NMP8A Trimmer Capacitor Equivalent & Substitute Parts

Part Overview

The NMP8A is a 0.8–7pF trimmer capacitor rated for 500V operation, manufactured by Knowles Voltronics. This component features a sapphire dielectric with non-magnetic construction and is designed for user-defined mounting applications. The part is currently classified as obsolete, making identification of suitable substitutes necessary for ongoing design support and component procurement.

Substiute Parts

NMP8A

Knowles VoltronicsIn Stock: 976NMP8A Datasheet

Current PartRFQ

27290NM

Knowles Johanson ManufacturingIn Stock: 99527290NM Datasheet

MFR RecommendedRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitution of the NMP8A is based on the following critical parameters:

• Capacitance Range Overlap: The substitute must cover or exceed the 0.8–7pF range of the original part
• Voltage Rating: Minimum 500V rated voltage is required
• Dielectric Material: Sapphire dielectric ensures equivalent electrical performance and stability
• Physical Dimensions: Compatible size and height allow for mechanical fit in existing designs
• Operating Temperature Range: Must support the –55°C to 125°C operating window
• Moisture Sensitivity: MSL 1 classification ensures no moisture-related constraints

The 27290NM from Knowles Johanson Manufacturing meets these substitution criteria. It extends the capacitance range to 0.8–8pF, maintains 500V rating, uses sapphire dielectric, and operates across the required temperature range. The primary difference is the transition from user-defined mounting to surface mount (SMD) configuration.

Parameter Comparison

Engineering Selection Recommendations

The 27290NM is the manufacturer-recommended substitute for the obsolete NMP8A. Both components share identical voltage rating, dielectric material, and moisture sensitivity classification. The 27290NM provides active product status with RoHS compliance, ensuring long-term availability and regulatory alignment.

The primary design consideration is the mounting transition from user-defined to surface mount configuration. The 27290NM's slightly reduced maximum height (0.480" vs. 0.495") and extended lower operating temperature limit (–65°C vs. –55°C) provide additional design margin. The capacitance range extension to 8pF accommodates applications requiring maximum adjustment range.

Frequently Asked Questions (FAQ)

Q: Can the 27290NM directly replace the NMP8A in existing designs?

A: Electrical substitution is valid based on matching voltage rating, dielectric material, and capacitance range overlap. Mechanical compatibility depends on the original mounting configuration. The transition from user-defined to surface mount requires PCB layout and assembly process evaluation.

Q: What is the significance of the Q factor difference between the two parts?

A: The NMP8A specifies Q of 1500 @ 250MHz, while the 27290NM specifies Q of 3000 @ 100MHz. These measurements are taken at different frequencies and represent the quality factor at those specific operating points. Both values are acceptable for trimmer capacitor applications; the difference reflects measurement methodology rather than inferior performance.

Q: Does the extended capacitance range of the 27290NM (0.8–8pF vs. 0.8–7pF) affect compatibility?

A: No. The extended range is a superset of the original specification. Applications requiring adjustment within the 0.8–7pF window operate identically on the 27290NM.

Q: Is RoHS compliance a requirement for substitution?

A: RoHS compliance of the 27290NM provides regulatory advantage for new designs and procurement. Existing designs using the NMP8A may not require RoHS-compliant substitutes unless mandated by application or regional requirements.

Q: What mounting considerations apply to the 27290NM?

A: The 27290NM is specified as a surface mount device with top adjustment. Original designs using user-defined mounting must be re-evaluated for PCB footprint, solder reflow compatibility, and assembly process requirements.