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Texas Instruments LOG112AIDG4
- Part No.:
- LOG112AIDG4
- Manufacturer:
- Texas Instruments
- Category:
- Instrumentation, Op Amps, Buffer Amps
- Package:
- 14-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
LOG112AIDG4.pdf
- Description:
- IC LOG/LOG 1 CIRCUIT 14SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:3,026
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Product details
Overview
LOG112AIDG4 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 dual supply range, and SO-14 narrow package - used in absorbance measurement, photodiode signal compression, and front-end analog signal compression before A/D conversion.
For engineers reviewing the LOG112AIDG4 datasheet, LOG112AIDG4 pinout, LOG112AIDG4 application, or LOG112AIDG4 equivalent, key selection considerations include its 0.2% FSO log conformity over 5 decades, on-chip 2.5 V voltage reference, low 5 pA input bias current, –40°C to +85°C operating temperature, and compatibility with photodiode interfaces requiring wide dynamic range current-to-voltage logarithmic conversion.
Technical Context
The LOG112AIDG4 implements a true logarithmic transfer function using matched bipolar transistor pairs (Q1/Q2) and internal op amps (A1–A3) to realize VLOGOUT = (0.5 V)·log₁₀(I₁/I₂). Its core log circuitry is temperature-compensated via metal resistors and internal bandgap reference, enabling stable scaling across –5°C to +75°C specified range.
It integrates three functional blocks: a high-precision log ratio core (A1/A2/Q1/Q2), an output scaling amplifier (A3) with external gain-setting resistors R1/R2, and a 2.5 V bandgap voltage reference usable for generating precision reference currents. Input common-mode range extends to within 1.2 V of rails, and frequency compensation is externally set via capacitor CC between pins 5 and 14.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Log Scaling Factor | 0.5 V/decade - enables direct mV-per-decade readout without post-processing scaling |
| Input Dynamic Range | 100 pA to 3.5 mA (7.5 decades) - supports ultra-low-light photodiode signals up to industrial-level current sensing |
| Log Conformity Error | 0.2% FSO over 5 decades - ensures <±1 mV deviation from ideal log curve at mid-range currents |
| Supply Voltage Range | ±4.5 V to ±18 V - allows operation from low-power ±5 V systems to high-voltage industrial supplies |
| Input Bias Current | ±5 pA typical - minimizes loading error on high-impedance current sources like photodiodes |
| Voltage Reference | 2.5 V ±0.5% initial accuracy - provides stable reference for external RREF-based current generation |
| Quiescent Current | ±1.75 mA - balances precision performance with moderate power consumption in continuous operation |
Pinout & Package
LOG112AIDG4 is housed in a 14-pin SOIC (narrow) package (SO-14, package code D), with 1.27 mm pitch, JEDEC MS-012AC compliant, RoHS-compliant NIPDAU lead finish, MSL Level-3 rating, and thermal resistance θJA = 110°C/W.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 (I1) | Primary input current terminal | Accepts logarithmic input current I1; must be positive (conventional current into pin) |
| 2 (NC) | No internal connection | Not bonded; leave unconnected - no routing or grounding required |
| 3 (I2) | Reference input current terminal | Accepts fixed reference current I2; defines log ratio denominator in VLOGOUT = 0.5·log₁₀(I1/I2) |
| 4 (VCM – IN) | Common-mode input voltage pin | Applies bias to log transistors; improves accuracy at high input currents when set to +1 V to +2.5 V |
| 5 (VREF – GND) | Reference voltage output / ground reference | Provides 2.5 V bandgap reference; connect external RREF here to generate IREF |
| 6 (GND) | Analog ground reference | System ground return for internal circuitry; separate from power supply returns in sensitive layouts |
| 7 (V–) | Negative supply rail | Connects to negative supply (e.g., –5 V); powers all internal amplifiers and log core |
| 8 (VREF) | Internal reference voltage node | Internal tap of bandgap reference; not user-accessible - do not load or route |
| 9 (+IN3) | Inverting input of scaling op amp A3 | Used with external R1/R2 to scale VLOGOUT; connects to VLOGOUT for unity-gain buffer or gain configuration |
| 10 (–IN3) | Non-inverting input of scaling op amp A3 | Set to ground or reference for differential gain; enables programmable output scaling K = 1 + R2/R1 |
| 11 (VLOGOUT) | Main logarithmic output | Delivers 0.5 V/decade log ratio output; buffered, capable of driving ≥10 kΩ loads |
| 12 (V+) | Positive supply rail | Connects to positive supply (e.g., +5 V); powers all internal circuitry |
| 13 (VO3) | Scaled output of op amp A3 | Final amplified/log-ratio output; K × VLOGOUT where K is set by external R1/R2 |
| 14 (CC) | Frequency compensation capacitor terminal | Connect external capacitor (e.g., 120 pF to 4.5 nF) between pin 5 and pin 14 to stabilize bandwidth vs. input current level |
