FDS4770 Equivalent & Substitute Parts

Part Overview

The FDS4770 is an N-Channel MOSFET manufactured by onsemi, rated for 40V drain-to-source voltage with 13.2A continuous drain current at 25°C. The device is housed in an 8-SOIC surface mount package and features a maximum on-resistance of 7.5mOhm at 13.2A and 10V gate-source voltage. The FDS4770 is classified as obsolete, making identification of equivalent substitute components necessary for ongoing design support and procurement continuity. Substitute parts must maintain compatibility across voltage ratings, current handling, package configuration, and thermal characteristics to ensure functional equivalence in existing circuit applications.

Key Parameters

Parameter	Value	Unit
Drain-to-Source Voltage (Vdss)	40	V
Continuous Drain Current (Id) @ 25°C	13.2	A (Ta)
On-Resistance (Rds On Max) @ 13.2A, 10V	7.5	mOhm
Gate-Source Threshold Voltage (Vgs(th)) @ 250µA	5	V
Gate Charge (Qg) @ 10V	67	nC
Power Dissipation (Max)	2.5	W (Ta)
Operating Temperature Range	-55 to 150	°C (TJ)
Package Type	8-SOIC	Surface Mount
Package Dimensions	0.154" × 3.90mm Width	8-SOIC

Substitute Part Grouping Explanation

Substitute parts for the FDS4770 are qualified based on the following electrical and mechanical parameters:

Critical Matching Parameters:

Drain-to-Source Voltage (Vdss): 40V minimum
Package Type: 8-SOIC surface mount configuration
Mounting Type: Surface mount with identical footprint dimensions (0.154" × 3.90mm Width)
FET Type: N-Channel MOSFET technology
Operating Temperature Range: Minimum -55°C to 150°C overlap

Performance Parameters for Functional Equivalence:

Continuous Drain Current (Id): Equal to or greater than 13.2A at 25°C
On-Resistance (Rds On): Equal to or less than 7.5mOhm at rated current and 10V gate-source voltage
Gate-Source Threshold Voltage (Vgs(th)): 5V maximum at 250µA
Power Dissipation: 2.5W (Ta) minimum rating

The FDS4470 and SI4124DY-T1-GE3 meet these substitution criteria with compatible electrical specifications and identical package configurations.

Parameter Comparison

Parameter	FDS4770 (Main)	FDS4470 (Substitute)	SI4124DY-T1-GE3 (Substitute)	Unit
Manufacturer	onsemi	Fairchild Semiconductor	Vishay Siliconix	—
Product Status	Obsolete	Active	Active	—
Drain-to-Source Voltage (Vdss)	40	40	40	V
Continuous Drain Current (Id) @ 25°C	13.2	12.5	20.5	A (Ta/Tc)
On-Resistance (Rds On Max) @ Rated Current, 10V	7.5 @ 13.2A	9 @ 12.5A	7.5 @ 14A	mOhm
Gate-Source Threshold Voltage (Vgs(th)) @ 250µA	5	5	3	V
Gate Charge (Qg) @ 10V	67	63	77	nC
Input Capacitance (Ciss) @ 20V	2819	2659	3540	pF
Power Dissipation (Max)	2.5 (Ta)	2.5 (Ta)	2.5 (Ta), 5.7 (Tc)	W
Operating Temperature Range	-55 to 150	-55 to 175	-55 to 150	°C (TJ)
Package Type	8-SOIC	8-SOIC	8-SOIC	Surface Mount
Package Dimensions	0.154" × 3.90mm	0.154" × 3.90mm	0.154" × 3.90mm	Width
FET Type	N-Channel	N-Channel	N-Channel	—
Technology	MOSFET (Metal Oxide)	MOSFET (Metal Oxide)	MOSFET (Metal Oxide)	—
Mounting Type	Surface Mount	Surface Mount	Surface Mount	—

Engineering Selection Recommendations

FDS4470 (Fairchild Semiconductor)

The FDS4470 is an active product with identical voltage rating (40V Vdss) and package configuration (8-SOIC) to the FDS4770. The continuous drain current specification of 12.5A is within 5% of the FDS4770's 13.2A rating, making it suitable for applications where the load current does not exceed 12.5A. The on-resistance of 9mOhm at 12.5A and 10V is slightly higher than the FDS4770's 7.5mOhm, resulting in marginally increased power dissipation in high-current switching scenarios. The FDS4470 supports an extended operating temperature range to 175°C, providing additional thermal margin. This substitute is appropriate for direct replacement in applications with current requirements up to 12.5A.

