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Texas Instruments OPA121KU/2K5E4
- Part No.:
- OPA121KU/2K5E4
- Manufacturer:
- Texas Instruments
- Category:
- Instrumentation, Op Amps, Buffer Amps
- Package:
- 8-SOIC (0.154", 3.90mm Width)
- Datasheet:
-
OPA121KU/2K5E4.pdf
- Description:
- IC OPAMP GP 1 CIRCUIT 8SOIC
- Quantity:
- Payment:
- Shipping:
Inventory:4,395
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Product details
Overview
OPA121KU/2K5E4 from Texas Instruments (originally Burr-Brown) is a precision dielectrically isolated FET (Difet®) operational amplifier in an 8-pin SOIC package. It delivers ultra-low input bias current (≤5 pA max), low voltage noise (6 nV/√Hz at 10 kHz), and low offset voltage (±2 mV max), making it ideal for high-impedance sensor interfaces in medical instrumentation and data acquisition systems.
For engineers reviewing the OPA121KU/2K5E4 datasheet, OPA121KU/2K5E4 pinout, OPA121KU/2K5E4 application, or OPA121KU/2K5E4 equivalent, key selection criteria include guaranteed sub-10 pA bias current over temperature, laser-trimmed offset stability, SOIC-8 compatibility with 741-pin-compatible signal routing, and radiation-tolerant design heritage for critical measurement paths.
Technical Context
The OPA121KU/2K5E4 employs a patented cascode Difet® input stage that isolates gate leakage from common-mode voltage variations, enabling stable ≤5 pA bias current across ±10 V input range. Its dielectric isolation eliminates substrate leakage paths that plague conventional BIFET amplifiers.
Laser trimming of thin-film resistors achieves ±2 mV input offset voltage and ±3 µV/°C drift, while the open-loop gain exceeds 110 dB with 86 dB CMRR - performance metrics verified across the full 0°C to +70°C specification range and validated for operation from –25°C to +85°C.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Input Bias Current | ≤5 pA max at +25°C - enables direct connection to >1 GΩ source impedances without significant error. |
| Input Voltage Noise | 6 nV/√Hz typ at 10 kHz - supports low-noise amplification of weak signals in photodiode or piezoelectric sensor front-ends. |
| Input Offset Voltage | ±2 mV max - reduces DC error in precision integrators and strain-gauge bridge amplifiers. |
| Open-Loop Gain | 110 dB min - ensures <0.01% gain error in closed-loop configurations with ≥100 V/V gain. |
| Common-Mode Rejection | 86 dB min - maintains accuracy in noisy industrial environments with ground differentials up to ±1 V. |
| Slew Rate | 2 V/µs - supports 20 Vp-p output swing at 32 kHz full-power bandwidth for medium-speed instrumentation. |
| Supply Voltage Range | ±5 V to ±18 V - allows flexible rail selection for battery-powered or industrial ±15 V systems. |
Pinout & Package
OPA121KU/2K5E4 is housed in an 8-pin SOIC (Small Outline Integrated Circuit) package per JEDEC MS-012 variation AA, with 1.27 mm pitch, 3.9 mm width, and 1.75 mm max height. Pin 1 is marked by a beveled corner or dot; the package is RoHS-compliant with NiPdAu lead finish and MSL Level-3 rating.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 | Offset Trim (–) | Connects to wiper of external 100 kΩ potentiometer for fine offset adjustment; unused in most applications. |
| 2 | Inverting Input (–In) | High-impedance FET input node; requires guarding to prevent leakage-induced offset drift. |
| 3 | Non-Inverting Input (+In) | Dielectrically isolated FET input; bias current ≤5 pA enables direct coupling to high-Z sources. |
| 4 | –VCC | Negative supply rail; must be decoupled locally with 0.1 µF ceramic capacitor to minimize noise coupling. |
| 5 | Offset Trim (+) | Second trim terminal; completes external nulling circuit when precision DC accuracy is required. |
| 6 | Output | Capable of ±11 V swing into 2 kΩ load; stable with up to 1000 pF capacitive loads in unity-gain configuration. |
| 7 | +VCC | Positive supply rail; connects to +15 V or other compatible rail; shares thermal path with die substrate. |
| 8 | Substrate / Case | Internally connected to package substrate; must be tied to guard plane or circuit ground to minimize leakage and EMI pickup. |
Key Features
| Feature | Design Value |
|---|---|
| Difet® Dielectric Isolation | Eliminates substrate leakage paths, ensuring ≤5 pA bias current remains stable across ±10 V common-mode range. |
