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LMH6645MA Equivalent & Substitute Parts
Part Overview
The LMH6645MA is a voltage feedback amplifier manufactured by Texas Instruments, featuring a single circuit with push-pull, rail-to-rail output configuration in an 8-SOIC surface mount package. This device is classified as obsolete, which necessitates identification of active equivalent and substitute components for new designs and production continuity. The LMH6645MA delivers a slew rate of 22V/µs with a -3dB bandwidth of 55 MHz, suitable for general-purpose voltage feedback amplification applications requiring moderate speed performance.
Substiute Parts
Key Parameters
| Parameter | Value | Unit |
|---|---|---|
| Amplifier Type | Voltage Feedback | — |
| Number of Circuits | 1 | — |
| Output Type | Push-Pull, Rail-to-Rail | — |
| Slew Rate | 22 | V/µs |
| -3dB Bandwidth | 55 | MHz |
| Current - Input Bias | 650 | nA |
| Voltage - Input Offset | 1 | mV |
| Current - Supply | 725 | µA |
| Current - Output / Channel | 20 | mA |
| Voltage - Supply Span (Min) | 2.5 | V |
| Voltage - Supply Span (Max) | 12 | V |
| Operating Temperature | -40 to 85 | °C |
| Package / Case | 8-SOIC (0.154", 3.90mm Width) | — |
| Mounting Type | Surface Mount | — |
Substitute Part Grouping Explanation
Substitution of the LMH6645MA is determined by strict equivalence in the following electrical and mechanical parameters:
Critical Substitution Criteria:
- Amplifier Type: Voltage Feedback (mandatory)
- Number of Circuits: 1 (mandatory)
- Output Type: Rail-to-Rail configuration (mandatory)
- Package / Case: 8-SOIC form factor (mandatory)
- Mounting Type: Surface Mount (mandatory)
- Operating Temperature Range: Minimum -40°C to maximum 85°C or higher (mandatory)
- Voltage Supply Span: Minimum 2.5V to maximum 12V or wider (mandatory)
Performance Parameters (Secondary Consideration): Substitute parts may exhibit improved or equivalent performance in slew rate, bandwidth, input bias current, and output current capacity, provided they meet all critical criteria above.
The substitute parts identified fall into two categories:
Category 1 - Direct Equivalent (Identical Performance): LMH6645MA/NOPB from National Semiconductor maintains identical electrical specifications and is the direct equivalent variant.
Category 2 - Enhanced Performance Substitutes (Active Status): AD8031 series (Analog Devices) and AD8051/AD8091 series (Analog Devices) provide improved performance characteristics while maintaining full compatibility with the 8-SOIC package and supply voltage requirements. These parts are in active production status with RoHS3 compliance.
Parameter Comparison
| Parameter | LMH6645MA | LMH6645MA/NOPB | AD8031ARZ | AD8031BRZ | AD8051ARZ | AD8091ARZ |
|---|---|---|---|---|---|---|
| Amplifier Type | Voltage Feedback | Voltage Feedback | Voltage Feedback | Voltage Feedback | Voltage Feedback | Voltage Feedback |
| Number of Circuits | 1 | 1 | 1 | 1 | 1 | 1 |
| Output Type | Push-Pull, Rail-to-Rail | Push-Pull, Rail-to-Rail | Rail-to-Rail | Rail-to-Rail | Rail-to-Rail | Rail-to-Rail |
| Slew Rate (V/µs) | 22 | 22 | 35 | 35 | 170 | 170 |
| -3dB Bandwidth (MHz) | 55 | 55 | 80 | 80 | 110 | 110 |
| Current - Input Bias (nA) | 650 | 650 | 450 | 450 | 1400 | 1400 |
| Voltage - Input Offset (mV) | 1 | 1 | 1 | 0.5 | 1.8 | 1.8 |
| Current - Supply (µA) | 725 | 725 | 900 | 900 | 4800 | 4800 |
| Current - Output / Channel (mA) | 20 | 20 | 15 | 15 | 45 | 45 |
| Voltage - Supply Span Min (V) | 2.5 | 2.5 | 2.7 | 2.7 | 3 | 3 |
| Voltage - Supply Span Max (V) | 12 | 12 | 12 | 12 | 12 | 12 |
| Operating Temperature (°C) | -40 to 85 | -40 to 85 | -40 to 85 | -40 to 85 | -40 to 125 | -40 to 85 |
| Package / Case | 8-SOIC | 8-SOIC | 8-SOIC | 8-SOIC | 8-SOIC | 8-SOIC |
| Mounting Type | Surface Mount | Surface Mount | Surface Mount | Surface Mount | Surface Mount | Surface Mount |
| Product Status | Obsolete | Active | Active | Active | Active | Active |
| RoHS Status | Non-compliant | Not specified | ROHS3 Compliant | ROHS3 Compliant | ROHS3 Compliant | ROHS3 Compliant |
Engineering Selection Recommendations
For Direct Replacement (Identical Specifications): The LMH6645MA/NOPB from National Semiconductor is the direct equivalent part. This variant maintains identical electrical performance and package configuration. However, this part should be verified for current availability, as the base LMH6645 series is classified as obsolete.
