ADS1118_13 Datasheet, PDF (14/38 Pages) Texas Instruments – Ultra-Small, Low-Power, SPI™-Compatible, 16-Bit Analog-to-Digital Converter and Temperature Sensor with Internal Reference

ADS1118
SBAS457C – OCTOBER 2010 – REVISED FEBRUARY 2013
www.ti.com
MULTIPLEXER
The ADS1118 contains an input multiplexer, as shown in Figure 39. Either four single-ended or two differential
signals can be measured. Additionally, AIN0, AIN1, and AIN2 may be measured differentially to AIN3. The
multiplexer is configured by three bits (MUX[2:0], bits 14-12) in the Config register. When single-ended signals
are measured, the negative input of the ADC is internally connected to GND by a switch within the multiplexer.
VDD
Device
AIN0
AIN1
AIN2
AIN3
VDD
GND
VDD
GND
VDD
GND
AIN_P
AIN_N
GND
GND
Figure 39. ADS1118 MUX
When measuring single-ended inputs, note that the negative range of the output codes is not used. These codes
are intended for measuring negative differential signals, such as (AIN_P – AIN_N) < 0. Electrostatic discharge (ESD)
diodes to VDD and GND protect the ADS1118 inputs. To prevent the ESD diodes from turning on, the absolute
voltage on any input must stay within the range given in Equation 1:
GND – 0.3 V < AINx < VDD + 0.3 V
(1)
If the voltages on the input pins can possibly violate these conditions, external Schottky clamp diodes and series
resistors may be required to limit the input current to safe values (see the Absolute Maximum Ratings table).
Although the analog inputs can support signals marginally above supply, under no circumstances should any
analog or digital input or output be driven to greater than 5.5 V with respect to the GND pin.
Also, overdriving one unused input on the ADS1118 may affect conversions currently taking place on other input
pins. If overdriving unused inputs is possible, TI recommends clamping the signal with external Schottky diodes.
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