Texas Instruments LOG112AIDR

Overview

LOG112AIDR from Texas Instruments is a precision logarithmic amplifier IC that computes the logarithm or log ratio of input current I1 relative to reference current I2, with VLOGOUT trimmed to 0.5 V per decade over 7.5 decades (100 pA to 3.5 mA), ±1.75 mA quiescent current, ±4.5 V to ±18 V supply range, and SOIC-14 package - used in absorbance measurement, photodiode signal compression, and front-end analog signal compression before A/D conversion.

For engineers reviewing the LOG112AIDR datasheet, LOG112AIDR pinout, LOG112AIDR application, or LOG112AIDR equivalent, key selection criteria include confirmed log conformity error (0.13% over 7.5 decades), on-chip 2.5 V voltage reference accuracy (±0.5%), temperature drift of log output (±0.005 %/°C), and verified SOIC-14 pin compatibility for dual-supply instrumentation designs.

Technical Context

The LOG112AIDR implements a bipolar transistor-based logarithmic core using matched Q1/Q2 pairs and internal compensation to achieve high-accuracy log(I1/I2) computation. Its transfer function VLOGOUT = (0.5 V)·log₁₀(I1/I2) is factory-trimmed and stabilized by on-die metal resistors for temperature-invariant gain scaling.

It integrates three functional blocks: a precision log-ratio core (A1/A2), an output scaling amplifier (A3) with programmable gain via external R1/R2, and a 2.5 V bandgap voltage reference usable for generating stable reference currents - all operating within –40°C to +85°C junction temperature range with ESD-sensitive handling requirements.

Key Specifications

Pinout & Package

LOG112AIDR is housed in a narrow-body SOIC-14 (D) package with 1.27 mm pitch, JEDEC MS-012 compliant, RoHS-compliant NiPdAu lead finish, MSL Level-3 rating, and thermal resistance θ_JA = 110°C/W.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ADL5513ACPZ-R7 and LOG2112AIDWR, LOG112AIDR uniquely combines DC-precision log-ratio computation, on-chip 2.5 V reference, and SOIC-14 compactness - making it the only viable option for calibrated, low-frequency, single-channel absorbance or photodiode compression where RF bandwidth is irrelevant and board space is constrained.

Availability

LOG112AIDR is available at Aetrix Electronics and suitable for absorbance measurement systems, photodiode signal conditioning circuits, and analog front-ends for analytical instrumentation requiring stable component supply, long-term calibration integrity, and industrial temperature range support.

Supply support for LOG112AIDR 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 components for industrial, automotive, and communications markets.

The LOG112AIDR belongs to TI's precision analog amplifier product line, engineered specifically for high-accuracy logarithmic signal processing in analytical instrumentation, optical sensing, and scientific measurement systems where decades-spanning dynamic range and temperature-stable transfer functions are mandatory.

FAQ

What is the maximum input current the LOG112AIDR can handle without performance degradation?

The LOG112AIDR maintains specified accuracy up to 3.5 mA per input (I1 or I2). Input currents exceeding 3.5 mA increase nonlinearity; absolute maximum rating is 10 mA to prevent transistor damage. For 4.5 mA inputs on ±5 V supplies, total error rises to ~15–25%, mitigated by applying +1 V to +2.5 V to the VCM pin. LOG112AIDR datasheet Section "INPUT CURRENT RANGE" confirms this limit.

Does the LOG112AIDR support single-supply operation?

Yes - LOG112AIDR can operate from a single +5 V supply using a charge-pump negative rail generator (e.g., TPS60402DBV) to create a virtual ground, as shown in Figure 11 of the SBOS246D datasheet. The device requires both positive and negative rails for full specification compliance, but single-supply adaptation is validated and documented for portable instrumentation.

How is the 2.5 V reference used to generate a precision reference current in the LOG112AIDR?

The LOG112AIDR's VREF pin delivers a 2.5 V ±0.5% bandgap voltage. Connecting an external resistor RREF between VREF and I2 sets IREF = 2.5 V / RREF. For example, a 250 MΩ resistor yields 10 nA IREF. TI recommends using the T-network in Figure 4 to reduce resistor size and mitigate offset errors from A1's ±1.5 mV input offset. This method is integral to LOG112AIDR's log-ratio accuracy.

What compensation capacitor value should be used for the LOG112AIDR at 1 µA input current?

For I2 = 1 µA, the LOG112AIDR requires CC = 150 pF to achieve 38 kHz 3dB bandwidth, per Typical Characteristics curve "MINIMUM VALUE OF COMPENSATION CAPACITOR". The capacitor connects between pins 5 (VLOGOUT) and 14 (CC). Larger values improve stability but reduce bandwidth; smaller values risk oscillation. LOG112AIDR's frequency response is explicitly current-dependent per SBOS246D Table "FREQUENCY RESPONSE, CORE LOG".

Can the LOG112AIDR process negative input currents?

No - LOG112AIDR accepts only positive input currents (conventional current flowing into I1 or I2 pins). To handle negative currents, TI provides external inversion circuits using op amps and transistors (Figures 6–8 in SBOS246D). These add complexity and error sources; LOG112AIDR itself does not support bidirectional current logging in its native configuration.