Analog Devices Inc. AD8305ACP-R2

Overview

AD8305ACP-R2 from Analog Devices is a monolithic logarithmic converter IC optimized for photodiode current-to-voltage conversion in fiber optic power monitoring systems. It delivers 100 dB dynamic range (10 nA to 1 mA), ±0.4 dB law conformance error, 200 mV/decade nominal slope, and operates from 3 V to 12 V single supply. Its primary circuit role is precision optical current measurement with temperature-stable log-ratio output at Pin VLOG.

For engineers reviewing the AD8305ACP-R2 datasheet, AD8305ACP-R2 pinout, AD8305ACP-R2 application, or AD8305ACP-R2 equivalent, this page provides verified functional identity, validated 16-pin LFCSP package mapping, confirmed translinear architecture, real-world intercept/slope adjustability, and two rigorously cross-checked alternative logarithmic converters for optical sensing designs.

Technical Context

The AD8305ACP-R2 implements a matched BJT translinear core with dual logarithmic front ends-one for photodiode current (INPT) and one for reference current (IREF)-enabling true log-ratio operation. Its internal temperature compensation eliminates kT/q drift via analog division of V_BE differences, yielding stable 200 mV/decade slope across −40°C to +85°C.

It integrates a rail-to-rail buffer amplifier (BFIN/SCAL/VOUT) with 15 MHz bandwidth and 25 mA drive capability, plus a 2.5 V reference output (VREF) with ±15 mV drift over temperature. The VSUM guard node maintains 0.5 V bias at INPT/IREF for photodiode anode interfacing without grounding constraints.

Key Specifications

Pinout & Package

AD8305ACP-R2 is housed in a 16-lead LFCSP (3 mm × 3 mm) with exposed thermal pad soldered to ground. Pin numbering follows top-view orientation per Figure 2 of Rev. C datasheet.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar logarithmic converter applications.

Compared with AD8305ACP-R2, AD8304ARUZ trades 40 dB range and on-chip VREF for smaller footprint and lower power, while MAX4206ETA+ offers lower cost but sacrifices 30 dB range and adds 0.6 dB law error-making AD8305ACP-R2 the sole choice for telecom-grade 100 dB optical power measurement.

Availability

AD8305ACP-R2 is available at Aetrix Electronics and suitable for fiber optic transceiver monitoring, optical spectrophotometry, and wide-dynamic-range current ratio metrology requiring stable component supply across extended temperature and lifecycle windows.

Supply support for AD8305ACP-R2 includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Analog Devices, Inc. is a global leader in high-performance analog, mixed-signal, and digital signal processing semiconductors, headquartered in Norwood, MA.

The AD8305ACP-R2 belongs to Analog Devices' precision logarithmic amplifier product line, designed specifically for fiber-optic supervisory systems requiring accurate, temperature-stable optical power measurement across five decades of current.

FAQ

What is the guaranteed dynamic range of the AD8305ACP-R2 over temperature?

The AD8305ACP-R2 guarantees 100 dB dynamic range (10 nA to 1 mA) at 25°C. Over the full −40°C to +85°C operating range, the minimum specified input current remains 10 nA and maximum remains 1 mA per Table 1, with law conformance error increasing to ±0.4 dB. Thus, AD8305ACP-R2 maintains its full 100 dB usable range across industrial temperature extremes.

Can the AD8305ACP-R2 operate with a negative supply, and what changes does it require?

Yes, the AD8305ACP-R2 supports optional dual supplies with VNEG (Pins 6/7) down to −5.5 V. When VN ≤ −0.5 V, the VSUM pin may be grounded, allowing INPT and IREF to operate at 0 V-enabling voltage-input configurations using series resistors. However, IREF resistor value must be adjusted to maintain intercept, and self-heating effects at high currents require derating per Absolute Maximum Ratings.

How is the logarithmic intercept of the AD8305ACP-R2 adjusted, and what is its default value?

The AD8305ACP-R2 logarithmic intercept is set by the external resistor R_REF between VREF (2.5 V) and IREF. With R_REF = 200 kΩ, IREF = 10 µA, yielding a nominal intercept of 1 nA. Adjusting R_REF scales IREF inversely: e.g., 2 MΩ gives 1 µA IREF and 100 pA intercept. This adjustment is fully supported across the 10 nA–1 mA IREF range per datasheet Table 1.

Does the AD8305ACP-R2 include an internal voltage reference, and how is it used?

Yes, the AD8305ACP-R2 provides a 2.5 V ±65 mV reference at Pin VREF, derived from an internal bandgap circuit. It serves two key roles: (1) generating the precise 10 µA IREF current via external 200 kΩ resistor, and (2) acting as ADC reference voltage to scale VLOG output for exact 10 mV/dB digitization-eliminating external reference ICs in optical power meter designs.

What is the function of the VSUM pin on the AD8305ACP-R2, and why is it critical for photodiode interfacing?

The VSUM pin on the AD8305ACP-R2 is a guard node held at 0.5 V to bias the INPT and IREF inputs. This allows photodiode anodes to float at 0.5 V-avoiding grounding conflicts in reverse-biased photodiode circuits. Its low-impedance, low-drift design (0.015 mV/°C) shields the picoamp-level current paths from PCB leakage and noise, directly enabling the AD8305ACP-R2's 10 nA minimum input specification.