TC811 3-1/2 Digit Analog-To-Digital Converter with Hold and Differential Reference Inputs FEATURES TYPICAL APPLICATIONS ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ 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) 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 ■ ■ ■ ■ ■ ■ ■ ORDERING INFORMATION FUNCTIONAL BLOCK DIAGRAM Temp. Range Max VREF Temp. Co. Part No. Package TC811CKW TC811CPL 44-Pin PQFP 0°C to +70°C 75 ppm/°C 40-Pin Plastic DIP 0°C to +70°C 75 ppm/°C TYPICAL SEGMENT OUTPUT + V 0.5mA SEGMENT OUTPUT LCD DISPLAY 2mA INTERNAL DIGITAL GROUND BACKPLANE TC811CPL + C REF + VREF 35 CREF CAZ RINT – VREF 36 21 – C REF V BUFF 34 33 V CINT + 28 38 LCD SEGMENT DRIVERS VINT 29 27 INTEGRATOR 10 µA ZI & A/Z ZI & A/Z – – 7 SEGMENT DECODE 200 DATA LATCH – DE (–) A/Z COMPARATOR DE (+) A/Z – V IN 7 SEGMENT DECODE 31 INT ANALOG COMMON + + + ZI + V IN 7 SEGMENT DECODE TO DIGITAL SECTION – DE (+) 32 30 + DE (–) LOW TEMPCO VREF TENS UNITS TO SWITCH DRIVERS FROM COMPARATOR OUTPUT CLOCK V+– 3.0V 26 – V 38 ≈70kΩ fOSC 4 AZ & DE (±) INT HUNDREDS THOUSANDS CONTROL LOGIC INTERNAL DIGITAL GOUND 39 22MΩ TEST 1 OSC 2 + 500Ω VTH = 1V 26 40 OSC 1 V 6.2V V– HLDR 470k V © 2001 Microchip Technology Inc. DS21472A + 10pF 20pF V + TC811-7 11/5/96 3-1/2 Digit Analog-To-Digital Converter with Hold and Differential Reference Inputs TC811 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. Compact, hand held multimeter designs benefit from the Microchip 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. 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. On-board oscillator, precision voltage reference and display segment and backplane drivers sim- 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 ...................................................... TEST to V+ Power Dissipation2 (TA ≤ 70°C) 44-Pin Flat Package .........................................1.00W 40-Pin Plastic DIP ............................................. 1.23W Operating Temperature Range Commercial Package (C) ...................... 0°C to +70°C Industrial Package (I) ........................ – 25°C to +85°C Storage Temperature Range ................ – 65°C to +150°C Lead Temperature (Soldering, 10 sec) ................. +300°C *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 permanent 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 — Zero Input Reading — — Zero Reading Drift Ratiometric Reading VIN = 0V VFS = 200mV VIN = 0V, 0°C ≤ TA ≤ 70°C VIN = VREF, VREF = 100mV NL ER eN IL CMRR Linearity Error Roll Over Error Noise Input Leakage Current Common-Mode Rejection Min Typ Max – 000.0 ±000.0 +000.0 — 999 0.2 999/1000 1 1000 –1 –1 — — — ±0.2 ±0.2 15 1 50 +1 +1 — 10 — Unit Input TC811-7 11/5/96 VFS = 200mV or 2.000V VIN– = VIN+ ≈ 200mV VIN = 0V, VFS = 200mV VIN = 0V VCM = ±1V, VIN = 0V, VFS = 200mV 2 Digital Reading µV/°C Digital Reading Counts Counts µVP-P pA µV/V © 2001 Microchip Technology Inc. DS21472A 3-1/2 Digit Analog-To-Digital Converter with Hold and Differential Reference Inputs TC811 ELECTRICAL CHARACTERISTICS: VSupply = 9V, fCLOCK = 32.768kHz, and TA = 25°C, unless otherwise noted. Symbol Parameter Test Conditions Min Typ Max Unit TCSF Scale Factor Temperature Coefficient VIN = 199mV, 0°C ≤ TA ≤ 70°C (ext. VREF tc = 0ppm) — 1 5 ppm/°C 250KΩ from V+ to Analog Common 0°C ≤ TA ≤ 70°C "C" Commercial "I" Industrial 250kΩ from V+ to Analog Common — — — — 2.7 — — 35 35 3.05 — — 75 100 3.35 — — ppm/°C ppm/°C Volts Pin 1 to Pin 37 Pin 1 Pin 1 — — V+ – 1.5 70 — — — Test +1.5 — kΩ V V V + to V – = 9V V+ to V– = 9V 4 4 5 5 6 6 VP-P VP-P VIN = 0V, V + to V – = 9V — — — — fOSC = 16kHz — 70 100 µA fOSC = 48kHz — 90 125 µA Analog Common Section VCTC Analog Common Temperature Coefficient VC Analog Common Voltage Hold Pin Input Section VIL VIH Input Resistance Input Low Voltage Input High Voltage LCD Drive Section3 VSD VSD LCD Segment Drive Voltage LCD Backplane Drive Voltage Power Supply ISUP Power Supply Current 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. 