AME811

Analog Microelectronics, Inc. AME811/AME811A/AME811R 3-1/2 Digit A/D Converter - Low Power With HOLD And Differential Reference Inputs n Key Features l 100µV Resolution l High Impedance Differential Inputs l Differential Reference l Drive LCD Directly l Three New Convenient Features (AME811A Only) l Low-Battery Indication l Integration Status Indication l De-Integration Status Indication n General Description The AME811 family are high performance, low power. 3-1/2 digit, dual-slope integrating A/D converters, with on-chip display drivers. The AME811 is designed for a single battery operated system, will drive non-multiplexed LCD display directly. These A/D converters are inherently versatile and accurate. They are immune to the high noise environments. The true differential high impedance inputs and differential reference are very useful for making ratiometric measurement, such as resistance, strain gauge and bridge transducers. The built-in auto-zero feature automatically corrects the system offset without any external adjustments. Low-battery flag, integration and de-integration status flags are three additional features which are available in the 44-pin package, AME811ACKW. n Applications l Digital multimeter l pH meter l Capacitance meter l Thermometer l Digital Panel meter l Photometer n Typical Operating Circuit * For the operating circuit of the reverse-pins version, please refer to pin configuration on page 4 and pin description on page 5 & 6. 0.1 35 34 C REF+ C REF31 30 32 IN HI IN LO CO M 2-19 SEGMENT 22-25 DRIVE PO L BP V+ 20 21 38 24K BUF A/Z V REF+ 36 V REF 9V 1K MINUS SIGN BACKPLANE D RIVE LCD DISPLAY 1M AN ALOG INPUT 0.01 28 47K 0.22 0.47 29 27 INT O SC 2 OSC 1 39 40 20M V REF- 33 V- 26 TO ANALO G COM MON (P32) V+ 470K V+ 20pF 40KHz 10pF FULL SCALE IN PUT 200.0mV V REF 100.0mV 1 Analog Microelectronics, Inc. AME811/AME811A/AME811R 3-1/2 Digit A/D Converter - Low Power With HOLD And Differential Reference Inputs n Absolute Maximum Ratings AME811 Supply Voltage (V+ to V-) Analog Input Voltage (Either inputs) Reference Input Voltage (Either inputs) Clock Input Power Dis sipation Operating Temperature Storage Temperature Lead Temperature (Soldering 60 seconds) 12V V+ to VV+ to VTest to V+ 800mW 0 o C to 70 oC -55 o C to 150 oC 300 o C Static sensitive device. Unused devices must be stored in the conductive material. Protect device from static discharge and static field. Stresses exceed the above Absolute Maximum Ratings may cause permanent damage to the device. Exposure to Absolute Maximum Rating Conditions for extended periods may affect the reliability of the device. n Ordering Information Part Number AME811CPL AME811RCPL AME811ACKW Display LCD LCD LCD Marking AME811CPL YYWW AME811RCPL YYWW AME811ACKW YYWW Package 40 Pin PDIP 40 Pin PDIP 44 Pin PQFP Pin Layout Normal Reverse Normal Temp.Range 0oC to 70oC 0oC to 70oC 0oC to 70oC 2 Analog Microelectronics, Inc. AME811/AME811A/AME811R 3-1/2 Digit A/D Converter - Low Power With HOLD And Differential Reference Inputs n Electrical Characteristics Parameter Zero Input Reading Ratiometric Reading Roll-Over Error (Difference in Reading for Equal Positive and Negative Reading Near Full-Scale) Linearity (Max. Deviation From Best Straight Line Fit) Common-Mode Rejection Ratio Noise (Pk-Pk Value Not Exceeded 95% of Time) Leakage Current at Input Zero Reading Drift Analog Common Voltage (With respect to V+) o Unless otherwise noted, AME811 is specified at TA = 25 C, fclock = 48KHz. Supply voltage = 9V (V+ to V-) Conditions Vin = 0V Full-Scale = 200.0mV Vin = Vref = 100.0mV Min -0 Typ w0 Max Unit +0 Digital Reading 999 999/1000 1000 Digital Reading –0.2 +1 Counts -Vin = +Vin ≈ 200.0mV -1 Full-Scale = 200.0mV Vcm = –1V, Vin =0V Full-Scale = 200.0mV Vin = 0V Full-Scale = 200.0mV Vin = 0V Vin = 0V, 0 C to 70 C 25KΩ Between Common and V+ o o -1 –0.2 50 15 1 0.2 +1 Counts µV/V µV 10 1 3.2 pA µV/ C V o o 2.8 3 Temp. Coeff. of Analog 25KΩ Between Common (With respect to V+) Common and V+ Low Battery Flag Test Pin Voltage LCD Segment Drive Voltage Backplane Drive Voltage 0 C m TA m 70 C V+ to VWith respect to V+ V+ to V- = 9V V+ to V- = 9V o o 50 6.3 4 4 4 7.0 5 5 5 75 7.7 6 6 6 ppm/ C V V V V Notes: 1. Input voltage may exceed the supply voltages provided the input current is limited to ±100µA. 2. Dissipation rating assumes a device is mounted with all leads soldered to printed circuit board. 