3 nV/Hz, Low Power Instrumentation Amplifier Data Sheet AD8421 FEATURES TYPICAL APPLICATION DIAGRAM +5V 10 Low power +12V ADR435 10k 1F 0.1F 2.3 mA maximum supply current 2.5V 10k Low noise +12V +IN 3.2 nV/Hz maximum input voltage noise at 1 kHz G = 10 SPI 200 fA/Hz current noise at 1 kHz REF VDD VIO INTERFACE 100 1.1k IN+ AD8421 SDI Excellent ac specifications 3nF REF SCK 10 MHz bandwidth (G = 1) AD7685 IN SDO 2 MHz bandwidth (G = 100) 12V IN CNV 0.6 s settling time to 0.001% (G = 10) GND 80 dB CMRR at 20 kHz (G = 1) 2.5V + OP1177 35 V/s slew rate 10F High precision dc performance (AD8421BRZ) 94 dB CMRR minimum (G = 1) 5k 0.2 V/C maximum input offset voltage drift Figure 1. AD8421 Driving 16-Bit AD7685 1 ppm/C maximum gain drift (G = 1) 10 G = 100 500 pA maximum input bias current Inputs protected to 40 V from opposite supply BEST AVAILABLE 7mA LOW NOISE IN-AMP 1 2.5 V to 18 V dual supply (5 V to 36 V single supply) Gain set with a single resistor (G = 1 to 10,000) Available in 8-lead LFCSP, 8-lead MSOP, and 8-lead SOIC 100n APPLICATIONS BEST AVAILABLE 1mA LOW POWER IN-AMP Medical instrumentation 10n Precision data acquisition AD8421 Microphone preamplification R NOISE ONLY S Vibration analysis 1n 100 1k 10k 100k 1M Multiplexed input applications SOURCE RESISTANCE, R () S ADC driver Figure 2. Noise Density vs. Source Resistance GENERAL DESCRIPTION The AD8421 is a low cost, low power, extremely low noise, The AD8421 delivers 3 nV/Hz input voltage noise and ultralow bias current, high speed instrumentation amplifier that 200 fA/Hz current noise with only 2 mA quiescent current, is ideally suited for a broad spectrum of signal conditioning and making it an ideal choice for measuring low level signals. For data acquisition applications. This product features extremely applications with high source impedance, the AD8421 employs high CMRR, allowing it to extract low level signals in the presence innovative process technology and design techniques to provide of high frequency common-mode noise over a wide noise performance that is limited only by the sensor. temperature range. The AD8421 uses unique protection methods to ensure robust The 10 MHz bandwidth, 35 V/s slew rate, and 0.6 s settling inputs while still maintaining very low noise. This protection time to 0.001% (G = 10) allow the AD8421 to amplify high speed allows input voltages up to 40 V from the opposite supply rail signals and excel in applications that require high channel count, without damage to the part. multiplexed systems. Even at higher gains, the current feedback A single resistor sets the gain from 1 to 10,000. The reference architecture maintains high performance for example, at G = 100, pin can be used to apply a precise offset to the output voltage. the bandwidth is 2 MHz and the settling time is 0.8 s. The The AD8421 is specified from 40C to +85C for the 8-lead AD8421 has excellent distortion performance, making it suitable MSOP and SOIC packages, and from 40C to +125C for the for use in demanding applications such as vibration analysis. 8-lead LFCSP package. Rev. A Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. rights of third parties that may result from its use. Specifications subject to change without notice. Tel: 781.329.4700 www.analog.com No license is granted by implication or otherwise under any patent or patent rights of Analog Fax: 781.461.3113 20122020 Analog Devices, Inc. All rights reserved. Devices. Trademarks and registered trademarks are the property of their respective owners. TOTAL NOISE DENSITY AT 1kHz (V/Hz) 10123-078 10123-101AD8421 Data Sheet TABLE OF CONTENTS Features .............................................................................................. 1 Architecture ................................................................................ 22 Applications ...................................................................................... 1 Gain Selection ............................................................................. 22 Typical Application Diagram ......................................................... 1 Reference Terminal .................................................................... 23 General Description ......................................................................... 1 Input Voltage Range .................................................................. 23 Revision History ............................................................................... 2 Layout .......................................................................................... 23 Specifications .................................................................................... 3 Input Bias Current Return Path ............................................... 24 AR and BR Grades ....................................................................... 3 Input Voltages Beyond the Supply Rails ................................. 24 ARM and BRM Grades ................................................................ 5 Radio Frequency Interference (RFI) ....................................... 25 ACP Grade .................................................................................... 7 Calculating the Noise of the Input Stage ................................ 25 Absolute Maximum Ratings ......................................................... 10 Applications Information ............................................................. 27 Thermal Resistance .................................................................... 10 Differential Output Configuration .......................................... 27 ESD Caution................................................................................ 10 Driving an ADC ......................................................................... 28 Pin Configurations and Function Descriptions ......................... 11 Outline Dimensions ....................................................................... 29 Typical Performance Characteristics ........................................... 12 Ordering Guide .......................................................................... 30 Theory of Operation ...................................................................... 22 REVISION HISTORY 10/2020Rev. 0 to Rev. A Changes to Table 5 ......................................................................... 10 Added 8-Lead LFCSP .................................................... Throughout Changes to Figure 44 ..................................................................... 18 Changed Pin Connection Diagram Section to Typical Changes to Figure 72 ..................................................................... 28 Application Diagram Section ......................................................... 1 Added Figure 76 Renumbered Sequentially .............................. 29 Changes to Features Section, Figure 1, and General Changes to Ordering Guide .......................................................... 30 Description Section .......................................................................... 1 Added ACP Grade Section and Table 3 Renumbered 5/2012Revision 0: Initial Version Sequentially ....................................................................................... 7 Rev. A Page 2 of 31