ADS1255IDB Burr-Brown Corporation, ADS1255IDB Datasheet - Page 14

• Manufacturer Part Number: ADS1255IDB
• Description: Very Low Noise/ 24-Bit Analog-to-Digital Converter
• Manufacturer: Burr-Brown Corporation

ADS1255
ADS1256
SBAS288D − JUNE 2003 − REVISED AUGUST 2004
INPUT MULTIPLEXER
Figure 6 shows a simplified diagram of the input
multiplexer. This flexible block allows any analog input pin
to be connected to either of the converter differential
inputs. That is, any pin can be selected as the positive
input (AIN
negative input (AIN
the multiplexer register.
The ADS1256 offers nine analog inputs, which can be
configured as four independent differential inputs, eight
single-ended inputs, or a combination of differential and
single-ended inputs.
The ADS1255 offers three analog inputs, which can be
configured as one differential input or two single-ended
inputs. When using the ADS1255 and programming the
input, make sure to select only the available inputs when
programming the input multiplexer register.
In general, there are no restrictions on input pin selection.
14
P
); likewise, any pin can be selected as the
N
). The pin selection is controlled by
AINCOM
AIN0
AIN1
AIN2
AIN3
AIN4
AIN5
AIN6
AIN7
Figure 6. Simplified Diagram of the Input Multiplexer
ADS1256 Only
AVDD AGND
AVDD
AVDD
AVDD
AVDD
AVDD
AVDD
AVDD
AVDD
Input Multiplexer
However, for optimum analog performance, the following
recommendations are made:
1. For differential measurements use AIN0 through
2. For single-ended measurements use AINCOM as
3. Leave any unused analog inputs floating. This
ESD diodes protect the analog inputs. To keep these
diodes from turning on, make sure the voltages on the
input pins do not go below AGND by more than 100mV,
and likewise do not exceed AVDD by more than 100mV:
−100mV < (AIN0 − 7 and AINCOM) < AVDD + 100mV.
When using ADS1255/6 for single-ended measurements,
it is important to note that common input AINCOM does not
need to be tied to ground. For example, AINCOM can be
tied to a midpoint reference such as +2.5V or even AVDD.
AIN7, preferably adjacent inputs. For example, use
AIN0 and AIN1. Do not use AINCOM.
common input and AIN0 through AIN7 as
single-ended inputs.
minimizes the input leakage current.
AGND
AVDD
AIN
AIN
P
N
Sensor Detect
Current
Source
Sensor Detect
Current
Source
Buffer
Input
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