AO3402 N-Channel MOSFET 30V 4A SOT-23-3 Equivalent & Substitute Parts

Part Overview

The AO3402 is an N-Channel metal oxide semiconductor field-effect transistor (MOSFET) manufactured by Alpha & Omega Semiconductor Inc., rated for 30V drain-to-source voltage and 4A continuous drain current in a surface mount SOT-23-3 package. This device is classified as "Not For New Designs," indicating it has been superseded in the manufacturer's product line. Identifying equivalent and substitute parts is necessary for ongoing production support, maintenance applications, and design continuity where the AO3402 remains specified.

Key Parameters

Parameter	Value	Unit
FET Type	N-Channel	—
Drain-to-Source Voltage (Vdss)	30	V
Continuous Drain Current (Id) @ 25°C	4	A
On-Resistance (Rds On) @ 4A, 10V	55	mOhm
Gate Threshold Voltage (Vgs(th)) @ 250µA	1.4	V
Gate Charge (Qg) @ 4.5V	4.34	nC
Input Capacitance (Ciss) @ 15V	390	pF
Power Dissipation (Max)	1.4	W
Operating Temperature Range	-55 to 150	°C
Package Type	SOT-23-3	—
Mounting Type	Surface Mount	—
RoHS Status	ROHS3 Compliant	—
Moisture Sensitivity Level	1 (Unlimited)	—

Substitute Part Grouping Explanation

Substitution of the AO3402 is determined by strict alignment of electrical and mechanical parameters. The primary substitution criteria are:

Critical Parameters (Must Match or Exceed):

FET Type: N-Channel
Drain-to-Source Voltage (Vdss): 30V minimum
Continuous Drain Current (Id): 4A minimum at 25°C
Package Type: SOT-23-3 surface mount
Operating Temperature Range: -55°C to 150°C minimum

Secondary Parameters (Should Match Closely):

On-Resistance (Rds On): 55 mOhm or lower at rated conditions
Gate Threshold Voltage (Vgs(th)): 1.4V nominal
Power Dissipation: 1.4W or higher
Gate Charge (Qg): Low values preferred for switching speed
Input Capacitance (Ciss): Affects gate drive requirements

Substitute parts are grouped into two categories:

Category A – Direct Functional Equivalents: Parts meeting or exceeding all critical parameters with comparable secondary parameters. These include AOSS32338C, DMG3418L-7, and AO3418.

Category B – Partial Equivalents: Parts with reduced current rating (2.2A to 2.4A) or lower power dissipation but maintaining 30V Vdss and SOT-23-3 packaging. These include FDN337N and NTR4170NT1G. These are suitable only where application current requirements are lower than 4A.

Category C – Voltage-Reduced Alternatives: Parts with 20V Vdss rating. These include IRLML2502TRPBF and NTR4501NT1G. These are suitable only where application voltage does not exceed 20V.

Parts not meeting the 30V/4A core specification (FDN335N, FDN357N, IRLML2402TRPBF) are listed for reference but do not constitute direct substitutes.

Parameter Comparison

Part Number	Manufacturer	Vdss (V)	Id @ 25°C (A)	Rds On (mOhm)	Vgs(th) (V)	Qg (nC)	Ciss (pF)	Power Diss. (W)	Package	Status
AO3402	Alpha & Omega	30	4.0	55	1.4	4.34	390	1.4	SOT-23-3	Not For New Designs
AO3418	Alpha & Omega	30	3.8	60	1.8	3.2	270	1.4	SOT-23-3	Not For New Designs
AOSS32338C	Alpha & Omega	30	4.0	50	1.5	16	340	1.3	SOT-23-3	Active
DMG3418L-7	Diodes Inc.	30	4.0	60	1.5	5.5	464.3	1.4	SOT-23-3	Active
FDN337N	onsemi	30	2.2	65	1.0	9	300	0.5	SOT-23-3	Active
FDN357N	onsemi	30	1.9	60	2.0	5.9	235	0.5	SOT-23-3	Active
NTR4170NT1G	onsemi	30	2.4	55	1.4	4.76	432	0.48	SOT-23-3	Active
IRLML2502TRPBF	Infineon	20	4.2	45	1.2	12	740	1.25	SOT-23-3	Active
NTR4501NT1G	onsemi	20	3.2	80	1.2	6	200	1.25	SOT-23-3	Active
FDN335N	UMW	20	1.7	70	1.5	3.5	310	1.0	SOT-23	Active
IRLML2402TRPBF	Infineon	20	1.2	250	0.7	3.9	110	0.54	SOT-23-3	Not For New Designs

Engineering Selection Recommendations

Primary Substitutes (Recommended for Direct Replacement):

The AOSS32338C (Alpha & Omega) and DMG3418L-7 (Diodes Incorporated) are the preferred substitutes for the AO3402. Both devices maintain the 30V/4A specification, SOT-23-3 packaging, and -55°C to 150°C operating range. AOSS32338C carries Active product status, ensuring long-term availability and manufacturing support. DMG3418L-7 is also Active status and offers equivalent electrical performance. Both are ROHS3 compliant with MSL 1 rating, matching the AO3402 compliance profile.