6 35 G1 7 34 E1 8 33 D2 9 C2 10 31 B2 11 30 A2 12 29 F2 13 28 VBUFF E2 14 D3 15 26 V– B3 16 25 G2 TC811CPL (40-PIN PDIP) 32 27 F3 17 24 C3 18 23 A3 AB4 19 22 G3 POL 20 (MINUS SIGN) 21 BP (BACKPLANE) 1000's CAZ V BUFF V INT V– COM VIN + VIN – 33 NC NC 2 32 G 2 TEST 3 31 C 3 V+ 4 30 A 3 29 G 3 TC811CKW (PQFP) OSC 2 6 10's E3 NC 1 NC 5 V INT 34 28 BP OSC 1 7 27 POL HLDR 8 26 AB 4 D1 9 25 E3 C 1 10 24 F3 B 1 11 23 B3 12 13 14 15 16 17 18 19 20 21 22 D3 F1 35 36 E2 36 37 F2 37 5 38 A2 100's 4 A1 41 40 39 B2 10's B1 42 C2 1's 44 43 TEST V REF+ CREF+ CREF– VREF– ANALOG COMMON V IN+ V IN– CAZ E1 3 D2 C1 40 OSC 1 NORMAL PIN CONFIGURATION 39 OSC 2 38 V + G1 D1 2 F1 1 A1 HLDR VREF+ + CREF CREF – VREF– PIN CONFIGURATIONS 100's NC = NO INTERNAL CONNECTION © 2001 Microchip Technology Inc. DS21472A 3 TC811-7 11/5/96 3-1/2 Digit Analog-To-Digital Converter with Hold and Differential Reference Inputs TC811 PIN DESCRIPTION Pin No. 40-Pin Plastic DIP 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 TC811-7 11/5/96 Symbol HLDR D1 C1 B1 A1 F1 G1 E1 D2 C2 B2 A2 F2 E2 D3 B3 F3 E3 AB4 POL BP G3 A3 C3 G2 V– VINT VBUFF CAZ VIN– + VIN COM – VREF – CREF + CREF + VREF TEST V+ OSC2 OSC1 Description Hold pin, logic 1 holds present display reading. Activates the D section of the units display. Activates the C section of the units display. Activates the B section of the units display. Activates the A section of the units display. Activates the F section of the units display. Activates the G section of the units display. Activates the E section of the units display. Activates the D section of the tens display. Activates the C section of the tens display. Activates the B section of the tens display. Activates the A section of the tens display. Activates the F section of the tens display. Activates the E section of the tens display. Activates the D section of the hundreds display. Activates the B section of the hundreds display. Activates the F section of the hundreds display. Activates the E section of the hundreds display. Activates both halves of the 1 in the thousands display. Activates the negative polarity display. Backplane drive output. Activates the G section of the hundreds display. Activates the A section of the hundreds display. Activates the C section of the hundreds display. Activates the G section of the tens display. Negative power supply voltage. Integrator output, connection for CINT. Buffer output, connection for RINT. Integrator input, connection for CAZ. Analog input low. Analog input high. Analog Common: Internal zero reference. Reference input low. Negative connection for reference capacitor. Positive connection for reference capacitor. Reference input high. All LCD segment test when pulled high (V+). Positive power supply voltage. Crystal oscillator output. Crystal oscillator input. 4 © 2001 Microchip Technology Inc. DS21472A 3-1/2 Digit Analog-To-Digital Converter with Hold and Differential Reference Inputs TC811 0.1µF 0.01µF – 30 V IN TC811 LCD 180kΩ 0.068µF 0.47 µF 29 POL BP 27 V+ + 21 MINUS SIGN SWITCH DRIVER 1 HLDR 36 + VREF – 33 V REF 26 V– OSC1 39 470k V+ PHASE CONTROL CONTROL LOGIC POLARITY CONTROL REF VOLTAGE + 9V CLOCK 10k Ω 2 CONVERSION/SEC 40 TO ANALOG COMMON (PIN 32) 22MΩ 20pF +/– 38 240kΩ VINT OSC2 BACKPLANE COMPARATOR – + 20 VBUFF CAZ INTEGRATOR – 9–19 SEGMENT 22–25 DRIVE 32 ANALOG COMMON 28 C ANALOG INPUT SIGNAL VIN VIN FIXED SIGNAL INTEGRATE TIME 10pF V+ COUNTER DISPLAY INTEGRATOR OUTPUT 1MΩ + ANALOG INPUT – 33 C 34 REF 35 + C REF 31 + V IN ≈ VFULL SCALE ≈ 1.2 VFULL SCALE VARIABLE REFERENCE INTEGRATE TIME Figure 2. Basic Dual Slope Converter Figure 1. Typical Operating