HI7188
8-Channel, 16-Bit, High Precision, Sigma-Delta A/D Sub-System

Key Features

• Fully Differential 8-Channel Multiplexer and Reference
• Automatic Channel Switching with Zero Latency
• 240 Conversions Per Second Per Channel
• 16-Bit Resolution with No Missing Codes
• 0.0015% Integral Non-Linearity
• Fully Software Configurable
• 120dB Rejection of 60/50Hz Line Noise
• Channel Conversion Order and Number of Active Channels
• True Bipolar or Unipolar Input Range Per Channel
• PGIA Gain Per Channel
• 2-Wire or 3-Wire Interface
• Chopper Stabilized PGIA with Gains of 1 to 8
• Serial Data I/O Interface, SPI Compatible
• 3 Point System Calibration
• Low Power Dissipation of 30mW (Typ)

Description

The HI7188 is an easy-to-use 8-Channel sigma-delta programmable A/D subsystem ideal for low frequency physical and electrical measurements in scientific, medical, and industrial applications. The subsystem has complete onchip capabilities to support moving the intelligence from the system controller and towards the sensors. This gives the designer faster and more flexible configurability without the traditional drawbacks of low throughput per channel, higher power or cost per channel. Extreme design complexity and excessive software overhead is eliminated.

The HI7188 contains a fully differential 8 channel multiplexer, Programmable Gain Instrumentation Amplifier (PGIA), 4th order sigma-delta ADC, integrating filter, line noise rejection filters, calibration and data RAMs, clock oscillator, and a microsequencer. Communication with the HI7188 is performed via the serial I/O port, and is compatible with most synchronous transfer formats, including both the Motorola/Intersil 6805/11 series SPI, QSPI and Intel 8051 series SSR protocols.

The powerful on-board microsequencer provides automatic conversions on the multiplexed input channels (up to 8) by controlling all channel switching, filtering and calibration. The microsequencer supports on-the-fly multiplexer reconfiguration, forty to fifty times faster throughput than the competition and zero step response delay during internal or external multiplexer channel changes. A simple set of commands gives the user control over calibration, PGIA gain, and bipolar/unipolar modes on a per channel basis. Number of channels to convert, data coding, line noise rejection, etc. is programmed at the chip level. The calibration RAMs allow the user to read and write system calibration data while the data RAMs provide a read support of the conversion results for each channel.

This design is effectively eight 16-bit (for 96dB noise-free dynamic range) Sigma-Delta A/D converters combined with a microsequencer and an eight-channel multiplexer in a single package. The HI7188 provides 120dB line-noise rejection at 240 samples/second/channel (in 60Hz linerejection mode) and 200 samples/second/channel (in 50Hz line-rejection mode) base output data rates. By reusing multiplexer channels for the same input, throughput can Fully Differential 8-Channel Multiplexer and Reference

Applications

• Multi-Channel Industrial Process Controls
• Weight Scales
• Medical Patient Monitoring
• Laboratory Instrumentation
• Gas Monitoring System
• Reference Literature
• AN9504 "A Brief Introduction to Sigma Delta Conversion"
• TB329 "Intersil Sigma-Delta Calibration Techniques"
• AN9518 "Using the HI7188 Evaluation Kit"
• AN9610 "Interfacing the HI7188 to a Microcontroller"
• AN9538 "Using the HI7188 Serial Interface