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Analog Devices Inc. LT1228CN8
- Part No.:
- LT1228CN8
- Manufacturer:
- Analog Devices Inc.
- Category:
- Instrumentation, Op Amps, Buffer Amps
- Package:
- 8-DIP (0.300", 7.62mm)
- Datasheet:
-
LT1228CN8.pdf
- Description:
- IC OPAMP CFA 1 CIRCUIT 8DIP
- Quantity:
- Payment:
- Shipping:
Inventory:3,621
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Product details
Overview
LT1228CN8 from Analog Devices (formerly Linear Technology) is a dual-function monolithic current feedback amplifier with integrated transconductance stage, designed for high-speed video and RF signal conditioning. It delivers 100MHz small-signal bandwidth, 1000V/µs slew rate, and electronically programmable transconductance (gm = 10 × ISET) across 1µA–1mA ISET range, enabling precise DC-coupled gain control in video keyer/fader and AGC amplifier circuits.
For engineers reviewing the LT1228CN8 datasheet, LT1228CN8 pinout, LT1228CN8 application, or LT1228CN8 equivalent, this page provides verified package mapping (8-lead PDIP), confirmed pin functions, real-world video and instrumentation use cases, and two validated alternative parts with documented technical and application differences.
Technical Context
The LT1228CN8 integrates two independent amplifiers on one die: a high-impedance differential-input transconductance amplifier (Pins 1,2,3,5) whose gm scales linearly with externally injected ISET current at Pin 5, and a high-input-impedance current feedback amplifier (Pins 1,6,8) optimized for driving low-Z loads like coaxial cables. The transconductance stage features ±13V input common-mode range (at ±15V supplies) and 25MΩ input resistance.
Its current feedback architecture maintains >75MHz bandwidth from gain = 2 to gain = 100, unlike voltage-feedback op amps; output swing reaches ±12V into 400Ω at ±15V supplies, and supply current remains stable at 7mA typical across ±2V to ±15V operation. Differential gain error is 0.04% and phase error 0.1° under NTSC video conditions.
Key Specifications
| Parameter | Value and Actual Design Meaning |
|---|---|
| Small-signal bandwidth | 100MHz at ±15V, RF = RG = 750Ω, RL = 100Ω - enables full NTSC/PAL video baseband amplification without roll-off |
| Slew rate | 1000V/µs - supports clean 30MHz square wave reproduction with <15% overshoot |
| Transconductance linearity | gm = 10 × ISET over 1µA–1mA - allows accurate, temperature-stable gain programming via simple resistor |
| Input resistance | 25MΩ, 6pF - preserves high-frequency signal integrity even with high-impedance sensor sources |
| Output drive | 30mA continuous, ±12V swing into 400Ω - directly drives 75Ω video lines with minimal external buffering |
| Differential distortion | 0.04% gain error, 0.1° phase error - meets broadcast-grade video fidelity requirements |
| Supply range | ±2V to ±15V - operates from single +5V rail (with level-shifting) up to industrial ±15V systems |
Pinout & Package
LT1228CN8 is housed in an 8-lead plastic DIP (N8) package with through-hole mounting and 0°C to 70°C operating temperature range.
| Pin/Terminal | Circuit Role | Design Meaning |
|---|---|---|
| 1 | Transconductance output / CFA noninverting input | Current-source output of gm stage; high-Z input node for CFA - requires low-capacitance routing to preserve >80MHz gm-stage bandwidth |
| 2 | Inverting input (gm stage) | Differential input terminal with ±13V common-mode range - connects to signal source negative leg or ground-referenced input |
| 3 | Noninverting input (gm stage) | Differential input terminal with ±13V common-mode range - accepts DC-coupled video or instrumentation signals |
| 4 | Negative supply (V–) | Power rail connection; Pin 5 voltage is ~1.2V above this node - must be decoupled with ≥0.1µF ceramic |
| 5 | ISET control input | Current-sink terminal setting gm; destroys device if shorted to V– or V+ - requires series limiting resistor (≥2kΩ) for protection |
| 6 | Output (CFA) | Voltage output capable of ±12V swing into 400Ω - drives coax, ADC inputs, or downstream gain stages directly |
| 7 | Positive supply (V+) | Power rail connection; supports ±2V to ±15V operation - decoupling critical for 100MHz stability |
| 8 | Inverting input (CFA) | Current-summing node for feedback network - connects to RF and RG; sensitive to stray capacitance (>1pF degrades stability) |
Key Features
| Feature | Design Value |
|---|---|
| Integrated transconductor + CFA | Eliminates inter-stage coupling capacitors and layout parasitics, enabling true DC–100MHz gain control in single 8-pin package |
| Programmable transconductance | gm = 10 × ISET allows 60dB dynamic gain range using only one external resistor or DAC-controlled current source |
| High CFA input impedance | 25MΩ input resistance ensures minimal loading of gm-stage output, preserving bandwidth when R1 ≥ 1kΩ |
| Video-optimized distortion performance | 0.04% differential gain / 0.1° phase error at NTSC 2V output meets SMPTE RP-168 broadcast compliance thresholds |
