Dual, High Output Current, High Speed Op Amp# Technical Documentation: LMH6672MRX High-Speed Operational Amplifier
Manufacturer : Texas Instruments (NS - National Semiconductor legacy product)
## 1. Application Scenarios
### Typical Use Cases
The LMH6672MRX is a dual, high-speed, current-feedback operational amplifier designed for applications requiring wide bandwidth, high slew rate, and low distortion. Key use cases include:
- Video Distribution Amplifiers : The device's 400 MHz bandwidth (-3 dB) and 0.1 dB gain flatness to 70 MHz make it ideal for driving multiple video loads while maintaining signal integrity.
- Professional Broadcast Equipment : Used in RGB matrix switchers, video routers, and broadcast distribution systems where multiple high-quality video signals must be routed without degradation.
- Medical Imaging Systems : Suitable for ultrasound front-ends and other imaging equipment requiring high-fidelity signal amplification with minimal harmonic distortion.
- Test and Measurement Equipment : Employed in high-speed signal generators, oscilloscope front-ends, and spectrum analyzer input stages.
- Communications Infrastructure : Base station receivers and transmitters benefit from the amplifier's ability to handle high-frequency analog signals with low noise.
### Industry Applications
- Broadcast & Professional Video : HD-SDI/3G-SDI distribution, video production switchers, camera control units
- Medical Electronics : Ultrasound beamformers, patient monitoring systems, diagnostic imaging
- Industrial Imaging : Machine vision systems, automated inspection equipment
- Military/Aerospace : Radar signal processing, avionics display systems
- Telecommunications : RF signal conditioning, fiber optic transceiver circuits
### Practical Advantages and Limitations
Advantages:
- High Speed : 400 MHz bandwidth and 2100 V/µs slew rate enable excellent high-frequency performance
- Low Distortion : -78 dBc HD2 and -84 dBc HD3 at 10 MHz (RL=150Ω, VO=2Vpp) ensure signal fidelity
- Flexible Power Supply : Operates from ±5V to ±15V supplies, accommodating various system requirements
- Robust Output Drive : Capable of driving up to 100 mA output current, suitable for driving cables and multiple loads
- Thermal Protection : Built-in thermal shutdown prevents damage during fault conditions
Limitations:
- Current-Feedback Architecture : Requires different design approach compared to voltage-feedback op-amps, particularly regarding gain-bandwidth relationship
- Power Consumption : Typically 10.5 mA per amplifier (21 mA total) may be excessive for battery-powered applications
- Limited Rail-to-Rail Performance : Output swings to within approximately 2V of supply rails, which may restrict dynamic range in low-voltage applications
- Sensitivity to Feedback Resistors : Performance optimization requires careful selection of feedback network values
## 2. Design Considerations
### Common Design Pitfalls and Solutions
Pitfall 1: Improper Feedback Resistor Selection
- Issue : Current-feedback amplifiers require specific feedback resistor values for optimal performance. Using incorrect values can cause peaking, oscillation, or reduced bandwidth.
- Solution : Follow manufacturer's recommended RF values (typically 402Ω for LMH6672). Maintain RF/(1 + RF/RG) ≈ 402Ω for different gain configurations.
Pitfall 2: Inadequate Power Supply Decoupling
- Issue : High-speed operation makes the device sensitive to power supply noise and transients.
- Solution : Implement a multi-stage decoupling strategy:
- Place 0.1 µF ceramic capacitors within 5 mm of each supply pin
- Add 10 µF tantalum or electrolytic capacitors at power entry points
- Use separate decoupling for each amplifier in dual configurations
Pitfall 3: Poor Thermal Management
- Issue : The device can dissipate significant