Key Features
| Feature | Design Value |
|---|---|
| On-chip 2.5 V voltage reference | Enables precise, temperature-stable reference current generation with single external resistor (RREF), eliminating need for external reference ICs |
| 0.5 V/decade log scaling | Directly maps 10× current change to 500 mV output shift - simplifies calibration and ADC interface design |
| 7.5-decade input range (100 pA–3.5 mA) | Supports single-device measurement from weak photodiode signals to high-current sensor outputs without range switching |
| Low 5 pA input bias current | Preserves signal integrity in high-impedance current-sensing paths, critical for photodiode and ionization chamber applications |
| Integrated scaling amplifier (A3) | Allows gain adjustment (K = 1 + R2/R1) of VLOGOUT without external op amp - reduces board space and component count |
Applications
| Absorbance Measurement | Photodiode Signal Compression |
|---|---|
Use Scenario: Measuring optical density of chemical samples using dual-wavelength light sources and matched photodetectors. IC Role / Device Role / Timing Role: LOG112AIDG4 computes log ratio of two photodiode currents (I₁/I₂) to directly yield absorbance A = log(I₁/I₂), rejecting common-mode intensity drift. Use Value: Eliminates need for digital division and floating-point math; achieves 0.2% FSO accuracy over 5 decades without system-level calibration. | Use Scenario: Compressing wide-dynamic-range photocurrent from a reverse-biased photodiode before feeding into a 12-bit ADC. IC Role / Device Role / Timing Role: LOG112AIDG4 acts as analog-domain compressor, converting 100 pA–1 mA photocurrent into 0–2.5 V logarithmic voltage. Use Value: Enables 12-bit ADC to resolve >100 dB dynamic range - equivalent to ~20-bit linear resolution - with no firmware overhead. |
| Analog Signal Compression Pre-A/D | Optical Density Measurement |
Use Scenario: Conditioning sensor outputs (e.g., gas sensors, radiation detectors) with exponential response characteristics prior to digitization. IC Role / Device Role / Timing Role: LOG112AIDG4 performs real-time analog log compression, reducing ADC resolution requirements and easing digital signal processing. Use Value: Reduces required ADC bits by ~3–4 bits while preserving signal fidelity; lowers system cost and power vs. oversampling + digital log computation. | Use Scenario: Quantifying turbidity or particle concentration in liquid media using transmitted light attenuation. IC Role / Device Role / Timing Role: LOG112AIDG4 computes log ratio of incident and transmitted photocurrents to output optical density OD = log(I₀/I). Use Value: Provides direct, temperature-stable OD readout with <0.01% log conformity error - meets ASTM E275 and ISO 7027 linearity requirements. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar logarithmic amplifier applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| ADL5513ACPZ-R7 | RF log detector (100 MHz–4 GHz), 65 dB dynamic range, DC-coupled only to 10 MHz; no on-chip reference; requires external bias network. | Designed for RF power measurement, not precision DC/low-frequency current ratio; unsuitable for photodiode or absorbance use cases. | Select only for RF envelope detection; not a functional substitute for LOG112AIDG4's DC-coupled, current-input log ratio capability. |
| LT1004CS8-2.5 | 2.5 V shunt voltage reference only - no log function, no inputs, no output scaling, no current handling capability. | Cannot perform log computation or current ratio; serves only as standalone reference source. | Use only as supplemental reference in hybrid designs; cannot replace LOG112AIDG4's integrated log + reference + amplifier functionality. |
Compared with ADL5513ACPZ-R7 and LT1004CS8-2.5, LOG112AIDG4 uniquely integrates precision DC current-input logarithmic ratio computation, on-chip 2.5 V reference, and scalable output amplifier in one SO-14 package - making it irreplaceable for analytical instrumentation, photodiode compression, and absorbance systems requiring sub-percent accuracy over 7.5 decades.
Availability
LOG112AIDG4 is available at Aetrix Electronics and suitable for absorbance measurement systems, photodiode signal conditioning, and analog front-end compression circuits requiring stable component supply, long-term lifecycle support, and traceable sourcing for medical and industrial instrumentation.
Supply support for LOG112AIDG4 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 company headquartered in Dallas, Texas, delivering analog and embedded processing solutions for industrial, automotive, and communications markets.
The LOG112AIDG4 belongs to TI's Precision Logarithmic Amplifier product line, designed specifically for high-accuracy current-ratio computation in analytical instrumentation, optical sensing, and scientific measurement systems where wide dynamic range and temperature stability are critical.
FAQ
What is the primary function of the LOG112AIDG4?
