FDS8984-F085 Equivalent & Substitute Parts

Part Overview

The FDS8984-F085 is a dual N-channel MOSFET array manufactured by onsemi, rated for 30V drain-to-source voltage and 7A continuous drain current in an 8-SOIC surface mount package. This device is classified as obsolete, which necessitates identification of equivalent and substitute components for ongoing design support and production continuity. The part qualifies for automotive applications under AEC-Q101 and complies with RoHS3 standards.

Key Parameters

Parameter	Value	Unit
Drain-to-Source Voltage (Vdss)	30	V
Continuous Drain Current (Id) @ 25°C	7	A
On-Resistance (Rds On) @ 7A, 10V	23	mOhm
Gate Threshold Voltage (Vgs(th)) @ 250µA	2.5	V
Gate Charge (Qg) @ 10V	13	nC
Input Capacitance (Ciss) @ 15V	635	pF
Maximum Power Dissipation	1.6	W
Operating Temperature Range	-55 to 150	°C
Configuration	2 N-Channel (Dual)	—
Package	8-SOIC (0.154", 3.90mm Width)	—
FET Feature	Logic Level Gate	—

Substitute Part Grouping Explanation

Substitution of the FDS8984-F085 is determined by the following critical parameters:

Electrical Compatibility Requirements:

Drain-to-source voltage (Vdss) must be greater than or equal to 30V
Continuous drain current (Id) must be greater than or equal to 7A
On-resistance (Rds On) must not exceed the original specification to maintain thermal performance
Gate threshold voltage (Vgs(th)) must be compatible with logic-level gate drive circuits
Operating temperature range must encompass -55°C to 150°C

Mechanical Compatibility Requirements:

Package must be 8-SOIC surface mount configuration
Pin pitch and footprint must match 0.154" (3.90mm) width specification
Dual N-channel configuration must be maintained

Compliance Requirements:

RoHS3 compliance is mandatory
Automotive qualification (AEC-Q101) is required for applications in automotive environments
Moisture sensitivity level (MSL) of 1 (Unlimited) is preferred

Substitute parts are grouped into two categories: direct substitutes (meeting or exceeding all electrical parameters within the same package) and functional alternatives (meeting minimum electrical requirements with potential trade-offs in performance characteristics).

Parameter Comparison

Parameter	FDS8984-F085 (Main)	SQ4940AEY-T1_GE3	AO4842	SH8KA4TB	SI4214DDY-T1-GE3	SI4808DY-T1-E3	SP8K3TB	STS10DN3LH5	STS8DN3LLH5
Manufacturer	onsemi	Vishay Siliconix	Alpha & Omega	Rohm	Vishay Siliconix	Vishay Siliconix	Rohm	STMicroelectronics	STMicroelectronics
Vdss (V)	30	40	30	30	30	30	30	30	30
Id @ 25°C (A)	7	8	—	9	8.5	5.7	7	10	10
Rds On @ 10V (mOhm)	23 @ 7A	24 @ 5.3A	22 @ 7.5A	21.4 @ 9A	19.5 @ 8A	22 @ 7.5A	24 @ 7A	21 @ 5A	19 @ 5A
Vgs(th) @ 250µA (V)	2.5	2.5	2.6	2.5 @ 1mA	2.5	0.8 (Min)	2.5 @ 1mA	1.0	1.0
Qg @ 10V (nC)	13	43	11	15.5	22	20	11.8 @ 5V	4.6 @ 5V	5.4 @ 4.5V
Ciss @ 15V (pF)	635	741 @ 20V	448	640	660	—	600 @ 10V	475 @ 25V	724 @ 25V
Power Max (W)	1.6	4	2	3	3.1	1.1	2	2.5	2.7
Operating Temp (°C)	-55 to 150	-55 to 175	-55 to 150	-55 to 150	-55 to 150	-55 to 150	150 (Max)	-55 to 150	-55 to 150
Configuration	2 N-Channel	2 N-Channel	2 N-Channel	2 N-Channel	2 N-Channel	2 N-Channel	2 N-Channel	2 N-Channel	2 N-Channel
Package	8-SOIC	8-SOIC	8-SOIC	8-SOP	8-SOIC	8-SOIC	8-SOP	8-SOIC	8-SOIC
Product Status	Obsolete	Active	Not For New Designs	Not For New Designs	Active	Active	Active	Not For New Designs	Active
AEC-Q101	Yes	Yes	—	—	—	—	—	—	—
RoHS3	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes	Yes

Engineering Selection Recommendations

Primary Substitute: STS8DN3LLH5 (STMicroelectronics)

The STS8DN3LLH5 is the recommended primary substitute for the FDS8984-F085. This part maintains the 30V Vdss rating and 8-SOIC package configuration. It exceeds the minimum 7A continuous drain current requirement with a 10A rating and demonstrates superior on-resistance performance (19 mOhm at 5A, 10V). The device is currently in active production status, ensuring long-term availability. RoHS3 compliance and MSL 1 rating are confirmed. The lower gate charge (5.4 nC) and reduced input capacitance (724 pF) provide improved switching characteristics compared to the original part.

Secondary Substitute: SI4214DDY-T1-GE3 (Vishay Siliconix)

The SI4214DDY-T1-GE3 offers a 30V/8.5A configuration in the 8-SOIC package with active product status. This part delivers improved on-resistance (19.5 mOhm at 8A, 10V) and higher power dissipation capability (3.1W). The TrenchFET® series technology provides enhanced performance characteristics. RoHS3 compliance is confirmed. This substitute is suitable for applications requiring higher current capacity within the same voltage class.