Secondary Substitutes (Conditional Use):

The AO3418 (Alpha & Omega) provides a near-equivalent alternative with marginally reduced current rating (3.8A vs. 4A) and slightly higher on-resistance (60 mOhm vs. 55 mOhm). This part is suitable for applications where the full 4A specification is not required. However, AO3418 carries "Not For New Designs" status, limiting its suitability for long-term production.

Limited-Current Alternatives (30V Devices):

FDN337N and NTR4170NT1G maintain 30V Vdss but with reduced current ratings (2.2A and 2.4A respectively). These are suitable only for applications where continuous drain current does not exceed 2.4A. Both carry Active status and are ROHS3 compliant.

Voltage-Reduced Alternatives (20V Devices):

IRLML2502TRPBF and NTR4501NT1G are rated for 20V Vdss with current ratings of 4.2A and 3.2A respectively. These parts are suitable only for applications where the maximum operating voltage does not exceed 20V. Both are Active status and ROHS3 compliant.

Not Recommended:

FDN335N (P-Channel, 20V, 1.7A), FDN357N (30V, 1.9A), and IRLML2402TRPBF (20V, 1.2A) do not meet the core 30V/4A specification and are not suitable substitutes for the AO3402.

Frequently Asked Questions (FAQ)

Q: Can AOSS32338C directly replace AO3402 in existing designs?

A: Yes. AOSS32338C meets or exceeds all critical electrical parameters (30V Vdss, 4A Id, SOT-23-3 package) and maintains the same operating temperature range. AOSS32338C is Active status, providing better long-term availability than the AO3402 (Not For New Designs). Pin configuration and package dimensions are identical.

Q: What is the difference between AO3418 and AO3402?

A: AO3418 has a slightly lower continuous drain current rating (3.8A vs. 4A) and higher on-resistance (60 mOhm vs. 55 mOhm at 10V). Both share 30V Vdss, SOT-23-3 packaging, and identical operating temperature range. AO3418 is suitable for applications not requiring the full 4A specification. Both are "Not For New Designs" status.

Q: Can I use IRLML2502TRPBF as a substitute?

A: IRLML2502TRPBF is suitable only if your application voltage does not exceed 20V. This device is rated for 20V Vdss, whereas AO3402 is rated for 30V. Using a 20V-rated device in a 30V application risks device failure. IRLML2502TRPBF does provide 4.2A current capability and is Active status.

Q: Why do FDN337N and NTR4170NT1G have lower power dissipation ratings?

A: These devices have lower continuous drain current ratings (2.2A and 2.4A respectively) compared to the AO3402 (4A). Power dissipation is directly related to current-carrying capability. These parts are suitable only for lower-current applications.

Q: Are all substitute parts ROHS3 compliant?

A: Yes. All substitute parts listed in this document are ROHS3 compliant and carry MSL 1 (Unlimited) moisture sensitivity rating, matching the AO3402 compliance profile.

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

A: Active status indicates the manufacturer continues production and provides long-term availability support. "Not For New Designs" indicates the part is in end-of-life phase and may have limited future availability. For new designs, Active-status substitutes (AOSS32338C, DMG3418L-7) are preferred.

Q: Can I use DMG3418L-7 if my circuit is optimized for AO3402?

A: Yes, with minor circuit verification. DMG3418L-7 maintains identical Vdss (30V), Id (4A), and package (SOT-23-3). However, on-resistance is 60 mOhm vs. 55 mOhm, and gate charge is 5.5 nC vs. 4.34 nC. These differences may affect switching speed and thermal performance in high-frequency applications. Verify gate drive circuit compatibility and thermal margins.

Q: Is package compatibility guaranteed across all substitutes?

A: All substitutes listed use SOT-23-3 (or equivalent TO-236-3/SC-59) surface mount packaging with identical pin configuration. Physical dimensions and PCB footprints are compatible. However, input capacitance varies (235 pF to 464.3 pF), which may affect gate drive circuit performance in high-speed switching applications.

Q: What should I consider when selecting between AOSS32338C and DMG3418L-7?

A: Both are equivalent 30V/4A devices with Active status. AOSS32338C has lower on-resistance (50 mOhm vs. 60 mOhm) and lower gate charge (16 nC vs. 5.5 nC), providing better thermal and switching characteristics. DMG3418L-7 is from Diodes Incorporated, offering supply chain diversity. For thermal-critical applications, AOSS32338C is preferred. For supply chain redundancy, DMG3418L-7 is preferred.

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