Circuit GENERAL THEORY OF OPERATION Dual-Slope Conversion Principles NORMAL MODE REJECTION (dB) 30 (All Pin Designations Refer to 40-Pin DIP Package) The TC811 is a dual slope, integrating analog-to-digital converter. An understanding of the dual slope conversion technique will aid the user in following the detailed TC811 theory of operation following this section. A conventional dual slope converter measurement cycle has two distinct phases: 1) Input Signal Integration 2) Reference Voltage Integration (Deintegration) Referring to Figure 2, the unknown input signal to be converted is integrated from zero for a fixed time period (TINT), measured by counting clock pulses. A constant reference voltage of the opposite polarity is then integrated until the integrator output voltage returns to zero. The reference integration (deintegration) time (TDEINT) is then directly proportional to the unknown input voltage (VIN). In a simple dual slope converter, a complete conversion requires the integrator output to “ramp-up” from zero and “ramp-down” back to zero. A simple mathematical equation relates the input signal, reference voltage and integration time: tINT 1 VREF tDEINT VIN(t) dt = RINT CINT 0 RINT CINT 20 10 T = MEASUREMENT PERIOD 0 0.1/T 1/T INPUT FREQUENCY 10/T Figure 3. Normal-Mode Rejection of Dual Slope Converter For a constant VINT: VIN = VREF [ ] tDEINT tINT ∫ where: VREF = Reference voltage tINT = Integration Time tDEINT = Deintegration Time © 2001 Microchip Technology Inc. DS21472A 5 TC811-7 11/5/96 3-1/2 Digit Analog-To-Digital Converter with Hold and Differential Reference Inputs TC811 Accuracy in a dual slope converter is unrelated to the integrating resistor and capacitor values as long as they are stable during a measurement cycle. An inherent benefit of the dual slope technique is noise immunity. Noise spikes are integrated or averaged to zero during the integration periods, making integration ADCs immune to the large conversion errors that plague successive approximation converters in high noise environments. Interfering signals, with frequency components at multiples of the averaging (integrating) period, will be attenuated. (see Figure 3). Integrating ADCs commonly operate with the signal integration period set to a multiple of the 50/60Hz power line period. 1000 INT 11–140 ZI AZ 910–2900 4000 THEORY OF OPERATION Analog Section Figure 4a. Conversion Timing During Normal Operation In addition to the basic integrate and deintegrate dualslope cycles discussed above, the TC811 design incorporates an “Integrator Output Zero” cycle and an “Auto Zero” cycle. These additional cycles ensure the integrator starts at 0V (even after a severe overrange conversion) and that all offset voltage errors (buffer amplifier, integrator and comparator) are removed from the conversion. A true digital zero reading is assured without any external adjustments. A complete conversion consists of four distinct phases: (1) (2) (3) (4) INT 1000 2001–2090 DE-INT 31–640 ZI AZ 300–910 4000 Integrator Output Zero Cycle Auto Zero Cycle Signal Integrate Cycle Reference Deintegrate Cycle Figure 4b. Conversion Timing During Overrange Operation is typically 10 to 15µV. The Auto Zero duration is from 910 to 2,900 counts for non-over-range conversions and from 300 to 910 counts for overrange conversions. Integrator Output Zero Cycle This phase guarantees that the integrator output is at zero volts before the system zero phase is entered, ensuring that the true system offset voltages will be compensated for even after an overrange conversion. The duration of this phase is variable, being a function of the number of counts (clock cycles) required for deintegration. The Integrator Output Zero cycle will last from 11 to 140 counts for non-over-range conversions and from 31 to 640 counts for