ADS1118_13 Datasheet, PDF (25/38 Pages) Texas Instruments – Ultra-Small, Low-Power, SPI™-Compatible, 16-Bit Analog-to-Digital Converter and Temperature Sensor with Internal Reference

ADS1118
www.ti.com
SBAS457C – OCTOBER 2010 – REVISED FEBRUARY 2013
APPLICATION INFORMATION
The following sections give example circuits and suggestions for using the ADS1118 in various situations.
BASIC CONNECTIONS AND LAYOUT CONSIDERATIONS
For many applications, connecting the ADS1118 is simple. A basic connection diagram for the ADS1118 is
shown in Figure 47. Most microcontroller SPI peripherals can operate with the ADS1118. The interface operates
in SPI mode 1 where CPOL = 0 and CPHA = 1. In SPI mode 1, SCLK idles low and data are launched or
changed only on SCLK rising edges; data are latched or read by the master and slave on SCLK falling edges.
Details of the SPI communication protocol employed by the ADS1118 can be found in the SPI Timing
Characteristics section. Although not required, placing 49.9-Ω resistors in series with all of the digital pins is good
practice. This resistance smooths sharp transitions, suppresses overshoot, and offers some overvoltage
protection. Care must be taken to still meet all SPI timing requirements because the additional resistors interact
with the bus capacitances present on the digital signal lines.
Microcontroller or
Microprocessor
with SPI Port
DOUT
DIN
CS
SCLK
Device
10
DIN
1 SCLK DOUT/DRDY 9
2 CS
VDD 8
3 GND
AIN3 7
4 AIN0
AIN1
5
AIN2 6
VDD
0.1mF (typ)
Inputs Selected
from Configuration
Register
Figure 47. Typical Connections of the ADS1118
The fully-differential input of the ADS1118 is ideal for connecting to differential sources (such as thermocouples
and thermistors) with a moderately low source impedance. Although the ADS1118 can read bipolar differential
signals, the device cannot accept negative voltages on either input because every pin on the ADS1118 employs
the use of ESD protection diodes. In the event that an input exceeds supply or drops below ground, these diodes
begin to turn on. Therefore, thinking of the ADS1118 positive input as noninverting, and of the negative input as
inverting may be helpful.
The 0.1-μF bypass capacitor supplies the momentary bursts of extra current required from the supply when the
ADS1118 is converting. This bypass capacitor should be placed as close to the device as possible. For very
sensitive systems, or systems in harsh noise environments, avoiding the use of vias for connecting the bypass
capacitor may offer superior bypass and noise immunity.
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