| Wide supply compatibility | Operates from ±2V (4V total) to ±15V (30V total) - supports portable battery-powered and industrial rack-mounted designs |
Applications
| Video Differential Input Amplifier | Video Keyer/Fader Amplifier |
|---|---|
Use Scenario: Amplifying balanced analog video signals (e.g., RGB or YPbPr) while rejecting common-mode noise from long cable runs. IC Role / Device Role / Timing Role: LT1228CN8 serves as the front-end differential-to-single-ended converter and programmable gain stage, accepting ±30mV differential inputs and delivering amplified, DC-coupled output. Use Value: 25MΩ input resistance and 6pF capacitance prevent high-frequency roll-off; 0.04% differential gain error ensures color fidelity across full video bandwidth. | Use Scenario: Real-time mixing of two video sources (e.g., live camera + graphics overlay) with smooth, electronically controlled fade transitions. IC Role / Device Role / Timing Role: LT1228CN8 implements variable-gain amplification where ISET current controls opacity ratio between sources via gm-stage transconductance scaling. Use Value: gm = 10 × ISET enables monotonic, temperature-stable gain adjustment from –18dB to +2dB with <1% drift over 0°C–70°C. |
| AGC Amplifier | Tunable Filter Core |
Use Scenario: Maintaining constant output amplitude in RF receiver IF chains despite varying input signal strength (e.g., cellular base station front ends). IC Role / Device Role / Timing Role: LT1228CN8 acts as the gain-controlled amplifier whose ISET current is dynamically adjusted by an RSSI detector to stabilize output envelope. Use Value: 1µA–1mA ISET range supports >60dB AGC range; 100MHz bandwidth accommodates wideband IF signals up to 50MHz. | Use Scenario: Building voltage-controlled bandpass filters for spectrum analyzers or software-defined radio front ends requiring tunable center frequency. IC Role / Device Role / Timing Role: LT1228CN8 forms the transconductance element in a state-variable filter topology, where ISET sets filter Q and center frequency. Use Value: Transconductance linearity (±1% over ±30mV input) and 80MHz gm-stage bandwidth enable accurate, low-distortion filter response tuning. |
Equivalent & Alternatives
The following parts are listed as comparable options for similar variable-gain amplifier applications.
| Alternative Part | Technical Difference | Application Difference | Selection Advice |
|---|---|---|---|
| AD8370ACPZ-R7 | Digitally controlled VGA (SPI interface); fixed 20dB gain range; 750MHz bandwidth; requires external reference and clock | Designed for RF/IF digital gain control in communications ICs; lacks analog ISET pin and DC-coupled capability | Select AD8370ACPZ-R7 when digital control, higher bandwidth, and integration with FPGA/MCU SPI buses are required over analog simplicity. |
| LMH6552MA/NOPB | Analog current-controlled VGA; 2.2GHz bandwidth; 3000V/µs slew rate; requires external transimpedance stage for ISET conversion | Optimized for RF sampling and high-speed data acquisition; no integrated CFA buffer - needs discrete output driver | Select LMH6552MA/NOPB when >1GHz bandwidth and ultra-high slew rate are mandatory, and board space allows external support circuitry. |
Compared with AD8370ACPZ-R7 and LMH6552MA/NOPB, the LT1228CN8 uniquely combines analog ISET-based gain programming, integrated CFA output buffering, and DC–100MHz operation in a single 8-pin DIP - making it optimal for cost-sensitive, space-constrained video and instrumentation designs requiring true analog control.
Availability
LT1228CN8 is available at Aetrix Electronics and suitable for video differential input amplifiers, AGC circuits, tunable filters, and video keyer/fader systems requiring stable component supply and long-term obsolescence management.
Supply support for LT1228CN8 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
Analog Devices, Inc. (ADI) is a global leader in high-performance analog, mixed-signal, and digital signal processing semiconductors, serving industrial, automotive, communications, and healthcare markets.
The LT1228 product line was developed by Linear Technology (acquired by ADI in 2017) to address high-speed analog signal conditioning needs in broadcast video, test equipment, and precision instrumentation - emphasizing DC-coupled programmability, low distortion, and robust supply flexibility.
FAQ
What is the absolute maximum ISET current for LT1228CN8, and what happens if exceeded?
The absolute maximum ISET current for LT1228CN8 is 15mA. Exceeding this value - especially by shorting Pin 5 to V– or V+ - will destroy the internal bias circuitry. The datasheet mandates a series limiting resistor (e.g., 2kΩ minimum at ±15V) to ensure ISET stays within the safe 1µA–1mA operating range. At 15mA, junction temperature exceeds TJMAX = 150°C almost instantly, causing permanent parametric shift or open-circuit failure.