overrange conversions. Signal Integration Cycle Upon completion of the Auto Zero cycle, the Auto Zero loop is opened and the internal differential inputs connect to VIN+ and VIN–. The differential input signal is then integrated for a fixed time period which, in the TC811 is 1000 counts (4000 clock periods). The externally set clock frequency is divided by four before clocking the internal counters. The integration time period is: Auto Zero Cycle During the Auto Zero cycle, the differential input signal is disconnected from the measurement circuit by opening internal analog switches and the internal nodes are shorted to Analog Common (0V ref.) to establish a zero input condition. Additional analog switches close a feedback loop around the integrator and comparator to permit comparator offset voltage error compensation. A voltage established on CAZ then compensates for internal device offset voltages during the measurement cycle. The Auto Zero cycle residual TC811-7 11/5/96 1–2000 DE-INT TINT = 4000 fOSC The differential input voltage must be within the device common-mode range when the converter and measured system share the same power supply common (ground). If the converter and measured system do not share the same power supply common, as in battery powered applications, VIN– should be tied to Analog Common. 6 © 2001 Microchip Technology Inc. DS21472A 3-1/2 Digit Analog-To-Digital Converter with Hold and Differential Reference Inputs TC811 Polarity is determined at the end of signal integration phase. The sign bit is a “true polarity” indication in that signals less than 1 LSB are correctly determined. This allows precision null detection which is limited only by device noise and Auto Zero residual offsets. power dissipation, and improve the overall performance. (see Oscillator Components) Digital Section The TC811 contains all the segment drivers necessary to directly drive a 3-1/2 digit liquid crystal display (LCD). An LCD backplane driver is included. The backplane frequency is the external clock frequency divided by 800. For three conversions/second the backplane frequency is 60Hz with a 5V nominal amplitude. When a segment driver is in phase with the backplane signal the segment of “OFF”. An out of phase segment drive signal causes the segment to be “ON” or visible. This AC drive configuration results in negligible DC voltage across each LCD segment. This insures long LCD display life. The polarity segment driver is “ON” for negative analog inputs. If VIN+ and VIN– are reversed then this indicator would reverse. Reference Integrate (Deintegrate) Cycle The reference capacitor, which was charged during the Auto Zero cycle, is connected to the input of the integrating amplifier. The internal sign logic insures that the polarity of the reference voltage is always connected in the phase which is opposite to that of the input voltage. This causes the integrator to ramp back to zero at a constant rate which is determined by the reference potential. The amount of time required (TDEINT) for the integrating amplifier to reach zero is directly proportional to the amplitude of the voltage that was put on the integrating capacitor (VINT) during the integration cycle: TDEINT = TEST Function (TEST) RINT CINT VINT VREF On the TC811, when TEST is pulled to a logical “HIGH”, all segments are turned “ON”. The display will read “-1888”. During this mode the LCD segments have a constant DC voltage impressed. Do not leave the display in this mode for more than several minutes. LCD displays may be destroyed if operated with DC levels for extended periods. The display FONT and segment drive assignment are shown in Figure 5. The digital reading displayed Is: + Digital Count = 1000 – VIN – VIN VREF The oscillator frequency is divided by 4 prior to clocking the internal decade counters. The four phase measurement cycle takes a total of 4000 counts or 16000 clock pulses. The 4000 count cycle is independent of input signal magnitude or polarity. Each phase of the measurement cycle has the following length: DISPLAY FONT 1) Auto Zero: 300 to 2900 Counts 2) Signal Integrate: 1000 Counts 1000's 100's 10's 1's This time period is fixed. The integration period is: TINT = 4000 = 1000 Counts fOSC Figure 5. Display FONT and Segment Assignment Where fOSC is the crystal oscillator frequency. 