONDUCTOR, INC. power dissipation, and improve the overall performance. this indicator would reverse. all segments are turned “ON”. The display will read “-1888”. if operated with DC levels for extended periods. Figure 5. Display FONT and Segment Assignment IN– should be tied to Analog Common. noise and Auto Zero residual offsets. determined by the reference potential. Where fOSC is the crystal oscillator frequency.
3-144 TELCOM SEMICONDUCTOR, INC. 3-1/2 DIGIT A/D CONVERTER WITH HOLD AND DIFFERENTIAL REFERENCE INPUTS TC811 COMPONENT VALUE SELECTION Auto Zero Capacitor - CAZ The value of the Auto Zero capacitor (CAZ ) has some influence on system noise. A 0.47µF capacitor is recom- mended for 200mV full-scale applications where 1LSB is 100µV. A 0.10µF capacitor should be used for 2.0V full- scale applications. A capacitor with low dielectric absorption (Mylar) is required. Reference Voltage Capacitor -CREF The reference voltage used to ramp the integrator output voltage back to zero during the reference integrate cycle is stored on C REF . A 0.1µF capacitor is typical. If the application requires a sensitivity of 200mV full-scale, in- crease C REF to 1.0µF. Rollover error will be held to less than 1/2 count. A good quality, low leakage capacitor, such as Mylar, should be used. Integrating Capacitor - CINT CINT should be selected to maximize integrator output voltage swing without causing output saturation. Analog common will normally supply the differential voltage refer- ence. For this case a ±2V integrator output swing is optimum when the analog input is near full-scale. For 2 or 2.5 reading/ second (f OSC = 32kHz or 40kHz) and VFS = 200mV, a .068µF value is suggested. If a different oscillator frequency is used, C INT must be changed in inverse proportion to maintain the nominal ±2V integrator swing. An exact expression for CINT is : C INT = where: fOSC = Clock frequency at Pin 39 VFS = Full-scale input voltage R INT = Integrating resistor VINT = Desired full-scale integrator output swing C INT must have low dielectric absorption to minimize roll-over error. A polypropylene capacitor is recommended. Integrating Resistor -RINT The input buffer amplifier and integrator are designed with class A output stages which have idling currents of 6µA. The integrator and buffer can supply 1µA drive currents with negligible linearity errors. RINT is chosen to remain in the output stage linear drive region but not so large that printed circuit board leakage currents induce errors. For a 200mV full-scale, R INT should be about 180kΩ . A 2.0V full-scale requires abut 1.8MΩ . Oscillator Components The internal oscillator has been designed to operate with a quartz crystal, such as the Statek CX-1V series. Such crystals are very small and are available in a variety of standard frequencies. Note that f OSC is divided by four to generate the TC811 internal control clock. The backplane drive signal is derived by dividing f OSC by 800. To achieve maximum rejection of ac-line noise pickup, a 40kHz crystal should be used. This frequency will yield an integration period of 100msec and will reject both 50Hz and 60Hz noise. For prototyping or cost-sensitive applications a 32.768kHz watch crystal can be used, and will produce about 25dB of line-noise rejection. Other crystal frequen- cies, from 16kHz to 48kHz, can also be used. Pins 39 and 40 make up the oscillator section of the TC811. Figures 6a and 6b show some typical conversion rate component values. The LCD backplane frequency is derived by dividing the oscillator frequency by 800. Capacitive loading of the LCD may compromise display performance if the oscillator is run much over 48kHz. Reference Voltage (VREF ) A full-scale reading (2000 counts) requires the input signal be twice the reference voltage. In some applications a scale factor other than unity may exist, such as between a transducer output voltage and the required digital reading. Assume, for example, a pressure transducer output is 400mV for 2000lb/in 2. Rather than dividing the input voltage by two, the reference voltage should be set to 200mV. This permits the transducer input to be used directly. 470k 22M Ω 40.0 kHz 10pF 20pF OSC2 V+ 383940 OSC1 TC811
4000 VFS
Figure 6a. TC811 Oscillator
3-146 TELCOM SEMICONDUCTOR, INC. toward V+. Analog common source current is limited to 1µA. ficient. See TC811 Internal Voltage Reference discussion. on using TEST as a negative digital logic supply. which may cause damage to the LCD. supplying the necessary voltage reference for the TC811. Figure 9. Display Annunciator Drivers