SI4124DY-T1-GE3 (Vishay Siliconix)

The SI4124DY-T1-GE3 is an active product with identical voltage rating (40V Vdss) and package configuration (8-SOIC) to the FDS4770. The continuous drain current specification of 20.5A at Tc significantly exceeds the FDS4770's 13.2A requirement, providing substantial current margin. The on-resistance of 7.5mOhm at 14A and 10V matches the FDS4770's specification, ensuring equivalent switching performance. The SI4124DY-T1-GE3 features enhanced power dissipation capability (5.7W at Tc) compared to the FDS4770's 2.5W (Ta), enabling operation in higher thermal environments. The lower gate-source threshold voltage (3V versus 5V) may require circuit evaluation for gate drive compatibility. This substitute is appropriate for applications requiring higher current capacity or enhanced thermal performance.

Frequently Asked Questions (FAQ)

Q: Can the FDS4470 be used as a direct replacement for the FDS4770 in all applications?

A: The FDS4470 is suitable for applications where the continuous drain current requirement does not exceed 12.5A. The FDS4770 is rated for 13.2A, so applications operating near or above 12.5A should use the SI4124DY-T1-GE3 instead. Both devices share identical voltage ratings, package configuration, and threshold voltage specifications, enabling direct PCB footprint compatibility.

Q: What are the key differences between the FDS4470 and SI4124DY-T1-GE3 substitutes?

A: The primary differences are continuous drain current (12.5A versus 20.5A), on-resistance measurement conditions (12.5A versus 14A), gate-source threshold voltage (5V versus 3V), and power dissipation capability (2.5W Ta versus 5.7W Tc). Both devices maintain the 40V voltage rating and 8-SOIC package. The SI4124DY-T1-GE3 provides higher current capacity and thermal performance, while the FDS4470 maintains closer electrical alignment to the FDS4770's original specifications.

Q: Are there any gate drive circuit considerations when substituting the SI4124DY-T1-GE3?

A: The SI4124DY-T1-GE3 has a lower gate-source threshold voltage (3V) compared to the FDS4770 (5V). Existing gate drive circuits designed for the FDS4770 will function with the SI4124DY-T1-GE3, but the lower threshold may result in earlier device turn-on. Circuit evaluation is necessary if gate drive timing is critical to application performance.

Q: Do all three devices use the same 8-SOIC package footprint?

A: Yes. The FDS4770, FDS4470, and SI4124DY-T1-GE3 all use the 8-SOIC surface mount package with identical dimensions (0.154" × 3.90mm Width). PCB layout and footprint modifications are not required when substituting between these devices.

Q: What is the impact of the higher on-resistance in the FDS4470 compared to the FDS4770?

A: The FDS4470 has an on-resistance of 9mOhm at 12.5A and 10V, compared to the FDS4770's 7.5mOhm at 13.2A and 10V. This 1.5mOhm difference results in increased power dissipation during conduction. In applications with continuous high current operation, this may require thermal management evaluation. For switching applications with low duty cycles, the impact is typically negligible.

Q: Can the SI4124DY-T1-GE3 be used in applications originally designed for the FDS4770?

A: Yes. The SI4124DY-T1-GE3 meets or exceeds all critical electrical specifications of the FDS4770, including voltage rating, on-resistance, and operating temperature range. The higher current capacity (20.5A versus 13.2A) and enhanced thermal performance (5.7W Tc) make it suitable for direct substitution. Gate drive circuit evaluation is recommended due to the lower threshold voltage (3V versus 5V).

Q: What is the product status significance for component selection?

A: The FDS4770 is classified as obsolete, indicating onsemi has discontinued production and support. The FDS4470 and SI4124DY-T1-GE3 are both active products with ongoing manufacturer support, availability, and technical documentation. Selection of active substitute parts ensures long-term supply chain reliability and access to current technical resources.

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