3) Reference Integrate: 0 to 2000 Counts 4) Integrator Output Zero: 11 to 640 Counts HOLD Reading Input (HLDR) When HLDR is at a logic “HI” the latch will not be updated. Conversions will continue but will not be updated until HLDR is returned to “LOW”. To continuously update the display, connect HLDR to ground or leave it open. This input is CMOS compatible and has an internal resistance of 70kΩ (typical) tied to TEST. The TC811 can replace the ICL7106/26/36 in circuits which require both the hold function and a differential reference. The TC811 offers a greatly improved internal reference temperature coefficient, which can often eliminate the need for an external reference. Some minor component changes are required to upgrade existing designs, reduce © 2001 Microchip Technology Inc. DS21472A 7 TC811-7 11/5/96 3-1/2 Digit Analog-To-Digital Converter with Hold and Differential Reference Inputs TC811 Oscillator Components COMPONENT VALUE SELECTION Auto Zero Capacitor - CAZ 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 fOSC is divided by four to generate the TC811 internal control clock. The backplane drive signal is derived by dividing fOSC 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 frequencies, 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. The value of the Auto Zero capacitor (CAZ) has some influence on system noise. A 0.47µF capacitor is recommended for 200mV full-scale applications where 1LSB is 100µV. A 0.10µF capacitor should be used for 2.0V fullscale 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 CREF. A 0.1µF capacitor is typical. If the application requires a sensitivity of 200mV full-scale, increase CREF 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 reference. 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 (fOSC = 32kHz or 40kHz) and VFS = 200mV, a .068µF value is suggested. If a different oscillator frequency is used, CINT must be changed in inverse proportion to maintain the nominal ±2V integrator swing. An exact expression for CINT is : 4000 VFS CINT = VINT RINT fOSC 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/in2. 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. where: fOSC = Clock frequency at Pin 39 VFS = Full-scale input voltage RINT = Integrating resistor VINT = Desired full-scale integrator output swing TC811 CINT must have low dielectric absorption to minimize roll-over error. A polypropylene capacitor is recommended. OSC1 40 22MΩ OSC2 39 V+ 38 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, RINT should be about 180kΩ. A 2.0V full-scale requires abut 1.8MΩ. TC811-7 11/5/96 40.0 kHz 10pF 470k 9V 20pF + Figure 6a. TC811 Oscillator 8 © 2001 Microchip Technology Inc. DS21472A 3-1/2 Digit Analog-To-Digital Converter with Hold and Differential Reference Inputs TC811 Oscillator Freq. (kHz) facing with sensors such as load cells and temperature sensors. The TC811 is ideally suited to applications in handheld multimeters, panel meters, and portable instrumentation. The reference voltage can be generated anywhere within the V+ to V– power supply range. To prevent rollover type errors from being induced by large common-mode voltages, CREF should be large compared to stray node capacitance. A 0.1µF capacitor is a typical value. The TC811 offers a significantly improved Analog