Datasheet

ADC10731, ADC10732, ADC10734, ADC10738
www.ti.com SNAS081D –MAY 1999–REVISED MARCH 2013
Figure 39. Detailed Diagram of the ADC10738 DAC and Analog Multiplexer Stages
APPLICATIONS INFORMATION
Multiplexer Configuration
The design of these converters utilizes a sampled-data comparator structure, which allows a differential analog
input to be converted by the successive approximation routine.
The actual voltage converted is always the difference between an assigned “+” input terminal and a “−” input
terminal. The polarity of each input terminal or pair of input terminals being converted indicates which line the
converter expects to be the most positive.
A unique input multiplexing scheme has been utilized to provide multiple analog channels. The input channels
can be software configured into three modes: differential, single-ended, or pseudo-differential. Analog Input
Multiplexer Options illustrates the three modes using the 4-channel MUX of the ADC10734. The eight inputs of
the ADC10738 can also be configured in any of the three modes. The single-ended mode has CH0–CH3
assigned as the positive input with COM serving as the negative input. In the differential mode, the ADC10734
channel inputs are grouped in pairs, CH0 with CH1 and CH2 with CH3. The polarity assignment of each channel
in the pair is interchangeable. Finally, in the pseudo-differential mode CH0–CH3 are positive inputs referred to
COM which is now a pseudo-ground. This pseudo-ground input can be set to any potential within the input
common-mode range of the converter. The analog signal conditioning required in transducer-based data
acquisition systems is significantly simplified with this type of input flexibility. One converter package can now
handle ground-referred inputs and true differential inputs as well as signals referred to a specific voltage.
The analog input voltages for each channel can range from 50 mV below GND to 50 mV above V
+
= DV
+
= AV
+
without degrading conversion accuracy. If the voltage on an unselected channel exceeds these limits it may
corrupt the reading of the selected channel.
Reference Considerations
The voltage difference between the V
REF
+
and V
REF
−
inputs defines the analog input voltage span (the difference
between V
IN
(Max) and V
IN
(Min)) over which 1023 positive and 1024 negative possible output codes apply.
The value of the voltage on the V
REF
+
or V
REF
−
inputs can be anywhere between AV
+
+ 50 mV and −50 mV, so
long as V
REF
+
is greater than V
REF
−
. The ADC10731/2/4/8 can be used in either ratiometric applications or in
systems requiring absolute accuracy. The reference pins must be connected to a voltage source capable of
driving the minimum reference input resistance of 5 kΩ.
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Product Folder Links: ADC10731 ADC10732 ADC10734 ADC10738