FET Input Analog Front End with ADC Driver Data Sheet ADA4350 FEATURES GENERAL DESCRIPTION Low noise, low input bias current FET input amplifier The ADA4350 is an analog front end for photodetectors or other Very low input bias current: 0.25 pA typical at 25C sensors whose output produces a current proportional to the Low input voltage noise sensed parameter or voltage input applications where the system 92 nV/Hz typical at 10 Hz at 5 V requires the user to select between very precise gain levels to 5 nV/Hz typical at 100 kHz at 5 V maximize the dynamic range. Gain bandwidth product: 175 MHz The ADA4350 integrates a FET input amplifier, a switching network, Input capacitance and an ADC driver with all functions controllable via a serial 3 pF typical, differential mode peripheral interface (SPI) or parallel control logic into a single 2 pF typical, common mode IC. The FET input amplifier has very low voltage noise and current Integrated gain switching noise making it an excellent choice to work with a wide range of Sampling and feedback switch off leakage: 0.5 pA typical photodetectors, sensors, or precision data acquisition systems. Worst case t /t times: 105 ns typical/65 ns typical ON OFF Integrated analog-to-digital converter (ADC) driver Its switching network allows the user individual selection of up Differential mode and single-ended mode to six different, externally configurable feedback networks by Adjustable output common-mode voltage using external components for the feedback network, the user 5 V to +3.8 V typical for 5 V supply can more easily match the system to their desired photodetector or Wide output voltage swing: 4.8 V minimum for 5 V supply sensor capacitance. This feature also allows the use of low thermal Linear output current: 18 mA rms typical for 5 V supply drift resistors, if required. SPI or parallel switch control of all functions The design of the switches minimizes error sources so that they Wide operating range: 3.3 V to 12 V add virtually no error in the signal path. The output driver can Quiescent current: 8.5 mA typical (5 V full system) be used in either single-ended or a differential mode and is APPLICATIONS ideal for driving the input of an ADC. Current to voltage (I to V) conversions The ADA4350 can operate from a single +3.3 V supply or a dual Photodiode preamplifiers 5 V supply, offering user flexibility when choosing the polarity of Chemical analyzers the detector. It is available in a Pb-free, 28-lead TSSOP package and Mass spectrometry is specified to operate over the 40C to +85C temperature range. Molecular spectroscopy Multifunction pin names may be referenced by their relevant Laser/LED receivers function only. Data acquisition systems FUNCTIONAL BLOCK DIAGRAM 9 8 7 6 5 4 27 1 28 2 ADA4350 P1 3 VOUT1 S0 S6 IN-N 10 S1 S7 S2 S8 IN-P 11 S9 S3 S4 S10 S5 S11 M1 26 VOUT2 SPI INTERFACE 12 13 16 17 19 20 21 22 23 25 FET AMP SWITCHING NETWORK ADC DRIVER Figure 1. Rev. B Document Feedback 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. No Tel: 781.329.4700 20152016 Analog Devices, Inc. All rights reserved. license is granted by implication or otherwise under any patent or patent rights of Analog Devices. Trademarks and registered trademarks are the property of their respective owners. Technical Support www.analog.com SWA IN SWB IN EN FB0 MODE FB1 LATCH/P0 FB2 SCLK/P1 FB3 SDO/P2 FB4 FB5 SDI/P3 CS/P4 SWA OUT SWB OUT REF VIN1 RF1 12417-001ADA4350 Data Sheet TABLE OF CONTENTS Features .............................................................................................. 1 Typical Performance Characterisitics .......................................... 17 Applications ....................................................................................... 1 Full System .................................................................................. 17 General Description ......................................................................... 1 FET Input Amplifier .................................................................. 19 Functional Block Diagram .............................................................. 1 ADC Driver ................................................................................. 22 Revision History ............................................................................... 2 Test Circuits ..................................................................................... 26 Specifications ..................................................................................... 3 Theory of Operation ...................................................................... 27 5 V Full System ........................................................................... 3 Kelvin Switching Techniques .................................................... 27 5 V FET Input Amplifier ........................................................... 4 Applications Information .............................................................. 28 5 V Internal Switching Network and Digital Pins ................. 5 Configuring the ADA4350 .......................................................... 28 5 V ADC Driver ......................................................................... 6 Selecting the Transimpedance Gain Paths Manually or Through the Parallel Interface .................................................. 28 5 V Full System ............................................................................. 8 Selecting the Transimpedance Gain Paths Through the 5 V FET Input Amplifier ............................................................. 9 SPI Interface (Serial Mode) ....................................................... 28 5 V Internal Switching Network and Digital Pins .................. 10 SPICE Model ............................................................................... 30 5 V ADC Driver .......................................................................... 11 Transimpedance Amplifier Design Theory ................................ 32 Timing Specifications ................................................................ 13 Transimpedance Gain Amplifier Performance ...................... 34 Absolute Maximum Ratings .......................................................... 15 The Effect of Low Feedback Resistor RFx ................................ 35 Thermal Resistance .................................................................... 15 Using The T Network to Implement Large Feedback Maximum Power Dissipation ................................................... 15 Resistor Values ............................................................................ 36 ESD Caution ................................................................................ 15 Outline Dimensions ....................................................................... 37 Pin Configuration and Function Descriptions ........................... 16 Ordering Guide .......................................................................... 37 REVISION HISTORY 3/16Rev. A to Rev. B Change to Table 15 ......................................................................... 29 12/15Rev. 0 to Rev. A Changes to Table 1 ............................................................................ 3 Changes to Table 5 ............................................................................ 8 Deleted Figure 4 Renumbered Sequentially ............................... 14 Changes to Table 10 ........................................................................ 15 Changes to Table 14 ........................................................................ 29 4/15Revision 0: Initial Version Rev. B Page 2 of 37