Datasheet AD7191 (Analog Devices) - 19

AD7191
In systems where the AGND and DGND pins are connected sides of the board should run at right angles to each other. somewhere else in the system(that is, at the system power This reduces the effects of feedthrough through the board. supply), they should not be connected again at the AD7191 A microstrip technique is by far the best but is not always because a ground loop results. In these situations, it is possible with a double-sided board. In this technique, the recommended that the AD7191 AGND and DGND pins be tied component side of the board is dedicated to ground planes, to the AGND plane. In any layout, it is important that the user and signals are placed on the solder side. keep in mind the flow of currents in the system, ensuring that Good decoupling is important when using high resolution the return paths for all currents are as close as possible to the ADCs. All analog supplies should be decoupled with 10 μF paths the currents took to reach their destinations. Avoid tantalum capacitors in parallel with 0.1 μF capacitors to AGND. forcing digital currents to flow through the AGND sections of To achieve the best from these decoupling components, they the layout. have to be placed as close as possible to the device, ideally right Avoid running digital lines under the device because these up against the device. All logic chips should be decoupled with couple noise onto the die. The analog ground plane should be 0.1 μF ceramic capacitors to DGND. In systems where a allowed to run under the AD7191 to prevent noise coupling. common supply voltage is used to drive both the AVDD and The power supply lines to the AD7191 should use as wide a DVDD of the AD7191, it is recommended that the system AVDD trace as possible to provide low impedance paths and reduce supply be used. This supply should have the recommended the effects of glitches on the power supply line. Fast switching analog supply decoupling capacitors between the AVDD pin of signals like clocks should be shielded with digital ground to the AD7191 and AGND, and the recommended digital supply avoid radiating noise to other sections of the board, and clock decoupling capacitor between the DVDD pin of the AD7191 and signals should never be run near the analog inputs. Avoid DGND. crossover of digital and analog signals. Traces on opposite Rev. A | Page 18 of 20 Document Outline FEATURES INTERFACE APPLICATIONS GENERAL DESCRIPTION FUNCTIONAL BLOCK DIAGRAM TABLE OF CONTENTS REVISION HISTORY SPECIFICATIONS TIMING CHARACTERISTICS TIMING DIAGRAM ABSOLUTE MAXIMUM RATINGS ESD CAUTION PIN CONFIGURATION AND FUNCTION DESCRIPTIONS TYPICAL PERFORMANCE CHARACTERISTICS RMS NOISE AND RESOLUTION SPECIFICATIONS ADC CIRCUIT INFORMATION OVERVIEW FILTER, DATA RATE, AND SETTLING TIME GAIN ANALOG INPUT CHANNELS TEMPERATURE SENSOR POWER-DOWN (PDOWN) CLOCK BIPOLAR CONFIGURATION DATA OUTPUT CODING BRIDGE POWER-DOWN SWITCH REFERENCE DIGITAL INTERFACE GROUNDING AND LAYOUT APPLICATIONS INFORMATION WEIGH SCALES EMI RECOMMENDATIONS OUTLINE DIMENSIONS ORDERING GUIDE