ADVANCED LINEAR ALD500RAU/ALD500RA/ALD500R DEVICES, INC. PRECISION INTEGRATING ANALOG PROCESSOR WITH PRECISION VOLTAGE REFERENCE BENEFITS APPLICATIONS 4 1/2 digits to 5 1/2 digits plus sign measurements Low cost, simple functionality Precision analog signal processor Wide dynamic signal range Precision sensor interface Very high noise immunity High accuracy DC measurement functions Automatic compensation and cancellation Portable battery operated instruments of error sources Computer peripheral Easy to use to acquire bipolar signals PCMCIA Up to 19 bit (18 bit + sign bit) single conversion or 21 bit (20 bit + sign bit) multiple conversion and noise performance Inherently linear and stable with temperature and component variations FEATURES Resolution up to 18 bits plus sign bit and over-range bit Accuracy independent of input source impedances PIN CONFIGURATION Accurate on-chip voltage reference Tempco as low as 10 ppm/C guaranteed ALD500R Chip select - power down mode 12 High input impedance of 10 IB 1 20 C S Inherently filters and integrates any external noise spikes + C 2 19 V INT Differential analog input - V 3 18 DGND Wide bipolar analog input voltage range 3.5V C 4 17 C AZ OUT Automatic zero offset compensation B 5 16 B UF Low linearity error - as low as 0.001% typical AGND 6 15 A Fast zero-crossing comparator - 1s - + C 7 14 V REF IN Low power dissipation - 6mW typical + 8 - C 13 V Automatic internal polarity detection REF IN 9 12 + Low input current - 2pA typical N/C V REF 10 11 - Optional digital control from a microcontroller, an ASIC, or N/C V REF a dedicated digital circuit QE, PE, SE PACKAGE Flexible conversion speed vs. resolution trade-off - * N/C pin is connected internally. Connect to V . Ordering Information Resolution Endpoint Voltage Reference Package Type Operating Linearity Accuracy/Tempco Temperature 20L PDIP 20L SOIC 20L QSOP 20LCDIP 16 bit 0.015% 0.5% 50ppm/C ALD500R-50PE ALD500R-50SE ALD500R-50QE 0C to 70C 17 bit 0.01% 0.3% 20ppm/C ALD500RA-20PE ALD500RA-20SE ALD500RA-20QE 0C to 70C 18 bit 0.005% ALD500RAU-20PE ALD500RAU-20SE ALD500RAU-20QE 17 bit 0.01% 0.2% 10ppm/C ALD500RA-10PE ALD500RA-10SE ALD500RA-10QE 0C to 70C 18 bit 0.005% ALD500RAU-10PE ALD500RAU-10SE ALD500RAU-10QE 17 bit 0.01% 0.3% 20ppm/C ALD500RA-20PEI ALD500RA-20SEI ALD500RA-20QEI -40C to +85C 18 bit 0.005% ALD500RAU-20PEI ALD500RAU-20SEI ALD500RAU-20QEI 18 bit 0.005% 0.3% 20ppm/C ALD500RAU-20DE -55C to +125C * Contact factory for customized voltage reference voltage levels, accuracy and tempco specifications. Rev. 1.01 1999 Advanced Linear Devices, Inc., 415 Tasman Drive, Sunnyvale, California 94089-1706 Tel: (408) 747-1155, Fax: (408) 747-1286 FIGURE 1. ALD500R Functional Block Diagram C R C REF INT INT - + V V REF REF (11) C (12) AZ R + REF - C C C INT R = 100K BUF C REF REF REF AZ (2) C = 0.1F (5) B (8) (7) (4) REF INT SW SW R R - SW IN Buffer Integrator + + V IN - (14) + - + SW SW R R + - Comp1 - Level Comp2 C OUT Shift + (17) SW Az SW AZ + - SW SW SW R R S Polarity DGND Detection AGND (18) (6) SW SW IN G - V Analog IN Phase (13) Switch Decoding Control REF Logic Bias Signals Control A B V V N/C N/C SS DD C C B S (15) (16) (3) (19) (10) (9) I B (20) Control Logic (1) GENERAL THEORY OF OPERATION GENERAL DESCRIPTION The ALD500RAU/ALD500RA/ALD500R are integrating Dual-Slope Conversion Principles of Operation dual slope analog processors, designed to operate on 5V power supplies for building precision analog-to-digital The basic principle of dual-slope integrating analog to digital converters. The ALD500RAU/ALD500RA/ALD500R converter is simple and straightforward. A capacitor, C , is INT feature specifications suitable for 18 bit/17 bit/16 bit charged with the integrator from a starting voltage, V , for a X resolution conversion, respectively. Together with three fixed period of time at a rate determined by the value of an capacitors, two resistors, and a digital controller, a precision unknown input voltage, which is the subject of measurement. Analog to Digital converter with auto zero can be Then the capacitor is discharged at a fixed rate, based on an implemented. The digital controller can be implemented where the discharge external reference voltage, back to V X by an external microcontroller, under either hardware time, or deintegration time, is measured precisely. Both the (fixed logic) or software control. For ultra high resolution integration time and deintegration time are measured by a applications, up to 23 bit conversion can be implemented digital counter controlled by a crystal oscillator. It can be with an appropriate digital controller and software. demonstrated that the unknown input voltage is determined by the ratio of the deintegration time and integration time, and The ALD500R series of analog processors accept is directly proportional to the magnitude of the external reference differential inputs and the external digital controller first voltage. counts the number of pulses at a fixed clock rate that a capacitor requires to integrate against an unknown analog The major advantages of a dual-slope converter are: input voltage, then counts the number of pulses required a. Accuracy is not dependent on absolute values of to deintegrate the capacitor against a known internal integration time t and deintegration time t , but is INT DINT reference voltage. This unknown analog voltage can then dependent on their relative ratios. Long-term clock frequency be converted by the microcontroller to a digital word, which variations will not affect the accuracy. A standard crystal is translated into a high resolution number, representing controlled clock running digital counters is adequate to generate an accurate reading. This reading, when ratioed against very high accuracies. the reference voltage, yields an accurate, absolute voltage measurement reading. b. Accuracy is not dependent on the absolute values of R C , as long as the component values do not vary INT and INT The ALD500R analog processors consist of on-chip digital through a conversion cycle, which typically lasts less than 1 control circuitry to accept control inputs, integrating buffer second. amplifiers, analog switches, and voltage comparators and a highly accurate, ultra-stable voltage reference. It c. Offset voltage values of the analog components, such functions in four operating modes, or phases, namely auto as V , are cancelled out and do not affect accuracy. X zero, integrate, deintegrate, and integrator zero phases. At the end of a conversion, the comparator output goes d. Accuracy of the system depends mainly on the accuracy from high to low when the integrator crosses zero during and the stability of the voltage reference value. deintegration. ALD500R analog processors also provide direct logic interface to CMOS logic families. 2 Advanced Linear Devices ALD500RAU/ALD500RA/ALD500R