For New Designs and Production Continuity: The AD8031 series (AD8031ARZ, AD8031ARZ-REEL, AD8031ARZ-REEL7, AD8031BRZ, AD8031BRZ-REEL7) from Analog Devices is recommended as the primary substitute. These parts are in active production status with ROHS3 compliance certification. The AD8031 series provides improved slew rate (35V/µs versus 22V/µs) and bandwidth (80 MHz versus 55 MHz) while maintaining full electrical compatibility within the specified supply voltage range (2.7V to 12V). The AD8031BRZ variants offer superior input offset voltage specification (500 µV versus 1 mV).
For High-Speed Applications: The AD8051 series (AD8051ARZ, AD8051ARZ-REEL, AD8051ARZ-REEL7) and AD8091ARZ provide significantly enhanced performance with slew rate of 170V/µs and bandwidth of 110 MHz. These parts are suitable for applications requiring higher speed performance. Note that AD8051 series supports extended operating temperature to 125°C, while AD8091ARZ maintains the standard -40°C to 85°C range. Supply current increases to 4.8mA and output current capability increases to 45mA.
Compliance Considerations: All recommended Analog Devices substitutes carry ROHS3 compliance certification and REACH unaffected status, suitable for regulated manufacturing environments. The LMH6645MA is RoHS non-compliant and should be replaced in new designs subject to environmental regulations.
Packaging Options: Substitute parts are available in multiple packaging formats: Tube, Cut Tape (CT) & Digi-Reel®, and Tape & Reel (TR). Selection should align with production volume and assembly requirements.
Frequently Asked Questions (FAQ)
Q: Can the AD8031 series directly replace the LMH6645MA in existing designs?
A: Yes, the AD8031 series is electrically compatible for direct substitution. The 8-SOIC package pinout is identical, and the supply voltage range (2.7V to 12V) encompasses the LMH6645MA requirement (2.5V to 12V). The improved slew rate and bandwidth provide enhanced performance without requiring circuit redesign. Verify that the application does not depend on the specific push-pull output characteristic, as AD8031 specifies rail-to-rail output.
Q: What is the difference between AD8031ARZ and AD8031BRZ?
A: Both variants are functionally identical with the same slew rate (35V/µs), bandwidth (80 MHz), and supply current (900µA). The primary difference is input offset voltage specification: AD8031ARZ specifies 1 mV maximum, while AD8031BRZ specifies 500 µV maximum. The "B" grade provides tighter offset voltage tolerance, suitable for precision applications.
Q: Are the different AD8031 packaging variants (REEL, REEL7) electrically equivalent?
A: Yes. The designations REEL and REEL7 refer only to packaging and tape configuration for automated assembly. AD8031ARZ-REEL, AD8031ARZ-REEL7, AD8031BRZ-REEL7 are electrically identical to their base variants. Selection depends on production equipment compatibility and volume requirements.
Q: Why does the AD8051 series have higher supply current (4.8mA) compared to LMH6645MA (725µA)?
A: The AD8051 series is designed for higher-speed applications with slew rate of 170V/µs and bandwidth of 110 MHz, compared to the LMH6645MA at 22V/µs and 55 MHz. The increased supply current reflects the higher performance capability. Use AD8051 only when the application requires this enhanced speed performance.
Q: Is the LMH6645MA/NOPB still available for procurement?
A: The LMH6645MA/NOPB is classified as active status, but the base LMH6645 series is obsolete. Availability should be confirmed with component distributors. For new production, Analog Devices AD8031 or AD8051 series are recommended as they are in active production with confirmed long-term availability.
Q: What is the difference between AD8051ARZ and AD8091ARZ?
A: Both parts have identical electrical specifications: slew rate 170V/µs, bandwidth 110 MHz, input bias current 1.4 µA, and output current 45 mA. The primary difference is operating temperature range: AD8051ARZ supports -40°C to 125°C, while AD8091ARZ supports -40°C to 85°C. Select AD8051 for extended temperature applications.
Q: Can I use the AD8051 series in a design originally specified for LMH6645MA?
A: Yes, the AD8051 series is compatible for direct substitution in the 8-SOIC package. However, verify that the application circuit can accommodate the higher supply current (4.8mA versus 725µA) and higher output current capability (45mA versus 20mA). The improved performance characteristics will not degrade circuit operation in applications designed for the LMH6645MA.
Q: What packaging should I specify for high-volume production?
A: For high-volume automated assembly, specify Cut Tape (CT) & Digi-Reel® packaging variants (AD8031ARZ-REEL7, AD8031BRZ-REEL7, AD8051ARZ-REEL7). These formats are optimized for pick-and-place equipment. For lower volumes or manual assembly, Tube packaging (AD8031ARZ, AD8031BRZ, AD8051ARZ, AD8091ARZ) is appropriate.
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