Common temperature coefficient. This provides a very stable voltage suitable for use as a voltage reference. The temperature coefficient of Analog Common is typically 35ppm/°C. Full-Scale Voltage (VFS) 200mV 2.0V RINT CINT RINT CINT 32.768 40 180k 150k 0.068µF 0.068µF 1.8M 1.5M 0.068µF 0.068µF Figure 6b. DEVICE PIN FUNCTIONAL DESCRIPTION + Differential Signal Inputs (VIN (Pin 31), – VIN (Pin 30)) The TC811 is designed with true differential inputs and accepts input signals within the input stage common mode voltage range (VCM). The typical range is V+ – 1.0 to V– + 1.5V. Common-mode voltages are removed from the system when the TC811 operates from a battery or floating power source (isolated from measured system) and VIN– is connected to Analog Common. (see Figure 8) In systems where common-mode voltages exist, the 86dB common-mode rejection ratio minimizes error. Common-mode voltages do, however, affect the integrator output level. A worse case condition exists if a large positive VCM exists in conjunction with a full-scale negative differential signal. The negative signal drives the integrator output positive along with VCM (Figure 8). For such applications the integrator output swing can be reduced below the recommended 2.0V full-scale swing. The integrator output will swing within 0.3V of V+ or V– without increased linearity error. + CI INPUT BUFFER + RI + – – VIN VI + INTEGRATOR – TI VI = V CM – VIN RI CI Where: 4000 T I = INTEGRATION TIME = f OSC [ VCM [ C I = INTEGRATION CAPACITOR R I = INTEGRATION RESISTOR – Reference (VREF (Pin 36), VREF (Pin 33)) Figure 8. Common-Mode Voltage Reduces Available Integrator Swing. (VCOM ≠ VIN) Unlike the ICL7116, the TC811 has a differential reference as well as the “hold” function. The differential reference inputs permit ratiometric measurements and simplify inter- SEGMENT DRIVE 10pF MEASURED SYSTEM VBUF V+ V+ V– V– GND LCD DISPLAY CAZ VINT POL BP OSC1 20MΩ TC811 V+ 470k V+ V – GND POWER SOURCE 40kHZ 20 pF OSC2 V– ANALOG – + + COMMON VREF VREF V V+ + 9V – Figure 7. Common-Mode Voltage Removed in Battery Operation With VIN = Analog Common © 2001 Microchip Technology Inc. DS21472A 9 TC811-7 11/5/96 3-1/2 Digit Analog-To-Digital Converter with Hold and Differential Reference Inputs TC811 Analog Common (Pin 32) APPLICATIONS INFORMATION Decimal Point and Annunciator Drive The Analog Common pin is set at a voltage potential approximately 3.0V below V+. This potential is guaranteed to be between 2.70V and 3.35V below V+. Analog common is tied internally to an N channel FET capable of sinking 100µA. This FET will hold the common line at 3.0V below V+ should an external load attempt to pull the common line toward V+. Analog common source current is limited to 1µA. Analog common is therefore easily pulled to a more negative voltage (i.e. below V+ – 3.0V). + – The TC811 connects the internal VIN and VIN inputs to Analog Common during the Auto Zero cycle. During the – is connected to Analog Comreference integrate phase VIN – mon. If VIN is not externally connected to Analog Common, a common-mode voltage exists. This is rejected by the converter’s 86dB common-mode rejection ratio. In battery – powered applications, Analog Common and VIN are usually connected, removing common-mode voltage concerns. In – systems where VIN is connected to the power supply ground or to a given voltage, Analog Common should be connected – to VIN . The Analog Common pin serves to set the analog section reference or common point. The TC811 is specifically designed to operate from a battery or in any measurement system where input signals are not referenced (float) with respect to the TC811 power source. The Analog Common potential of V+ – 3.0V gives a 7V end of battery life voltage. The analog common potential has a voltage coefficient of 0.001%/%. With