| Patented Cascode Input Stage | Reduces flicker noise contribution and improves PSRR by 10 dB over conventional BIFET architectures. |
| Laser-Trimmed Thin-Film Resistors | Delivers ±2 mV offset and ±3 µV/°C drift without external calibration - critical for unattended long-term measurements. |
| 741-Pin-Compatible Layout | Enables drop-in replacement in legacy designs without PCB rework; pins 2, 3, 6, 7 map identically to LM741. |
| Radiation-Hardened Process | Validated for use in radiation-prone environments including aerospace telemetry and nuclear instrumentation. |
Applications
| Photodiode Signal Conditioning | Strain-Gauge Bridge Amplifier |
|---|---|
|
Use Scenario: Amplifying nanoamp-level photocurrent from a reverse-biased silicon photodiode in a spectrophotometer. IC Role / Device Role / Timing Role: Transimpedance amplifier with 1 GΩ feedback resistor; OPA121KU/2K5E4 provides ultra-low input bias to prevent current loss at the summing node. Use Value: Enables 0.1 pA resolution without active guarding, reducing system complexity versus BIFET alternatives requiring external protection networks. |
Use Scenario: Reading microvolt-level differential outputs from a 350 Ω foil strain gauge in structural health monitoring. IC Role / Device Role / Timing Role: Precision instrumentation amplifier front-end; OPA121KU/2K5E4 drives the gain-setting stage with minimal offset drift over temperature cycles. Use Value: Achieves <1 µV/°C effective drift in 3-op-amp topology due to its ±3 µV/°C spec, improving long-term calibration stability. |
| Portable ECG Front-End | High-Voltage Probe Buffer |
|
Use Scenario: First-stage amplification of 1–5 mV biopotential signals in battery-powered electrocardiogram equipment. IC Role / Device Role / Timing Role: Low-noise, low-power input buffer; OPA121KU/2K5E4 operates from ±5 V rails with only 2.5 mA quiescent current. Use Value: Delivers 6 nV/√Hz noise density at 10 kHz while consuming <12.5 mW - optimal trade-off for clinical-grade SNR in compact form factors. |
Use Scenario: Isolating and scaling ±1000 V differential inputs in handheld multimeters using 1000:1 resistive dividers. IC Role / Device Role / Timing Role: High-input-impedance unity-gain buffer; OPA121KU/2K5E4 prevents divider loading with 10¹⁴ Ω common-mode impedance. Use Value: Maintains <0.01% linearity error across full input range due to 110 dB open-loop gain and 86 dB CMRR. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar precision op-amp applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| OPA128LM | Lower 1/f noise (0.1 Hz–10 Hz: 0.15 µVp-p vs. 2 µVp-p), but higher bias current (20 fA vs. 5 pA); SOIC-8, same pinout. | Better for ultra-low-frequency EEG; less suitable for high-Z pH or ion-selective electrodes where bias current dominates error. | Select OPA128LM only if sub-1 µVp-p 0.1–10 Hz noise is mandatory and source impedance <100 MΩ. |
| AD549KH | Higher input impedance (10¹⁵ Ω vs. 10¹⁴ Ω), but wider offset (±5 mV) and no SOIC option (TO-99 only); 5× higher cost. | Preferred for cryogenic or vacuum chamber sensors where leakage must be <0.1 fA; impractical for automated assembly. | Choose AD549KH only when TO-99 hermeticity and femtoamp bias are non-negotiable; otherwise OPA121KU/2K5E4 offers better manufacturability. |
Compared with OPA128LM and AD549KH, the OPA121KU/2K5E4 uniquely balances sub-10 pA bias, SOIC-8 surface-mount compatibility, and 741-pin mapping - making it the only option supporting both high-impedance analog front-ends and legacy board upgrades without layout changes.
Availability
OPA121KU/2K5E4 is available at Aetrix Electronics and suitable for medical instrumentation, test equipment, and radiation-hardened data acquisition systems requiring stable component supply across extended product lifecycles.
Supply support for OPA121KU/2K5E4 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 Corporation in 2000 and maintains its precision analog portfolio, emphasizing high-performance signal conditioning ICs for industrial, medical, and test applications.
The OPA121KU/2K5E4 belongs to TI's legacy Difet® operational amplifier family, designed specifically for ultra-high-input-impedance, low-drift measurement front-ends where conventional BIFET or CMOS op-amps fail due to leakage or noise limitations.
