ALD500

Features:

• Resolution up to 18 bits plus sign bit and over-range bit
• Accuracy independent of input source impedances
• High input impedance of 1012 Ω
• Inherently filters and integrates any external noise spikes
• Differential analog input
• Wide bipolar analog input voltage range ±3.5V
• Automatic zero offset compensation
• Low linearity error - as low as 0.002%
• Fast zero-crossing comparator - 1µs
• Low power dissipation - 6mW typical
• Automatic internal polarity detection
• Low input current - 2pA typical
• Microprocessor controlled conversion
• Optional digital control from a microcontroller, an ASIC, or a dedicated digital circuit
• Flexible conversion speed versus resolution trade-off


Application

• 4 1/2 digits to 5 1/2 digits plus sign measurements
• Precision analog signal processor
• Precision sensor interface
• High accuracy DC measurement functions
• Portable battery operated instruments
• Computer peripheral
• PCMCIA


Specifications

Supply voltage, V+                                                                      13.2V
Differential input voltage range                                -0.3V to V+ +0.3V
Power dissipation                                                                    600 mW
Operating temperature range PC, SC, SWC package   0°C to +70°C
Storage temperature range                                    -65°C to +150°C
Lead temperature, 10 seconds                                               +260°C


Description

The ALD500AU/ALD500A/ALD500 are integrating dual slope analog processors, designed to operate on ±5V power supplies for building precision analog-to-digital converters. The ALD500AU/ALD500A/ ALD500 feature specifications suitable for 18 bit/17 bit/16 bit  resolution conversion, respectively.  Together with three capacitors, one resistor, a precision voltage reference, and a digital controller, a precision Analog to Digital converter with auto zero can be implemented. The digital controller can be implemented by an external microcontroller, under either hardware (fixed logic) or software control. For ultra high resolution applications, up to 23 bit conversion can be implemented with
an appropriate digital controller and software.

The ALD500AU/ALD500A/ALD500  analog processors accept differential inputs and the external digital controller first counts the number of pulses at a fixed clock rate that a capacitor requires to integrate against an unknown analog input voltage, then counts the number of pulses required to deintegrate the capacitor against a known reference voltage.  This
unknown analog voltage can then be converted by the microcontroller to a digital word, which is translated into a high resolution number, representing an accurate reading.  This reading, when ratioed against the reference voltage, yields an accurate, absolute voltage measurement reading.

The ALD500AU/ALD500A/ALD500  analog processors consist of on-chip digital control circuitry to accept control inputs, integrating buffer amplifiers, analog switches, and voltage comparators.  It functions in four operating modes, or phases, namely auto zero, integrate, deintegrate, and integrator zero phases.  At the end of a conversion, the comparator output goes from high to low when the integrator crosses zero during deintegration.

ALD500AU/ALD500A/ALD500 analog processors also provide direct logic interface to CMOS logic families.