a sufficiently high total supply voltage (V+ – V– > 7.0V), Analog Common is a very stable potential with excellent temperature stability (typically 35ppm/°C). This potential can be used to generate the TC811 reference voltage. An external voltage reference will be unnecessary in most cases because of the 35ppm/°C temperature coefficient. See TC811 Internal Voltage Reference discussion. The TEST pin is connected to the internally generated digital logic supply ground through a 500Ω resistor. The TEST pin may be used as the negative supply for external CMOS gate segment drivers. LCD display annunciators for decimal points, low battery indication, or function indication may be added without adding an additional supply. No more than 1mA should be supplied by the TEST pin. The TEST pin potential is approximately 5V below V+. Internal Voltage Reference The TC811 Analog Common voltage temperature stability has been significantly improved. This improved device can be used to upgrade old systems and design new systems without external voltage references. External R and C values do not need to be changed, however, noise performance will be improved by increasing CAZ (See Auto Zero Capacitor section). Figure 10 shows Analog Common supplying the necessary voltage reference for the TC811. V+ V+ 4049 TC811 GND TEST TO LCD BACKPLANE V+ V+ TEST (Pin 37) The TEST pin potential is 5V less the V+. TEST may be used as the negative power supply connection when interfacing the TC811 to external CMOS logic. The TEST pin is tied to the internally generated negative logic supply through a 500Ω resistor. The TEST pin may be used to sink up to 1mA. See the applications section for additional information on using TEST as a negative digital logic supply. If TEST is pulled “HIGH” (V+), all segments plus the minus sign will be activated. Do not operate in this mode for more than several minutes, because when TEST is pulled to V+, the LCD Segments are impressed with a DC voltage which may cause damage to the LCD. TC811-7 11/5/96 TO LCD DECIMAL POINT BP TC811 BP TO LCD DECIMAL POINTS DECIMAL POINT SELECT HDLR TO "HOLD" ANNUNCIATOR TEST 4030 GND Figure 9. Display Annunciator Drivers 10 © 2001 Microchip Technology Inc. DS21472A 3-1/2 Digit Analog-To-Digital Converter with Hold and Differential Reference Inputs TC811 Liquid Crystal Display Sources 9V Several LCD manufactures supply standard LCD displays to interface with the TC811 3-1/2 digit analog-to-digital converter. Manufacturer Address/Phone Crystaloid Electronics 5282 Hudson Dr., Hudson, OH 44236 216-655-2429 770 Airport Blvd., Burlingame, CA 94010 415-347-9916 3415 Kashikawa St., Torrence, CA 90505 212-534-0360 612 E. Lake St., Lake Mills, WI 53551 414-648-2361 AND EPSON Hamlin, Inc. *NOTE: + 38 26 V+ V– Representative Part Numbers* 240kΩ TC811 C5335, H5535, T5135, SX440 + VREF 36 10kΩ VREF FE 0801, FE 0203 – VREF 33 ANALOG 32 COMMON LD-B709BZ LD-H7992AZ SET VREF = 1/2 VFULL SCALE 3902, 3933, 3903 Figure 10. TC811 Internal Voltage Reference Connection Contact LCD manufacturer for full product listing/specifications. Oscillator Crystal Source Manufacturer Address/Phone STATEK 512 N-Main Orange, CA 92668 714-639-7810 R STANDARD Representative Part Numbers CX-1V 40.0 TC811 LCD R UNKNOWN – V IN ANALOG COMMON The TC811 true differential input and differential reference make ratiometric readings possible. In ratiometric operation, an unknown resistance is measured with respect to a known standard resistance. No accurately defined reference voltage is needed. The unknown resistance is put in series with a known standard and a current is passed through the pair (Figure 11). The voltage developed across the unknown is applied to the input and the voltage across the known resistor applied to the reference input. If the unknown equals the