Datasheet

0.1 F(typ)m

VDD

SCLK

GND

AIN0

AIN1

DIN

DOUT/DRDY

VDD

AIN3

AIN2

Device

InputsSelected

fromConfiguration

ADS1118

SBAS457D –OCTOBER 2010–REVISED OCTOBER 2013

www.ti.com

USING GPIO PORTS FOR COMMUNICATION

Most microcontrollers have programmable input/output (I/O) pins that can be set in software to act as inputs or

outputs. If an SPI controller is not available, the ADS1118 can be connected to GPIO pins and the SPI bus

protocol can be simulated. Using GPIO pins to generate the SPI interface only requires that the pins be

configured as push or pull inputs or outputs. Furthermore, if the SCLK line is held low for more than 28 ms, the

communication times out. This condition means that the GPIO ports must be capable of providing SCLK pulses

with no more than 28 ms between pulses.

SINGLE-ENDED INPUTS

Although the ADS1118 has two differential inputs, the device can easily measure four single-ended signals.

Figure 50 shows a single-ended connection scheme. The ADS1118 is configured for single-ended measurement

by configuring the MUX to measure each channel with respect to ground. Data are then read out of one input

based on the selection in the Config register. The single-ended signal can range from 0 V up to positive supply

or +FS, whichever is lower. Negative voltages cannot be applied to this circuit because the ADS1118 can only

accept positive voltages with respect to ground. The ADS1118 does not loose linearity within the input range.

The ADS1118 offers a differential input voltage range of ±FS. The single-ended circuit shown in Figure 50

however only uses the positive half of the ADS1118 FS input voltage range because it does not produce

differentially negative inputs. Because only half of the FS range is used, one bit of resolution is lost. For optimal

noise performance, TI recommends using differential configurations whenever possible. Differential

configurations maximize the dynamic range of the ADC and provide strong attenuation of common-mode noise.

NOTE: Digital pin connections omitted for clarity.

Figure 50. Measuring Single-Ended Inputs

The ADS1118 is also designed to allow AIN3 to serve as a common point for measurements by adjusting the

MUX configuration. AIN0, AIN1, and AIN2 can all be measured with respect to AIN3. In this configuration the

ADS1118 can operate with inputs where AIN3 serves as the common point. This ability improves the usable

range over the single-ended configuration because it allows negative differential voltages when GND < AIN3 <

VDD; however, it does not offer attenuation of common-mode noise.

Product Folder Links: ADS1118