Texas Instruments LOG101AIDG4

Overview

LOG101AIDG4 from Texas Instruments is a precision logarithmic and log ratio amplifier IC that computes VOUT = 1V × log(I₁/I₂) using matched bipolar transistor core architecture. It delivers 0.01% FSO log conformity over 5 decades (1nA–100µA), supports 7.5-decade dynamic input range (100pA–3.5mA), operates from ±4.5V to ±18V supplies, and is housed in an SO-8 package. It is used in photodiode signal compression, absorbance measurement, and front-end analog signal compression for A/D converters.

For engineers reviewing the LOG101AIDG4 datasheet, LOG101AIDG4 pinout, LOG101AIDG4 application, or LOG101AIDG4 equivalent, key selection criteria include log conformity error vs. temperature, compensation capacitor sizing for bandwidth control, input bias current impact on low-level accuracy, and dual-supply operational constraints in optical sensing systems.

Technical Context

The LOG101AIDG4 implements a true analog logarithmic transfer function based on the base-emitter voltage relationship of thermally matched bipolar transistors (Q1/Q2), with internal temperature compensation of VT = kT/q via a positive-TC resistor network. Its core operation requires two externally sourced input currents - I₁ and I₂ - with output scaled to 1V per decade of current ratio.

Frequency response is actively controlled by an external compensation capacitor (CC) connected between pins 3 and 8; bandwidth varies from 0.1kHz (I₂ = 10nA, CC = 4500pF) to 45kHz (I₂ = 1mA, CC = 50pF). Transient response differs for rising vs. falling inputs due to nonlinear gain characteristics, and negative input currents require external inversion circuitry.

Key Specifications

Pinout & Package

LOG101AIDG4 is packaged in an SOIC-8 (D package), 1.75 mm max height, RoHS-compliant, with NIPDAU lead finish and JEDEC MS-012 AA outline. Pin 1 is marked by a beveled corner or dot; device orientation follows standard SOIC quadrant assignment (Q1).

Key Features

Applications

Equivalent & Alternatives

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

Compared with ADL5513ACPZ-R7 and LM13700N, LOG101AIDG4 uniquely combines factory-trimmed 1V/decade scaling, 7.5-decade DC input range, and internal temperature compensation - making it the only option qualified for metrology-grade absorbance and photometric applications requiring <0.02% log conformity.

Availability

LOG101AIDG4 is available at Aetrix Electronics and suitable for photometric instrumentation, analytical sensor front-ends, medical oximetry modules, and industrial optical monitoring systems requiring stable component supply and long-lifecycle support.

Supply support for LOG101AIDG4 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

Texas Instruments is a global semiconductor leader specializing in analog, embedded processing, and high-reliability silicon solutions for industrial, automotive, and communications markets.

The LOG101 product line was designed specifically for precision DC logarithmic computation in analytical instrumentation, optical sensing, and sensor signal conditioning - emphasizing metrological accuracy over speed or integration density.

FAQ

What is the maximum input current the LOG101AIDG4 can handle without damage?

The LOG101AIDG4 has an absolute maximum input current rating of ±10mA per input (pins 1 and 8), but sustained operation above 3.5mA degrades log conformity and increases nonlinearity. For reliable 0.06% FSO accuracy across 7.5 decades, input currents must stay within 100pA to 3.5mA. Exceeding 3.5mA risks thermal overload of the internal logging transistors and invalidates the published total error specification. The LOG101AIDG4 datasheet explicitly states that input currents larger than 3.5mA result in increased nonlinearity and should be avoided in precision applications.

Can LOG101AIDG4 operate from a single +5V supply?

Yes, LOG101AIDG4 can operate from a single +5V supply using an external negative charge pump (e.g., TPS60402DBV) to generate the required –5V rail, as shown in Figure 10 of the SBOS242B datasheet. The device itself requires dual supplies (±4.5V to ±18V) and cannot function with only a single positive rail. Direct single-supply operation would violate the common-mode voltage range of its internal amplifiers (A1/A2), causing output saturation or undefined behavior. The LOG101AIDG4's input stage requires both rails to bias the matched transistor pair and maintain proper VBE operating points.

How does the compensation capacitor (CC) affect LOG101AIDG4 bandwidth and stability?

The compensation capacitor (CC), connected between pins 3 (GND) and 8 (V+), directly controls LOG101AIDG4 bandwidth and phase margin. Larger CC values improve stability but reduce bandwidth - e.g., 4500pF yields 0.1kHz BW at I₂ = 10nA, while 50pF enables 45kHz at I₂ = 1mA. The minimum recommended CC depends on I₁/I₂ extremes: select CC based on max I₂ and min I₁ to avoid oscillation. The LOG101AIDG4 datasheet provides "Minimum Value of Compensation Capacitor" curves showing CC vs. I₂ for fixed I₁. Incorrect CC sizing causes overshoot, ringing, or sustained oscillation at VOUT.

Is LOG101AIDG4 pin-compatible with earlier LOG101 variants like LOG101AID?

Yes, LOG101AIDG4 is a green (RoHS-compliant) variant of the LOG101AID, sharing identical SOIC-8 (D) package, pinout, electrical specifications, and thermal characteristics. The "G4" suffix denotes TI's lead-free/NIPDAU finish and qualifies the part for RoHS compliance; all functional parameters - including log conformity, supply range, and input range - match LOG101AID exactly. No PCB layout changes or schematic modifications are needed when substituting LOG101AIDG4 for LOG101AID in existing designs.

What is the role of the two NC pins (2 and 5) on LOG101AIDG4?

Pins 2 and 5 on LOG101AIDG4 are designated "No Internal Connection" - they are physically unbonded die pads with no electrical connection to the silicon. These pins must remain unconnected in the PCB layout; neither grounding nor routing is permitted. Connecting them may introduce parasitic capacitance or leakage paths that degrade input bias current performance (<5pA) or cause unpredictable offset drift. The LOG101AIDG4 datasheet explicitly warns against routing traces to NC pins, and TI's SOIC-8 package drawing confirms their isolation from internal circuitry.