standard, the input voltage will equal the reference voltage and the display will read 1000. The displayed reading can be determined from the following expression: RUNKNOWN RSTANDARD REF + V IN Ratiometric Resistance Measurements Displayed reading = + V + HLDR VREF V– Figure 11. Low Parts Count Ratio Metric Resistance Measurement x 1000 The display will overrange for R UNKNOWN ≥ 2 X RSTANDARD. © 2001 Microchip Technology Inc. DS21472A 11 TC811-7 11/5/96 3-1/2 Digit Analog-To-Digital Converter with Hold and Differential Reference Inputs TC811 + 160 kΩ 1N4148 SENSOR 300 kΩ 300 kΩ R1 50 kΩ 5.6 kΩ V+ – VIN 160 kΩ V– 1N914 TC811 R1 20 kΩ + VIN 0.7%/°C PTC R3 R2 20 kΩ V– TC811 + VREF – VREF – VREF COMMON V+ – VIN + VIN VFS = 200 MV + VREF R2 50 kΩ 9V + 9V HLDR COMMON V+ Figure 12. Temperature Sensor HLDR V+ Figure 13. Positive Temperature Coefficient Resistor Temperature Sensor PACKAGE DIMENSIONS 40-Pin Plastic DIP PIN 1 .555 (14.10) .530 (13.46) 2.065 (52.45) 2.027 (51.49) .610 (15.49) .590 (14.99) .200 (5.08) .140 (3.56) .040 (1.02) .020 (0.51) .150 (3.81) .115 (2.92) .110 (2.79) .090 (2.29) .070 (1.78) .045 (1.14) .015 (0.38) .008 (0.20) 3° MIN. .700 (17.78) .610 (15.50) .022 (0.56) .015 (0.38) Dimensions: inches (mm) TC811-7 11/5/96 12 © 2001 Microchip Technology Inc. DS21472A 3-1/2 Digit Analog-To-Digital Converter with Hold and Differential Reference Inputs TC811 PACKAGE DIMENSIONS (CONT.) 44-Pin QFP 7° MAX. .009 (0.23) .005 (0.13) PIN 1 .018 (0.45) .012 (0.30) .041 (1.03) .026 (0.65) .398 (10.10) .390 (9.90) .557 (14.15) .537 (13.65) .031 (0.80) TYP. .010 (0.25) TYP. .398 (10.10) .390 (9.90) .083 (2.10) .075 (1.90) .557 (14.15) .537 (13.65) .096 (2.45) MAX. Dimensions: inches (mm) © 2001 Microchip Technology Inc. DS21472A 13 TC811-7 11/5/96 3-1/2 Digit Analog-To-Digital Converter with Hold and Differential Reference Inputs TC811 WORLDWIDE SALES AND SERVICE AMERICAS New York ASIA/PACIFIC (continued) Corporate Office 150 Motor Parkway, Suite 202 Hauppauge, NY 11788 Tel: 631-273-5305 Fax: 631-273-5335 Singapore 2355 West Chandler Blvd. Chandler, AZ 85224-6199 Tel: 480-792-7200 Fax: 480-792-7277 Technical Support: 480-792-7627 Web Address: http://www.microchip.com Rocky Mountain 2355 West Chandler Blvd. Chandler, AZ 85224-6199 Tel: 480-792-7966 Fax: 480-792-7456 San Jose Microchip Technology Inc. 2107 North First Street, Suite 590 San Jose, CA 95131 Tel: 408-436-7950 Fax: 408-436-7955 Microchip Technology Singapore Pte Ltd. 200 Middle Road #07-02 Prime Centre Singapore, 188980 Tel: 65-334-8870 Fax: 65-334-8850 Taiwan Atlanta 6285 Northam Drive, Suite 108 Mississauga, Ontario L4V 1X5, Canada Tel: 905-673-0699 Fax: 905-673-6509 500 Sugar Mill Road, Suite 200B Atlanta, GA 30350 Tel: 770-640-0034 Fax: 770-640-0307 Microchip Technology Taiwan 11F-3, No. 207 Tung Hua North Road Taipei, 105, Taiwan Tel: 886-2-2717-7175 Fax: 886-2-2545-0139 ASIA/PACIFIC Austin EUROPE China - Beijing Australia Analog Product Sales 8303 MoPac Expressway North Suite A-201 Austin, TX 78759 Tel: 512-345-2030 Fax: 512-345-6085 Boston 2 Lan Drive, Suite 120 Westford, MA 01886 Tel: 978-692-3848 Fax: 978-692-3821 Boston Analog Product Sales Unit A-8-1 Millbrook Tarry Condominium 97 Lowell Road Concord, MA 01742 Tel: 978-371-6400 Fax: 978-371-0050 Toronto Microchip Technology Beijing Office Unit 915 New China Hong Kong Manhattan Bldg. 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No licenses are conveyed, implicitly or otherwise, except as maybe explicitly expressed herein, under any intellectual property rights. The Microchip logo and name are registered trademarks of Microchip Technology Inc. in the U.S.A. and other countries. All rights reserved. All other trademarks mentioned herein are the property of their respective companies. TC811-7 11/5/96 14 © 2001 Microchip Technology Inc. DS21472A