AN-10840 pages

AN-1084
APPLICATION NOTE
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Channel Switching: AD7190, AD7192, AD7193, AD7194, AD7195
by Mary McCarthy

INTRODUCTION
Σ-Δ ADCs are generally specified in terms of output data rate.
The output data rate is the rate at which conversions are
performed when a single channel is selected and the ADC is
continuously converting. In a multichannel application such as
a data acquisition system, conversions from several channels are
read; that is, each channel is selected in turn and a conversion is
performed for that channel. In such an application, the rate at
which conversions are performed can be different from a single
channel system. This application note describes the switching
procedure used by the AD7190, AD7192, AD7193, AD7194,
and AD7195 parts (hereafter referred to as AD719x).

MULTICHANNEL SYSTEM
In applications such as PLC systems, several input channels are
required to process the multitude of signals or outputs from
sensors. With its PGA and wide range of programmable output
data rates, the AD719x can be used to convert signals of different amplitudes and at different output data rates.

The application generally requires a certain throughput, that is,
a given number of channels need to be read within a given
period of time. The throughput achieved is dependent on the
number of channels to be read and the time taken by the ADC
to convert each channel. The ADCs referred to in this application note have several modes of operation:
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Sinc4 filter or Sinc3 filter
Chop enabled/disabled
Zero latency
Single conversion mode
Automatic channel sequencing

The output data rates allowed and/or the settling time (the time
taken to generate the first conversion after a channel change) is
different for each mode of operation. Therefore, the throughput
also depends on the operating mode.

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