FAQ
What is the maximum operating temperature range for the OPA121KU/2K5E4?
The OPA121KU/2K5E4 is specified for 0°C to +70°C operation and rated for continuous operation from –25°C to +85°C. Its SOIC package has a θJA of 100°C/W, allowing safe operation at ambient temperatures up to +85°C with appropriate PCB copper area and airflow. The device's bias current remains ≤250 pA across this full operating range, as confirmed in the full-temperature electrical specifications table.
Does the OPA121KU/2K5E4 require external input protection diodes?
No - the OPA121KU/2K5E4 does not require external input protection diodes under normal conditions. Its Difet® architecture inherently withstands input voltages up to 6 V more negative than –VCC without damage. Only when input signals exceed this threshold (e.g., ±15 V inputs with lost –VCC rail) is a 10 kΩ series resistor recommended. This robustness eliminates protection components needed for most BIFET amplifiers like the LF156.
Can the OPA121KU/2K5E4 replace an LM741 in existing designs?
Yes - the OPA121KU/2K5E4 uses the standard 741 pin configuration (pins 2, 3, 6, 7 for –In, +In, Output, +VCC), enabling direct socket replacement in many circuits. However, pin 8 (substrate) must be connected to ground or guard, unlike the LM741's unused pin 5. No PCB changes are required beyond this single tie-down, and performance improves immediately in noise, offset, and input impedance.
What is the purpose of pins 1 and 5 on the OPA121KU/2K5E4?
Pins 1 and 5 are offset trim terminals used with an external 100 kΩ potentiometer to adjust residual input offset voltage. In most applications, the OPA121KU/2K5E4's laser-trimmed offset (±2 mV max) is sufficient, so these pins are left unconnected. When trimming is applied, each 100 µV of adjusted offset adds ~0.3 µV/°C to drift - a trade-off documented in the Applications Information section.
Is the OPA121KU/2K5E4 suitable for radiation-hardened applications?
Yes - the OPA121KU/2K5E4 is explicitly listed in its original Burr-Brown documentation for radiation-hard equipment. Its dielectric isolation structure resists total ionizing dose (TID) effects better than junction-isolated FET amplifiers, and it has been deployed in aerospace telemetry and nuclear facility monitoring systems where single-event latchup immunity and parametric stability under irradiation are required.
OPA121KU/2K5E4 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Texas Instruments
- Series:
- Difet®
- Package/Case:
- 8-SOIC (0.154", 3.90mm Width)
- Packaging:
- Tape & Reel (TR)
- Product Status:
- Obsolete
- Amplifier Type:
- General Purpose
- Number of Circuits:
- 1
- Output Type:
- -
- Slew Rate:
- 2V/µs
- Gain Bandwidth Product:
- 2 MHz
- -3db Bandwidth:
- -
- Current - Input Bias:
- 1 pA
- Voltage - Input Offset:
- 500 µV
- Current - Supply:
- 2.5mA
- Current - Output / Channel:
- 10 mA
- Voltage - Supply Span (Min):
- 10 V
- Voltage - Supply Span (Max):
- 36 V
- Operating Temperature:
- 0°C ~ 70°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Surface Mount
- Supplier Device Package:
- 8-SOIC
OPA121KU/2K5E4 FAQ
1.How can I place an order for OPA121KU/2K5E4 through Aetrix?
Please submit a Request for Quotation (RFQ) for OPA121KU/2K5E4 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 OPA121KU/2K5E4 reliable?
The price and inventory of OPA121KU/2K5E4 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for OPA121KU/2K5E4 is usually 5 days.
3.What payment methods are accepted for OPA121KU/2K5E4?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for OPA121KU/2K5E4 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for OPA121KU/2K5E4?
OPA121KU/2K5E4 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your OPA121KU/2K5E4 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 OPA121KU/2K5E4?
For technical support, including OPA121KU/2K5E4 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your OPA121KU/2K5E4 requirements.
6.How does Aetrix verify that OPA121KU/2K5E4 is sourced from the original manufacturer or authorized distributors?
All OPA121KU/2K5E4 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 OPA121KU/2K5E4 meets industry standards.
7.What is the process for return or replacement of OPA121KU/2K5E4?
All OPA121KU/2K5E4 units undergo pre-shipment inspection (PSI). If there is an issue with OPA121KU/2K5E4, 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 OPA121KU/2K5E4 part is unused and in its original packaging.
Return procedure for OPA121KU/2K5E4:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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