Tertiary Substitute: SQ4940AEY-T1_GE3 (Vishay Siliconix)

The SQ4940AEY-T1_GE3 provides a 40V/8A configuration, offering increased voltage headroom for applications with higher transient voltage requirements. The 8-SOIC package maintains mechanical compatibility. Active product status and AEC-Q101 qualification ensure automotive-grade reliability. The higher Vdss rating (40V) allows operation in circuits with greater voltage margins. RoHS3 compliance is confirmed.

Alternative Substitute: SP8K3TB (Rohm Semiconductor)

The SP8K3TB matches the 30V/7A electrical specification and maintains the 8-SOP package footprint. Active product status supports long-term availability. RoHS3 compliance is confirmed. This part is suitable for direct replacement in applications where the exact current and voltage ratings are critical. Note that operating temperature specification is limited to 150°C maximum (not -55°C to 150°C range).

Not Recommended for New Designs:

AO4842 and SH8KA4TB are classified as "Not For New Designs" and should be avoided for new product development. STS10DN3LH5 is also classified as "Not For New Designs" despite its superior electrical characteristics. These parts may be used only for legacy system maintenance or repair applications where exact compatibility is required.

Frequently Asked Questions (FAQ)

Q: Can the FDS8984-F085 be directly replaced with any of these substitutes without circuit modification?

A: Direct replacement is possible with STS8DN3LLH5, SI4214DDY-T1-GE3, and SP8K3TB, provided the 8-SOIC package footprint is used. These parts maintain the 30V Vdss rating and dual N-channel configuration. However, SP8K3TB uses an 8-SOP package variant, which may require PCB layout verification. SQ4940AEY-T1_GE3 operates at 40V and requires circuit validation to confirm compatibility with existing voltage ratings.

Q: What is the significance of the "Not For New Designs" status?

A: Parts designated as "Not For New Designs" are in end-of-life phases and may have limited availability or production support. These parts should only be used for maintaining existing products or repairing legacy systems. For new product development, select parts with "Active" product status: STS8DN3LLH5, SI4214DDY-T1-GE3, SQ4940AEY-T1_GE3, or SP8K3TB.

Q: How do on-resistance differences affect circuit performance?

A: On-resistance (Rds On) directly impacts power dissipation and thermal performance. Lower Rds On values reduce heat generation at the same current levels. STS8DN3LLH5 (19 mOhm) and SI4214DDY-T1-GE3 (19.5 mOhm) provide superior thermal performance compared to the original FDS8984-F085 (23 mOhm). In high-current applications, this difference can reduce junction temperature by several degrees Celsius.

Q: Are there package compatibility concerns between 8-SOIC and 8-SOP variants?

A: 8-SOIC and 8-SOP packages have different physical dimensions and pin spacing. While both are 8-pin surface mount packages with 0.154" (3.90mm) width, the SOP variant may have different lead lengths and body profiles. PCB footprint verification is required before substituting SH8KA4TB or SP8K3TB (8-SOP) for the original 8-SOIC package. Consult package datasheets for precise dimensional specifications.

Q: What is the importance of gate threshold voltage (Vgs(th)) in substitution?

A: Gate threshold voltage determines the gate-source voltage required to turn the MOSFET on. The original FDS8984-F085 specifies 2.5V at 250µA. Most substitutes maintain this specification (SQ4940AEY-T1_GE3, SH8KA4TB, SI4214DDY-T1-GE3, SP8K3TB). However, STS10DN3LH5 and STS8DN3LLH5 specify 1.0V, which indicates enhanced gate sensitivity. This lower threshold may require gate drive circuit validation in applications with marginal drive voltage.

Q: How does gate charge (Qg) affect switching performance?

A: Gate charge represents the total charge required to switch the MOSFET from off to on state. Lower gate charge reduces switching losses and allows faster switching speeds. The original part specifies 13 nC at 10V. Substitutes with lower gate charge (STS10DN3LH5 at 4.6 nC, STS8DN3LLH5 at 5.4 nC, AO4842 at 11 nC) provide improved switching efficiency. Higher gate charge values (SQ4940AEY-T1_GE3 at 43 nC) may increase switching losses in high-frequency applications.

Q: Is AEC-Q101 qualification required for all applications?

A: AEC-Q101 qualification is mandatory for automotive applications. The original FDS8984-F085 carries this qualification. Among the substitutes, only SQ4940AEY-T1_GE3 explicitly confirms AEC-Q101 qualification. For non-automotive applications, AEC-Q101 qualification is not required, allowing use of other substitutes. For automotive designs, SQ4940AEY-T1_GE3 is the only substitute with confirmed automotive qualification.

Q: What does RoHS3 compliance mean for component selection?

A: RoHS3 (Restriction of Hazardous Substances Directive 3) compliance indicates that the component does not contain restricted substances such as lead, cadmium, or mercury. All listed substitutes are RoHS3 compliant, matching the original part's environmental compliance status. This compliance is mandatory for products sold in the European Union and increasingly required in other markets.

Q: Can the FDS8984-F085 be used in new designs, or must a substitute be selected?

A: The FDS8984-F085 is classified as obsolete and should not be used in new designs. Obsolete parts have no guaranteed future availability and may be subject to supply discontinuation. For new product development, select an active substitute such as STS8DN3LLH5, SI4214DDY-T1-GE3, or SQ4940AEY-T1_GE3 to ensure long-term production support and component availability.

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