FDS7788 N-Channel MOSFET 30V 18A Equivalent & Substitute Parts

Part Overview

The FDS7788 is an N-Channel MOSFET manufactured by onsemi, rated for 30V drain-to-source voltage with 18A continuous drain current at 25°C. This device is packaged in an 8-SOIC surface mount configuration and is part of the PowerTrench® series. The FDS7788 is classified as obsolete, making identification of equivalent and substitute parts necessary for ongoing design support, production continuity, and component sourcing.

Key Parameters

Parameter	Value	Unit
FET Type	N-Channel	—
Drain to Source Voltage (Vdss)	30	V
Continuous Drain Current (Id) @ 25°C	18	A
Rds On (Max) @ 18A, 10V	4	mOhm
Power Dissipation (Max)	2.5	W
Operating Temperature Range	-55 to 150	°C
Package Type	8-SOIC	—
Mounting Type	Surface Mount	—

Substitute Part Grouping Explanation

Substitution of the FDS7788 is determined by strict equivalence across the following critical parameters:

Primary Substitution Criteria:

Drain-to-Source Voltage (Vdss): 30V minimum
Continuous Drain Current (Id): 18A or greater at 25°C
Package Type: 8-SOIC or 8-SO (mechanically compatible)
Mounting Type: Surface Mount
Operating Temperature Range: -55°C to 150°C minimum
FET Technology: N-Channel MOSFET (Metal Oxide)

Secondary Compatibility Parameters:

Rds On (Max): 5.5 mOhm or lower at rated conditions
Power Dissipation: 2.5W or greater
Gate Voltage (Vgs Max): ±20V
Moisture Sensitivity Level: 1 (Unlimited)

Substitute parts must meet or exceed the primary criteria. Variations in gate charge, input capacitance, and threshold voltage are acceptable provided the device maintains functional equivalence within the specified electrical envelope.

Parameter Comparison

Parameter	FDS7788	FDS8870	AO4430	IRF7832TRPBF	IRF8736TRPBF	SI4430BDY-T1-GE3
Manufacturer	onsemi	onsemi	Alpha & Omega Semiconductor	Infineon Technologies	Infineon Technologies	Vishay Siliconix
FET Type	N-Channel	N-Channel	N-Channel	N-Channel	N-Channel	N-Channel
Vdss (V)	30	30	30	30	30	30
Id @ 25°C (A)	18	18	18	20	18	14
Rds On (Max) @ 10V (mOhm)	4	4.2	5.5	4	4.8	4.5
Power Dissipation (Max) (W)	2.5	2.5	3	2.5	2.5	1.6
Operating Temperature (°C)	-55 to 150	-55 to 150	-55 to 150	-55 to 155	-55 to 150	-55 to 150
Package	8-SOIC	8-SOIC	8-SOIC	8-SO	8-SO	8-SOIC
Product Status	Obsolete	Active	Not For New Designs	Active	Active	Active
RoHS Status	—	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant

Engineering Selection Recommendations

Primary Recommendation: FDS8870

The FDS8870 is the direct successor to the FDS7788 within the onsemi product line. Both devices share identical voltage and current ratings (30V, 18A), matching package geometry (8-SOIC), and equivalent power dissipation (2.5W). The FDS8870 carries Active product status and ROHS3 compliance, ensuring long-term availability and regulatory alignment. Rds On performance is nearly identical (4.2 mOhm versus 4 mOhm), with negligible impact on thermal performance. This part is the preferred choice for direct replacement in existing designs.

Secondary Recommendation: IRF8736TRPBF

The IRF8736TRPBF from Infineon Technologies meets all primary substitution criteria with Active product status and ROHS3 compliance. It maintains 30V/18A ratings with 4.8 mOhm Rds On and 2.5W power dissipation. The 8-SO package is mechanically compatible with 8-SOIC footprints. Gate charge is lower (26 nC versus 48 nC), resulting in faster switching characteristics. This device is suitable for applications where improved switching performance is beneficial.

Tertiary Recommendation: IRF7832TRPBF

The IRF7832TRPBF provides enhanced current capability (20A versus 18A) at identical voltage ratings and power dissipation. This device offers design margin for applications approaching current limits. Rds On is 4 mOhm, matching the FDS7788 specification. Operating temperature extends to 155°C, providing additional thermal headroom. ROHS3 compliance and Active status ensure regulatory and supply chain continuity.

Not Recommended: AO4430

While the AO4430 meets voltage and current specifications, it carries a "Not For New Designs" product status. This classification indicates the manufacturer is discontinuing support. Additionally, higher Rds On (5.5 mOhm) and input capacitance (7270 pF) result in increased power dissipation and switching losses compared to the FDS7788.

Not Recommended: SI4430BDY-T1-GE3

The SI4430BDY-T1-GE3 has reduced continuous drain current (14A versus 18A) and lower power dissipation rating (1.6W versus 2.5W). This device does not meet the current requirement and is unsuitable for direct substitution in applications designed for 18A operation.

Frequently Asked Questions (FAQ)

Q: Can the FDS8870 be used as a direct replacement for the FDS7788?

A: Yes. The FDS8870 is electrically and mechanically equivalent to the FDS7788. Both devices are rated for 30V/18A operation in 8-SOIC packages with 2.5W power dissipation. The FDS8870 is the active production equivalent and is the recommended replacement.

Q: What is the difference between 8-SOIC and 8-SO packages?

A: 8-SOIC and 8-SO refer to the same physical package outline with identical pin spacing and footprint dimensions (0.154" width, 3.90mm). These designations are manufacturer-specific nomenclature. Devices in either package are mechanically interchangeable on standard PCB layouts.

Q: Why does the IRF8736TRPBF have lower gate charge than the FDS7788?

A: Gate charge (Qg) is a device-specific parameter determined by internal capacitance and switching characteristics. Lower gate charge in the IRF8736TRPBF (26 nC versus 48 nC) results in faster switching transitions and reduced gate drive power requirements. This is a performance advantage with no compatibility impact.

Q: Is the AO4430 suitable for new designs?

A: No. The AO4430 carries a "Not For New Designs" status, indicating the manufacturer is phasing out this device. New designs should use FDS8870, IRF8736TRPBF, or IRF7832TRPBF to ensure long-term component availability and manufacturer support.

Q: Can I use the IRF7832TRPBF in place of the FDS7788 if my application only requires 18A?

A: Yes. The IRF7832TRPBF is rated for 20A continuous drain current, exceeding the 18A requirement. All other electrical parameters (30V Vdss, 2.5W power dissipation, -55°C to 155°C operating range) are compatible. The higher current rating provides design margin without penalty.

Q: What is the impact of higher Rds On in the AO4430?

A: The AO4430 has 5.5 mOhm Rds On compared to 4 mOhm in the FDS7788. At 18A continuous current, this results in approximately 0.54W additional power dissipation (I²R loss), reducing thermal margin and potentially requiring larger heatsinks or derating. This makes the AO4430 unsuitable for direct replacement.

Q: Are all substitute parts ROHS3 compliant?

A: FDS8870, IRF8736TRPBF, IRF7832TRPBF, AO4430, and SI4430BDY-T1-GE3 are all ROHS3 compliant. The original FDS7788 does not specify RoHS status. All active and recommended substitutes meet current environmental and regulatory requirements.

Q: What is the operating temperature difference between FDS7788 and IRF7832TRPBF?

A: The FDS7788 operates from -55°C to 150°C (TJ), while the IRF7832TRPBF extends to -55°C to 155°C (TJ). The 5°C additional upper temperature rating in the IRF7832TRPBF provides marginal thermal headroom but does not affect compatibility in standard applications.

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