3 Analog Microelectronics, Inc. AME811/AME811A/AME811R 3-1/2 Digit A/D Converter - Low Power With HOLD And Differential Reference Inputs n Pin Configurations 4 Analog Microelectronics, Inc. AME811/AME811A/AME811R 3-1/2 Digit A/D Converter - Low Power With HOLD And Differential Reference Inputs n Pin Description 40-pin DIP 40-pin DIP 44-pin PQFP Symbol Pin Number (Reverse) Pin Number 1 (40) 8 HOLD 2 (39) 9 D1 3 (38) 10 C1 4 (37) 11 B1 5 (36) 12 A1 6 (35) 13 F1 7 (34) 14 G1 8 (33) 15 E1 9 (32) 16 D2 10 (31) 17 C2 11 (30) 18 B2 12 (29) 19 A2 13 (28) 20 F2 14 (27) 21 E2 15 (26) 22 D3 16 (25) 23 B3 17 (24) 24 F3 18 (23) 25 E3 19 (22) 26 AB4 20 (21) 27 POL 21 (20) 28 BP 22 (19) 29 G3 23 (18) 30 A3 24 (17) 31 C3 25 (16) 32 G2 ¢w 33 LB 26 (15) 34 V27 (14) 35 INT 28 29 30 31 32 33 (13) (12) (11) (10) (9) (8) 36 37 38 39 40 41 BUF A/Z INLO INHI COM VREFDescription HOLD pin, Logic 1, Holds Display Units-digit D-segment driver Units-digit C-segment driver Units-digit B-segment driver Units-digit A-segment driver Units-digit F-segment driver Units-digit G-segment driver Units-digit E-segment driver Tens-digit D-segment driver Tens-digit C-segment driver Tens-digit B-segment driver Tens-digit A-segment driver Tens-digit F-segment driver Tens-digit E-segment driver Hundreds-digit D-segment driver Hundreds-digit B-segment driver Hundreds-digit F-segment driver Hundreds-digit E-segment driver Thousands-digit, B&C segments driver Negative-polarity driver LCD backplane driver Hundreds-digit G-segment driver Hundreds-digit A-segment driver Hundreds-digit C-segment driver Tens-digit G-segment driver Low-battery flag segment driver Negative power supply voltage Integrator output. Connection point for integration capacitor. Integrator resistor connection-point. Auto-zero capacitor connection-point Analog-input low Analog-input high Analog-common Analog-reference input, negative terminal 5 Analog Microelectronics, Inc. AME811/AME811A/AME811R 3-1/2 Digit A/D Converter - Low Power With HOLD And Differential Reference Inputs n Pin Description (Cont.) 40-pin DIP 40-pin DIP 44-pin PQFP Pin Number (Reverse) Pin Number 34 (7) 42 35 (6) 43 36 (5) 44 ¢w 1 ¢w 2 37 (4) 3 38 ¢w 39 40 (3) (2) (1) 4 5 6 7 Symbol CREFCREF+ VREF+ DEEN INTEN TEST V+ OSC3 OCS2 OCS1 Description Reference capacitor, negative terminal Reference capacitor, positive terminal Analog-reference input, positive terminal De-integration status flag Integration status flag Display-test pin, When pulled to V+, display should read -1888. Positive supply voltage Buffered OSC1 Crystal oscillator output Crystal oscillator input n Function Description 6 Analog Microelectronics, Inc. AME811/AME811A/AME811R 3-1/2 Digit A/D Converter - Low Power With HOLD And Differential Reference Inputs 1V below the V+. The integrator output can swing within 0.3 V of V+ or V- without increasing linearity errors. Care must be exercised to make sure the integrator output does not saturate. In a typical application, the common mode is eliminated by connecting the INLO to COM, Analog Common. The A/D conversion has the following three phases: 1. Auto-Zero Phase 2. Integration Phase 3. De-integration Phase Auto-Zero Phase The INHI and INLO are shorted to analog common internally. The reference capacitor is charged to the reference voltage. A feedback loop is closed around the system to cancel the offset voltage of buffer, integrator and comparator. Differential Reference (VREF+ & VREF-) The reference voltage can be generated anywhere within the V+ to V-. Under a large common mode voltage, reference capacitor can gain charge during the de-integration of a positive signal. The reference capacitor will lose charge when de-integrating a negative input signal. The difference in reference voltage for positive or negative input voltages can cause the rollover error. To prevent rollover error from being induced by large common-mode voltages, reference capacitor should be large compared to stray node capacitance. Signal Integration phase The converter integrates the differential voltage across the INHI and INLO for a fixed time, 1000 system clocks. The polarity of the signal is determined at the end of this phase. Reference Integration Phase INLO is internally connected to the Analog Common, INHI is connected across the reference capacitor