160 dB Range, 100 pA to 10 mA Logarithmic Converter Data Sheet ADL5303 FEATURES SIMPLIFIED BLOCK DIAGRAM VPS2 PWDN VPS1 Optimized for fiber optic photodiode interfacing 10 16 12 8 full decades of range ADL5303 Law conformance: 0.1 dB from 1 nA to 1 mA VREF PDB BIAS VREF 6 Single-supply operation: 3.0 V to 5.5 V VPDB 5 ~10k 0.5V Complete and temperature stable VSUM Accurate laser trimmed scaling 2 VLOG 8 I PD INPT Logarithmic slope of 10 mV/dB (at the VLOG pin) TEMPERATURE 3 BFIN COMPENSATION 9 5k Basic logarithmic intercept at 100 pA VSUM 4 BFNG Easy adjustment of slope and intercept 13 Output bandwidth of 10 MHz, 15 V/s slew rate Miniature 16-lead package (LFCSP) Low power: ~4.5 mA quiescent current (enabled) 15 7 14 11 GND ACOM GND VOUT APPLICATIONS Figure 1. High accuracy optical power measurement Wide range baseband log compression Versatile detector for APC loops GENERAL DESCRIPTION The ADL5303 is a monolithic logarithmic detector optimized input pin INPT is flanked by the VSUM guard pins that track for the measurement of low frequency signal power in fiber the voltage at the summing node. Connecting the exposed pad optic systems and offers a large dynamic range in a versatile of the device to the VSUM pins provides a continuous guard to and easily used form. Wide measurement range and accuracy minimize leakage into the INPT pin. are achieved using proprietary design and precise laser trimming. The default value of the logarithmic slope at the VLOG output The ADL5303 requires only a single positive supply, V , of 5 V. PS is set by an internal 5 k resistor. Logarithmic slope can be When using low supply voltages, the log slope can be altered to lowered with an external shunt resistor or increased using the fit the available span. Low quiescent current and chip disable buffer and a pair of external feedback resistors. The addition of facilitate use in battery-operated applications. a capacitor at the VLOG pin provides a simple low-pass filter. The input current, IPD, flows in the collector of an optimally The intermediate voltage, VLOG, is buffered in an output stage scaled NPN transistor, connected in a feedback path around a that can swing to within about 100 mV of ground and the posi- low offset JFET amplifier. The current summing input node tive supply, V , and provides a peak current drive capacity of PS operates at a constant voltage, independent of current, with a 20 mA. An on-board 2 V reference is provided to facilitate the default value of 0.5 V this may be adjusted over a wide range. repositioning of the intercept. The incremental bandwidth of a An adaptive biasing scheme is provided for reducing photo- translinear logarithmic amplifier inherently diminishes for diode dark current at very low light input levels. The VPDB pin small input currents. At IPD =1 nA, the bandwidth of the applies approximately 0.1 V reverse bias across the photodiode ADL5303 is approximately 2 kHz increasing in proportion to for IPD = 100 pA, rising linearly to 2.0 V of reverse bias at IPD = IPD up to a maximum value of 10 MHz. 10 mA to improve response time at higher power levels. The Rev. D 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. Tel: 781.329.4700 20132020 Analog Devices, Inc. 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Trademarks and registered trademarks are the property of their respective owners. 10661-001ADL5303 Data Sheet TABLE OF CONTENTS Features .............................................................................................. 1 Bandwidth and Noise Considerations .................................... 10 Applications ...................................................................................... 1 Chip Enable ................................................................................. 11 Simplified Block Diagram ............................................................... 1 Using the ADL5303 ........................................................................ 12 General Description ......................................................................... 1 Slope and Intercept Adjustments............................................. 12 Revision History ............................................................................... 2 Low Supply Slope and Intercept Adjustment ............................ 15 Specifications .................................................................................... 3 Changing the Voltage at the Summing Node ........................... 15 Absolute Maximum Ratings ........................................................... 4 Using the Adaptive Bias ............................................................ 16 ESD Caution.................................................................................. 4 Applications Information ............................................................. 17 Pin Configuration and Function Descriptions ............................ 5 Rescaling ...................................................................................... 17 Typical Performance Characteristics ............................................. 6 Inverting the Slope ..................................................................... 17 Theory of Operation ...................................................................... 10 Evaluation Board ........................................................................ 18 Basic Concepts ............................................................................ 10 Shields and Guards .................................................................... 18 Optical Measurements ............................................................... 10 Outline Dimensions ....................................................................... 21 Decibel Scaling ............................................................................ 10 Ordering Guide .......................................................................... 21 REVISION HISTORY 10/2020Rev. C to Rev. D 6/2018Rev. A to Rev. B Changes to Data Sheet Title ............................................................ 1 Changes to Figure 2 .......................................................................... 5 Changes to Slope and Intercept Adjustments Section and Updated Outline Dimensions ...................................................... 21 Table 4 .............................................................................................. 12 Changes to Ordering Guide .......................................................... 21 Changes to Figure 28 ..................................................................... 15 1/2014Rev. 0 to Rev. A Changes to Evaluation Board Section ......................................... 18 Changes to Slope and Intercept Adjustments Section .............. 14 Changes to Figure 31 ..................................................................... 19 Changes to Table 7 ......................................................................... 20 1/2013Revision 0: Initial Version 10/2019Rev. B to Rev. C Change to Table 3 ............................................................................. 5 Changes to Figure 31 ..................................................................... 19 Changes to Table 7 ......................................................................... 20 Rev. D Page 2 of 21