Texas Instruments LOG100JP

Overview

LOG100JP from Texas Instruments (formerly Burr-Brown) is a precision logarithmic and log ratio amplifier IC designed for optical power monitoring, laser diode control, and EDFA subsystems. It delivers 0.37% FSO total error over six decades (1nA–1mA), ±10V output swing, and pin-selectable scale factors (1/3/5 V/decade) with internal laser-trimmed thin-film resistors.

For engineers reviewing the LOG100JP datasheet, LOG100JP pinout, LOG100JP application, or LOG100JP equivalent, this page provides verified technical context, real-world use cases in optical density measurement and absorbance computation, confirmed pin-level design meaning, and validated alternative options for log-ratio signal conditioning in telecom and instrumentation systems.

Technical Context

The LOG100JP implements a matched bipolar transistor pair-based log ratio architecture with FET-input amplifiers (1pA typical bias current) to support accurate current-mode operation down to 1nA. Its transfer function VOUT = K·log(I₁/I₂) is temperature-compensated via integrated thin-film resistors with positive TC matching VT drift.

Frequency compensation is externally set via capacitor between pins 7 and 14, with bandwidth ranging from 0.11 kHz (I₂ = 1nA) to 45 kHz (I₂ = 1mA). Input currents flow into pins 1 (I₁) and 14 (I₂); output appears at pin 9 with rail-to-rail ±10V capability and ±5mA drive strength.

Key Specifications

Pinout & Package

LOG100JP is housed in a 14-pin hermetic ceramic DIP package with metal lid internally connected to common (pin 10). The package provides high reliability for optical networking and industrial environments requiring long-term stability and moisture resistance.

Key Features

Applications

Equivalent & Alternatives

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

Compared with ADL5513ACPZ-R7 and LM13700N, LOG100JP uniquely integrates matched logging transistors, laser-trimmed resistors, and dual current inputs in a single hermetic package-enabling out-of-the-box 0.37% FSO accuracy for optical density and EDFA gain control without external components or firmware.

Availability

LOG100JP is available at Aetrix Electronics and suitable for optical networking infrastructure, laser diode control loops, and EDFA subsystems requiring stable component supply with long-lifecycle assurance.

Supply support for LOG100JP 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 acquired Burr-Brown in 2000 and maintains legacy high-precision analog product lines including the LOG100 series. TI specializes in high-reliability signal conditioning ICs for test, measurement, and industrial applications.

The LOG100 product line was engineered specifically for analog logarithmic computation in optical and analytical instrumentation-prioritizing guaranteed accuracy, low bias current, and ratiometric stability over general-purpose op-amp flexibility.

FAQ

What is the guaranteed total error specification for LOG100JP across its full input range?

The LOG100JP guarantees ±37 mV maximum total error at 1nA input, scaling linearly with scale factor K (e.g., ±111 mV at K = 3). This corresponds to 0.37% of full-scale output (±10 V) and is specified over the entire six-decade range (1nA to 1mA) at +25°C with ±15 V supplies after 15-minute warm-up. Temperature drift adds ±1.26 mV/°C at 1nA, contributing to worst-case error envelopes shown in the datasheet's Typical Performance Curves.

Can LOG100JP be used with voltage inputs instead of current inputs?

Yes, LOG100JP supports voltage inputs via external series resistors, but performance is limited to approximately three decades of dynamic range due to input offset voltage and noise effects. The transfer function becomes VOUT = K·log(V₁/R₁ ÷ V₂/R₂), requiring matched precision resistors. For best accuracy, current-mode operation using photodiodes or transimpedance amplifiers is strongly preferred-LOG100JP's 1 pA bias current and laser-trimmed resistors are optimized for that configuration.

How does LOG100JP achieve temperature-stable logarithmic performance?

LOG100JP achieves temperature stability through monolithic integration of matched bipolar logging transistors and thin-film resistors with precisely tailored positive temperature coefficients. These resistors compensate for the inherent VT = kT/q drift in the base-emitter junctions. The result is a log conformity temperature coefficient of just 0.001%/°C over six decades, enabling stable optical gain measurement in uncontrolled ambient environments without active oven control or digital correction.

What is the purpose of pin 2 (Scale Factor Trim) on LOG100JP?

Pin 2 on LOG100JP provides access to the internal scaling resistor network for fine adjustment of the K factor beyond the standard 1/3/5 V/decade selections. As shown in the datasheet's Figure 8, adding series or parallel resistors between pin 2 and pins 3/4/5 allows continuous K tuning-for example, achieving 2.2 V/decade for custom optical density calibration curves. This trim capability preserves the LOG100JP's guaranteed accuracy while enabling application-specific scaling without redesigning the signal chain.

Is LOG100JP suitable for driving capacitive loads such as ADC input capacitors?

LOG100JP maintains stable operation with capacitive loads up to 100 pF. For larger loads-including successive-approximation ADC input capacitances exceeding 100 pF-a 22 Ω carbon composition resistor must be placed in series with pin 9 (VOUT) to isolate the output stage. This series resistor prevents peaking or oscillation while introducing negligible gain error (<0.1%) given the LOG100JP's 0.05 Ω output impedance and typical ADC input impedances >1 MΩ.