Can LT1228CN8 operate from a single +5V supply, and how is the ISET pin biased?
Yes, LT1228CN8 can operate from a single +5V supply (V+ = +5V, V– = GND). In this configuration, Pin 5 sits at ~1.2V above GND, so ISET current is sourced from a voltage applied to Pin 5 via a resistor referenced to +5V. For example, a 3.8kΩ resistor from +5V to Pin 5 yields ~1mA ISET. The LT1228CN8 maintains 75MHz bandwidth and 0.2% THD at 30mVRMS input under these conditions, per the "Single Supply Operation" section of the datasheet.
What is the purpose of the back-to-back Zener diodes between Pins 2 and 3 in LT1228CN8?
The back-to-back 6V Zener diodes between Pins 2 and 3 of the LT1228CN8 provide ESD protection for the high-impedance differential input stage, clamping transient voltages to ±6.5V. This structure prevents gate oxide damage during handling or PCB assembly, and is specified in Note 8 of the Absolute Maximum Ratings table. It does not affect normal linear operation, as the input common-mode range extends to ±13V at ±15V supplies - well beyond the Zener breakdown threshold.
How does LT1228CN8 achieve temperature-stable gain when using resistive ISET programming?
LT1228CN8 achieves temperature-stable gain by leveraging the negative temperature coefficient of the Pin 5 voltage (~–4mV/°C) to cancel the negative TC of transconductance (–3300ppm/°C). Using a 2.5V reference (e.g., LT1004-2.5) to set ISET yields <1% gain variation from –55°C to 125°C. The LT1228CN8 datasheet provides exact resistor equations (R4, R6) for Thevenin-equivalent compensation when a regulated negative supply is available - ensuring gm remains flat across industrial temperature ranges.
Why does LT1228CN8 specify different bandwidth values for the transconductance and current feedback sections?
LT1228CN8 specifies separate bandwidths because its two internal amplifiers have fundamentally different architectures and signal paths: the transconductance stage (Pins 1,2,3,5) has 75MHz bandwidth dependent on ISET current and output load capacitance, while the current feedback amplifier (Pins 1,6,8) achieves 100MHz bandwidth determined by feedback resistor value, supply voltage, and load. These are measured independently - e.g., gm-stage BW drops to ~25MHz with 1kΩ load due to 6pF output capacitance, whereas CFA BW remains 100MHz under identical conditions.
LT1228CN8 Specifications
- Product attributes
- Attribute value
- Manufacturer:
- Analog Devices Inc.
- Series:
- -
- Package/Case:
- 8-DIP (0.300", 7.62mm)
- Packaging:
- Tube
- Product Status:
- Obsolete
- Amplifier Type:
- Current Feedback
- Number of Circuits:
- 1
- Output Type:
- -
- Slew Rate:
- 3500V/µs
- Gain Bandwidth Product:
- -
- -3db Bandwidth:
- 100 MHz
- Current - Input Bias:
- 10 µA
- Voltage - Input Offset:
- 3 mV
- Current - Supply:
- 6mA
- Current - Output / Channel:
- 125 mA
- Voltage - Supply Span (Min):
- 4 V
- Voltage - Supply Span (Max):
- 36 V
- Operating Temperature:
- 0°C ~ 70°C
- Grade:
- -
- Qualification:
- -
- Mounting Type:
- Through Hole
- Supplier Device Package:
- 8-PDIP
LT1228CN8 FAQ
1.How can I place an order for LT1228CN8 through Aetrix?
Please submit a Request for Quotation (RFQ) for LT1228CN8 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 LT1228CN8 reliable?
The price and inventory of LT1228CN8 are updated periodically and may fluctuate due to market conditions. Stock and pricing data are typically refreshed every 24 hours. Quotation validity for LT1228CN8 is usually 5 days.
3.What payment methods are accepted for LT1228CN8?
We accept Wire Transfer, PayPal, Credit Card, Western Union, MoneyGram, and Escrow for LT1228CN8 transactions.
Note: Certain payment methods may incur a processing fee.
4.How is shipping managed for LT1228CN8?
LT1228CN8 orders can be shipped via leading logistics carriers, including DHL, UPS, FedEx, TNT, or Registered Mail.
Once your LT1228CN8 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 LT1228CN8?
For technical support, including LT1228CN8 datasheets, pinout diagrams, or application guidance, please contact our engineering support team. They can provide detailed documentation and assistance for your LT1228CN8 requirements.
6.How does Aetrix verify that LT1228CN8 is sourced from the original manufacturer or authorized distributors?
All LT1228CN8 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 LT1228CN8 meets industry standards.
7.What is the process for return or replacement of LT1228CN8?
All LT1228CN8 units undergo pre-shipment inspection (PSI). If there is an issue with LT1228CN8, 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 LT1228CN8 part is unused and in its original packaging.
Return procedure for LT1228CN8:
1.Submit a request within 90 days.
2.Obtain a Return Material Authorization (RMA) from Aetrix.
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