FSQ321LX Equivalent & Substitute Parts

Part Overview

The FSQ321LX is an offline switch flyback converter IC manufactured by onsemi, designed for isolated power management applications. This 8-LSOP surface mount device operates in the 55kHz to 67kHz switching frequency range with 12W power handling capability. The part is classified as obsolete, making equivalent and substitute parts necessary for new designs and ongoing production support. Substitute parts must maintain compatibility with the isolated flyback topology, voltage specifications, and thermal operating range while accommodating modern component availability.

Substiute Parts

FSQ321LX

onsemiIn Stock: 2145FSQ321LX Datasheet

Current PartRFQ

NCP1075AAP100G

onsemiIn Stock: 908NCP1075AAP100G Datasheet

MFR RecommendedRFQ

FSQ0265RLX

onsemiIn Stock: 24889FSQ0265RLX Datasheet

Parametric EquivalentRFQ

FSQ0365RLX

onsemiIn Stock: 1433FSQ0365RLX Datasheet

Parametric EquivalentRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitution for the FSQ321LX is determined by the following critical parameters: isolated flyback topology, 650V breakdown voltage, 8V to 20V supply voltage range, 55kHz to 67kHz switching frequency, and surface mount 8-LSOP packaging. Substitute parts must maintain these core electrical and mechanical specifications to ensure drop-in compatibility within existing circuit designs.

The substitute parts are grouped into two categories:

Parametric Equivalents (Same Package, Same Topology): FSQ0265RLX and FSQ0365RLX maintain identical package form factor (8-LSOP), switching frequency range (55kHz ~ 67kHz), voltage specifications, and fault protection features. These parts differ primarily in power rating (20W and 25W respectively) and product status, with FSQ0365RLX classified as active.

Manufacturer Recommended Substitute (Different Package, Enhanced Specifications): NCP1075AAP100G represents an active alternative with higher switching frequency (100kHz), improved thermal range (-40°C ~ 125°C), and enhanced fault protection including short circuit detection. This part requires through-hole mounting (7-PDIP package) rather than surface mount, necessitating PCB redesign.

Parameter Comparison

Engineering Selection Recommendations

For new designs and production requiring surface mount technology with minimal PCB redesign, FSQ0365RLX is the preferred substitute. This part maintains identical package geometry (8-LSOP), electrical specifications (650V breakdown, 8V-20V supply, 55kHz-67kHz switching), and thermal operating range as the FSQ321LX while offering active product status and higher power capacity (25W). FSQ0365RLX is ROHS3 compliant and currently in stock.

FSQ0265RLX provides an intermediate option with 20W power handling and identical package specifications, though it carries obsolete product status similar to the original FSQ321LX.

NCP1075AAP100G serves as an alternative for applications where through-hole mounting is acceptable and higher switching frequency (100kHz) provides design advantages. This part offers extended operating temperature range (-40°C to 125°C), enhanced fault protection including short circuit detection, and active product status. Implementation requires PCB redesign to accommodate 7-PDIP through-hole package format.

All substitute parts maintain ROHS3 compliance and are manufactured by onsemi, ensuring regulatory consistency and supply chain continuity.

Frequently Asked Questions (FAQ)

Q: Can FSQ0265RLX or FSQ0365RLX be used as direct replacements for FSQ321LX without PCB modification?

A: Yes. Both FSQ0265RLX and FSQ0365RLX use identical 8-LSOP surface mount packaging with matching pinout and electrical specifications (650V breakdown, 8V-20V supply range, 55kHz-67kHz switching frequency). No PCB layout changes are required for these substitutions.

Q: What is the primary difference between FSQ0265RLX and FSQ0365RLX?

A: The primary difference is power rating: FSQ0265RLX handles 20W while FSQ0365RLX handles 25W. Both maintain identical switching frequency, voltage specifications, and package format. FSQ0365RLX carries active product status, whereas FSQ0265RLX is obsolete.

Q: Why does NCP1075AAP100G require PCB redesign?

A: NCP1075AAP100G uses a 7-PDIP through-hole package instead of the 8-LSOP surface mount package. This requires different PCB footprint, via placement, and assembly process. Additionally, the switching frequency is 100kHz rather than 55kHz-67kHz, which may affect transformer and filter component selection.

Q: Are all substitute parts ROHS3 compliant?

A: Yes. FSQ321LX, FSQ0265RLX, FSQ0365RLX, and NCP1075AAP100G are all ROHS3 compliant, meeting regulatory requirements for hazardous substance restrictions.

Q: Which substitute part is recommended for new production?

A: FSQ0365RLX is recommended for new production designs requiring surface mount technology. It maintains full compatibility with FSQ321LX designs while offering active product status, higher power capacity (25W), and assured long-term availability.

Q: What is the startup voltage difference between FSQ321LX and NCP1075AAP100G?

A: FSQ321LX requires 12V startup voltage, while NCP1075AAP100G requires 8.4V. This lower startup requirement in NCP1075AAP100G may provide advantages in low-input-voltage applications but requires circuit validation.