FDS4780 Equivalent & Substitute Parts

Part Overview

The FDS4780 is an N-Channel MOSFET manufactured by onsemi, rated for 40V drain-to-source voltage with a continuous drain current of 10.8A at 25°C. This device is packaged in an 8-SOIC surface mount configuration and belongs to the PowerTrench® series. The FDS4780 is classified as obsolete, making identification of equivalent and substitute parts necessary for ongoing design support and production continuity. Substitute parts must maintain compatibility across electrical ratings, mechanical packaging, and thermal characteristics to ensure direct replacement capability.

Substiute Parts

FDS4780

onsemiIn Stock: 840FDS4780 Datasheet

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AO4484

Alpha & Omega Semiconductor Inc.In Stock: 12338AO4484 Datasheet

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SI4840BDY-T1-GE3

Vishay SiliconixIn Stock: 1452SI4840BDY-T1-GE3 Datasheet

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Key Parameters

Substitute Part Grouping Explanation

Substitute parts for the FDS4780 are selected based on the following critical parameters that determine functional equivalence:

Electrical Compatibility Criteria:

• Drain-to-Source Voltage (Vdss): Must equal or exceed 40V
• Continuous Drain Current (Id): Must support minimum 10.8A operation
• On-State Resistance (Rds On): Must not exceed 10.5 mOhm at rated current and gate voltage
• Gate Threshold Voltage (Vgs(th)): Must be compatible with 10V drive voltage
• Operating Temperature Range: Must span -55°C to 150°C

Mechanical Compatibility Criteria:

• Package Type: Must be 8-SOIC surface mount configuration
• Pin Configuration: Must maintain identical pinout for direct PCB replacement

Thermal Compatibility Criteria:

• Power Dissipation: Must support minimum 2.5W thermal rating

The substitute parts identified below meet these criteria within the specified tolerances and packaging requirements.

Parameter Comparison

Engineering Selection Recommendations

AO4484 (Alpha & Omega Semiconductor Inc.)

The AO4484 is an active product with ROHS3 compliance. This device matches the FDS4780 in Vdss (40V) and package configuration (8-SOIC). The continuous drain current rating of 10A is marginally lower than the FDS4780 specification of 10.8A. The on-state resistance of 10 mOhm at 10A, 10V is within acceptable tolerance of the FDS4780 specification. The gate threshold voltage is lower (3V versus 5V), which may require circuit evaluation for gate drive compatibility. Power dissipation is rated at 1.7W (Ta), which is lower than the FDS4780 specification of 2.5W (Ta). This part is suitable for applications where the 10A current rating is sufficient and thermal dissipation requirements do not exceed 1.7W.

SI4840BDY-T1-GE3 (Vishay Siliconix)

The SI4840BDY-T1-GE3 is an active product with ROHS3 compliance and belongs to the TrenchFET® series. This device exceeds FDS4780 specifications in continuous drain current (19A at Tc versus 10.8A at Ta) and provides superior on-state resistance performance (9 mOhm at 12.4A, 10V). The package configuration matches the FDS4780 (8-SOIC). Power dissipation is rated at 2.5W (Ta) and 6W (Tc), meeting or exceeding the FDS4780 specification. The gate threshold voltage is lower (3V versus 5V), requiring circuit evaluation for gate drive compatibility. This part is suitable for applications requiring higher current capacity and improved thermal performance.

Frequently Asked Questions (FAQ)

Q: Can the AO4484 directly replace the FDS4780 in all applications?

A: The AO4484 provides electrical compatibility in voltage rating and package type. However, the continuous drain current specification of 10A is lower than the FDS4780 specification of 10.8A. Applications operating at or near 10.8A continuous current require verification that 10A operation is acceptable. The lower gate threshold voltage (3V versus 5V) requires evaluation of gate drive circuit compatibility.

Q: What are the advantages of the SI4840BDY-T1-GE3 over the FDS4780?

A: The SI4840BDY-T1-GE3 provides higher continuous drain current (19A), lower on-state resistance (9 mOhm), and enhanced thermal performance (6W at Tc). These characteristics result in reduced power dissipation and improved thermal efficiency in high-current applications. The device maintains identical package configuration and voltage rating.

Q: Are there thermal considerations when substituting these parts?

A: Yes. The FDS4780 is rated for 2.5W (Ta) power dissipation. The AO4484 is rated for 1.7W (Ta), which is lower and may require thermal management evaluation in applications approaching maximum power dissipation. The SI4840BDY-T1-GE3 is rated for 2.5W (Ta) and 6W (Tc), providing superior thermal headroom.

Q: Do the substitute parts have identical pinouts?

A: All substitute parts are packaged in 8-SOIC configuration with identical mechanical dimensions (0.154", 3.90mm Width). Direct PCB replacement is supported without layout modifications.

Q: What is the impact of different gate threshold voltages?

A: The FDS4780 has a gate threshold voltage of 5V, while both substitute parts specify 3V. This difference affects gate drive circuit design. Lower threshold voltage allows operation with lower gate drive voltages but may require circuit verification to ensure proper switching characteristics and noise immunity in the target application.

Q: Are the substitute parts RoHS compliant?

A: The AO4484 and SI4840BDY-T1-GE3 are both ROHS3 compliant. The FDS4780 status is not specified in the provided data. Both active substitutes meet current environmental compliance requirements.

Q: What is the difference between Ta and Tc temperature ratings?

A: Ta refers to ambient temperature, while Tc refers to case temperature. The SI4840BDY-T1-GE3 provides power dissipation specifications for both conditions (2.5W at Ta, 6W at Tc), allowing more accurate thermal calculations based on actual mounting and cooling conditions.