The LOG112AIDG4 is a precision logarithmic amplifier IC that computes the base-10 logarithm of the ratio of two input currents (I₁/I₂), delivering VLOGOUT = (0.5 V)·log₁₀(I₁/I₂). It is optimized for DC and low-frequency applications including absorbance measurement, photodiode signal compression, and analog signal conditioning before A/D conversion. Its core function relies on matched bipolar transistor pairs and internal op amps - not digital computation.
Does the LOG112AIDG4 support single-supply operation?
The LOG112AIDG4 is designed for dual-supply operation (±4.5 V to ±18 V) and does not natively support true single-supply use. However, TI Application Note SBOS246D shows a workaround using an external charge pump (e.g., TPS60402DBV) to generate a negative rail from +5 V, enabling single +5 V system integration. Direct +5 V-only operation is not supported due to internal biasing requirements of the log transistor pair.
What is the role of the VCM pin on the LOG112AIDG4?
The VCM pin (Pin 4) on the LOG112AIDG4 applies a common-mode voltage to the log transistor bases, lifting them out of saturation at high input currents. When biased between +1 V and +2.5 V (e.g., from the on-chip 2.5 V reference), VCM reduces total output error from up to 25% to ~10% for inputs near 3.5 mA. It also enables photodiode cathode connection to avoid forward biasing - critical in optical measurement configurations.
Can the LOG112AIDG4 accept voltage inputs directly?
The LOG112AIDG4 is optimized for current inputs and does not accept voltage inputs directly. Voltage signals must be converted to current using series resistors; however, this limits effective dynamic range to ~3 decades due to voltage noise and offset errors. For best accuracy, TI recommends using external transimpedance amplifiers or precision current sources to drive I₁ and I₂ pins with controlled current - not voltage.
How is frequency compensation implemented on the LOG112AIDG4?
Frequency compensation for the LOG112AIDG4 is implemented by connecting an external capacitor (CC) between Pin 5 (VREF–GND) and Pin 14 (CC). Capacitor value depends on input current magnitude: 120 pF for 10 nA–100 nA, 375 pF for 1 µA–100 µA, and 950 pF for 1 µA–1 mA. Larger values improve stability but reduce bandwidth; TI provides minimum CC curves in SBOS246D Figure 6 to balance speed and accuracy per application.
LOG112AIDG4 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- -
- Package/Case:
- 14-SOIC (0.154", 3.90mm Width)
- Packaging:
- Tube
- Product Status:
- Obsolete
- Amplifier Type:
- Logarithmic and Log Ratio
- Number of Circuits:
- 1
- Output Type:
- -
- Slew Rate:
- 0.5V/µs
- Gain Bandwidth Product:
- 1.4 MHz
- -3db Bandwidth:
- 45 kHz
- Current - Input Bias:
- 5 pA
- Voltage - Input Offset:
- 300 µV
- Current - Supply:
- 1.25mA
- Current - Output / Channel:
- -
- Voltage - Supply Span (Min):
- 9 V
- Voltage - Supply Span (Max):
- 36 V
- Operating Temperature:
- -5°C ~ 75°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 14-SOIC
LOG112AIDG4 FAQ
1.How can I place an order for LOG112AIDG4 through Aetrix?
Please submit a Request for Quotation (RFQ) for LOG112AIDG4 on Aetrix. Our sales agent will provide a competitive quotation and guide you through the order confirmation once you accept the terms.
2.Are the price and stock information for LOG112AIDG4 reliable?
The price and inventory of LOG112AIDG4 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LOG112AIDG4 is usually 5 days.
3.What payment methods are accepted for LOG112AIDG4?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LOG112AIDG4 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LOG112AIDG4?
LOG112AIDG4 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LOG112AIDG4 order is processed, you will receive an email with the shipment details and tracking number.
Note: Tracking information may take up to 24 hours to appear. Express delivery typically takes 3–5 business days.
5.How can I obtain technical support or documentation for LOG112AIDG4?
For technical support, including LOG112AIDG4 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LOG112AIDG4 requirements.
6.How does Aetrix verify that LOG112AIDG4 is sourced from the original manufacturer or authorized distributors?
All LOG112AIDG4 products on Aetrix are procured from qualified distributors and authorized channels. Our dedicated quality assurance team conducts strict verification, including traceability checks and, if necessary, third-party testing. This ensures that LOG112AIDG4 meets industry standards.
7.What is the process for return or replacement of LOG112AIDG4?
All LOG112AIDG4 units undergo pre-shipment inspection (PSI). If there is an issue with LOG112AIDG4, returns or replacements are accepted under the following conditions:
1.Quantity discrepancies, incorrect items, or visible external defects (such as breakage or corrosion), acknowledged by Aetrix.
2.The issue is reported within 90 days of delivery.
3.The LOG112AIDG4 part is unused and in its original packaging.
Return procedure for LOG112AIDG4:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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