with appropriate polarity determined by the control circuit. The integrator output will then return to zero. The time it takes to return to zero, 1000 x VIN /VREF, is the digital representation of the analog signal. Analog Common (COM) The Analog Common is to set a common mode voltage for the analog signal. The analog common is typically 3.0V below V+, set primary for the battery operated application. Analog common is capable to sink 20 mA. It’s source current is limited to 10 µA. Analog common is therefore easily pulled to a more negative voltage to override the internal reference. When supply voltage is greater than 7V, analog common can be used as reference source with temperature coefficient of typically 50 ppm/OC. Differential Signal Inputs (INHI & INLO) The AME811 has true differential inputs and accepts input signals within the input common mode voltage range (Vcm). Typical range is from 1V above the V- to 7 Analog Microelectronics, Inc. AME811/AME811A/AME811R 3-1/2 Digit A/D Converter - Low Power With HOLD And Differential Reference Inputs n Digital Block Diagrams 8 Analog Microelectronics, Inc. AME811/AME811A/AME811R 3-1/2 Digit A/D Converter - Low Power With HOLD And Differential Reference Inputs Auto-Zero Phase: 1000 to 3000 Counts Signal Integration Phase: 1000 Counts (Fixed) Reference Integration Phase : 0 to 2000 Counts For signals less than full-scale, the unused reference integration time is assigned to the autozero phase. n Digital Section Digital Ground AME811 generates an internal digital ground, typically 5V below the V+. Clock Circuit The clock can be generated in either of the following three methods. 1. An external oscillator connected to “OSC1” 2. A crystal between pins “OSC1” and “OSC2” 3. A R-C oscillator using “OSC1”, “OSC2” and “OSC3” Notes: There is no on-chip feedback resister across osc1 and osc2. Segment Drivers The backplane frequency is 1/800 of the oscillator clock frequency. For example if the oscillator frequency is 48 KHz (3 conversions per second) the backplane frequency will be 60 Hz. The segment and backplane are at the same frequency with a nominal 5 volt amplitude. The segment is visible (ON) when the segment and the backplane are out of phase, otherwise it is invisible (OFF). The polarity segment is “ON” for negative analog inputs. When the TEST pin on the AME811 is pulled to V+, all segments are turned “ON”. The display reads -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. Systems Timing The oscillator frequency is divided by 4 prior to clocking the internal decade counters. Each conversion takes 4000 counts or 16000 oscillator clock pulses. The timing of each phase are as follows: 9 Analog Microelectronics, Inc. AME811/AME811A/AME811R 3-1/2 Digit A/D Converter - Low Power With HOLD And Differential Reference Inputs Integration Status (INTEN) The INTEN is an output signal of the converter, it is “high” during the signal integration phase. This signal can be used as a status indicator or a control to connect the analog signal to the converter for processing. It is available in 44 pin package. Test When the TEST is pulled to V+ all segments and the minus sign will be activated. The TEST pin is tied to the internally generated digital ground through a 500Ω resistor in the AME811. It is typically 5V lower than V+. TEST pin may be used as the negative power supply for external CMOS logic at the maximum current of 1 mA. De-integration Status (DEEN) The DEEN is an output signal of the converter, it is “high” during the reference de-integration phase. The period of the DEEN is proportional to the conversion result. Users may calculate the conversion result by counting the number of clock pulse on the OSC3 pin when DEEN is “high”. The conversion result is equal to (N /4) - 1/2 where N is the number of the pulse at the OSC3 pin. It is available in 44 pin package. Data Hold When the Hold pin is connected to V+ the conversion result will not be updated. The conversion is still free running during the hold mode. n Component Value Selection Auto-Zero Capacitor (Caz) The Caz capacitor size has some influence on system noise. A 0.47µF capacitor is recommended for 200 mV full-scale applications. A 0.047µF capacitor is recommended for 2.0V full-scale applications. A mylar dielectric capacitor is adequate. Reference Capacitor (Cref) A 0.1µF capacitor is acceptable when “INLO” is tied to analog common. If a large common-mode voltage exists and the application requires 200 mV full-scale, increase Cref to 1.0 µF. A mylar dielectric capacitor is adequate. 10 Analog Microelectronics, Inc. AME811/AME811A/AME811R 3-1/2 Digit A/D Converter - Low Power With HOLD And Differential Reference Inputs Oscillator Components R-C Oscillator A 100 KΩ Rosc is recommended for all frequencies. Cosc is selected by using the equation: fosc = 0.45/(RC) For fosc of 48KHz, Cosc is 100pF nominally. To achieve maximum line noise rejection, the signalintegrate period should be a multiple of line period. The optimum oscillator frequencies for 60 Hz and 50 Hz rejection are listed as follows: For 60 Hz rejection: 40KHz, 48KHz, 60KHz etc. For 50 Hz rejection: 40KHz, 50KHz, 66-2/3KHz etc. Integrating Capacitor (Cint) Cint should be selected to maximize the integrator output voltage swing without causing output saturation. A ± 2V full-scale integrator output swing is recommended if “ANALOG COMMON” is used as signal reference. For 3 readings/second (fosc = 48 KHz) a 0.22 µF 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: Cint = [(4000)(1/fosc)(Vfs/Rint)] / Vint where: fosc= Oscillator clock frequency Vfs = Full-scale input voltage Rint = Integrating resistor Vint = Desired full-scale integrator output swing Cint must have low dielectric absorption to minimize rollover error. A polypropylene capacitor is recommended. Reference Voltage Selection A full-scale reading (2000 counts) requires the input signal be twice the reference voltage. F u l l -S c a l e V o l ta g e 200.0 m V 2 .0 0 0 V V re f 100.0 m V 1 .0 0 0 V Integrating Resistor (Rint) The input buffer amplifier and integrator both have a class A output stage with 100 µA quiescent current. The integrator and buffer can supply 20 µA drive currents with negligible linearity errors. Rint is chosen to keep the output stage in the linear region. For a 200mV full-scale, it is 47KΩ; 2.0V full-scale requires 470KΩ. Summary of component selection: F u l l sc a l e Caz R in t C in t V re f 200.0m V 0.47µF 47 K Ω 0.22µF 100.0m V 2.000V 0.047µF 470 K Ω 0.22 µF 1.000V In some applications a scale factor other than unity may exist between a transducer output voltage and the required digital reading. Assume, for example, a pressure transducer output is 600 mV for 2000 Ib/in2. Rather than dividing the input voltage by three the reference voltage should be set to 300 mV. This permits the transducer input to be used directly. The integrator resistor would be 120KΩ. In some temperature and weighting system with variable tare, the offset reading can be generated by connecting the voltage transducer between INHI and COMMON and the variable offset voltage between COMMON and INLO. Low Battery Flag (LB) The low battery flag is set when the supply voltage (V+ to V-) is lower than seven volts, typical. Once the LB is set, the waveform of the LB will be out of phase with the BP (Back Plane) to turn on a low battery annunciator for AME811. Note: fosc = 48 KHz 11 Analog Microelectronics, Inc. AME811/AME811A/AME811R 3-1/2 Digit A/D Converter - Low Power With HOLD And Differential Reference Inputs n Typical Applications 12 Analog Microelectronics, Inc. AME811/AME811A/AME811R 3-1/2 Digit A/D Converter - Low Power With HOLD And Differential Reference Inputs 13 Analog Microelectronics, Inc. AME811/AME811A/AME811R 3-1/2 Digit A/D Converter - Low Power With HOLD And Differential Reference Inputs 14 www.analogmicro.com E-Mail: info@analogmicro.com Life Support Policy: These products of Analog Microelectronics, Inc. are not authorized for use as critical components in lifesupport devices or systems, without the express written approval of the president of Analog Microelectronics, Inc. Analog Microelectronics, Inc. reserves the right to make changes in the circuitry and specifications of its devices and advises its customers to obtain the latest version of relevant information. © Analog Microelectronics, Inc. , July 2001 Document: 1021-duc-B-0704 Corporate Headquarters Analog Microelectronics, Inc. 3100 De La Cruz Blvd. Suite 201 Santa Clara, CA. 95054-2046 Tel : (408) 988-2388 Fax: (408) 988-2489 Asia Pacific Headquarters AME, Inc. 2F, 187 Kang Chien Road, Nei-Hu District Taipei 114, Taiwan, R.O.C. Tel : 886 2 2627-8687 Fax : 886 2 2659-2989