BFT46 JFET N-Channel Equivalent & Substitute Parts

Part Overview

The BFT46 is an N-Channel JFET manufactured by NXP USA Inc., designed for low-current applications with a maximum drain current of 10 mA and 250 mW power dissipation in a surface mount SOT-23 package. The device is classified as obsolete, making substitute parts necessary for new designs and ongoing production requirements. Alternative components must maintain compatibility with the original electrical specifications and package form factor while meeting current availability and compliance standards.

Key Parameters

Parameter	Value	Unit
Drain to Source Voltage (Vdss)	25	V
Current - Drain (Id) - Max	10	mA
Current - Drain (Idss) @ Vds (Vgs=0)	200	µA @ 10 V
Voltage - Cutoff (VGS off) @ Id	1.2	V @ 0.5 nA
Input Capacitance (Ciss) (Max) @ Vds	5	pF @ 10V
Power - Max	250	mW
Operating Temperature (TJ)	150	°C
Package / Case	TO-236-3, SC-59, SOT-23-3	-
Mounting Type	Surface Mount	-

Substitute Part Grouping Explanation

Substitution of the BFT46 is determined by the following critical parameters:

Drain to Source Voltage (Vdss): Minimum 25 V required to maintain voltage headroom
Maximum Drain Current (Id): Must support at least 10 mA operation
Package Compatibility: SOT-23-3 (TO-236) form factor for direct PCB replacement
Power Dissipation: Minimum 225 mW to accommodate thermal requirements
Operating Temperature Range: Support for 150°C junction temperature
Compliance: RoHS3 compliance and REACH unaffected status required

Substitute parts are grouped into two categories:

Category A - Direct Electrical Equivalents: Parts with Vdss ≥ 25 V, Id ≥ 10 mA, and identical SOT-23-3 packaging. These provide seamless replacement with no circuit modifications required.

Category B - Enhanced Performance Alternatives: Parts with Vdss ≥ 25 V and higher current or power ratings in SOT-23-3 packaging. These offer improved performance margins and are suitable when circuit design permits higher current capability.

Parameter Comparison

Part Number	Manufacturer	Vdss (V)	Id Max (mA)	Idss @ Vds (µA)	VGS off (V)	Ciss Max (pF)	Power Max (mW)	Temp Range (°C)	Package	Status
BFT46	NXP USA Inc.	25	10	200 @ 10V	1.2 @ 0.5nA	5 @ 10V	250	-55 to 150	SOT-23-3	Obsolete
2SK3666-2-TB-E	onsemi	30	-	-	-	-	200	-	3CP	Obsolete
CPH3910-TL-E	onsemi	25	50	20 @ 5V	1.8 @ 100µA	6 @ 5V	400	-55 to 150	SOT-23-3	Active
MMBF4391LT1G	onsemi	30	-	50 @ 15V	4 @ 10nA	14 @ 15V	225	-55 to 150	SOT-23-3	Active
MMBF4392LT1G	onsemi	30	-	25 @ 15V	2 @ 10nA	14 @ 15V	225	-55 to 150	SOT-23-3	Active
MMBF4393LT1G	onsemi	30	-	5 @ 15V	0.5 @ 10nA	14 @ 15V	225	-55 to 150	SOT-23-3	Active
MMBF4393LT3G	onsemi	30	-	5 @ 15V	0.5 @ 10nA	14 @ 15V	225	-55 to 150	SOT-23-3	Active
MMBF4416	onsemi	30	15	-	-	-	-	-	SOT-23-3	Active
MMBF5457	onsemi	25	-	1 @ 15V	0.5 @ 10nA	7 @ 15V	350	-55 to 150	SOT-23-3	Active
MMBF5484	onsemi	25	5	-	-	-	-	-	SOT-23-3	Active
MMBF5485	onsemi	25	10	-	-	-	-	-	SOT-23-3	Active

Engineering Selection Recommendations

Primary Substitute - CPH3910-TL-E: This part meets all critical substitution criteria with Vdss of 25 V, maximum drain current of 50 mA (exceeding the 10 mA requirement), and identical SOT-23-3 packaging. The device is active status with full RoHS3 compliance and REACH unaffected certification. Operating temperature range matches the original specification at -55°C to 150°C. Higher power dissipation (400 mW) provides thermal margin.

Secondary Substitutes - MMBF4391LT1G, MMBF4392LT1G, MMBF4393LT1G, MMBF4393LT3G: These onsemi JFET N-Channel devices feature Vdss of 30 V with SOT-23-3 packaging and active product status. All meet RoHS3 and REACH requirements with -55°C to 150°C operating range. Idss characteristics vary across the series (50 mA, 25 mA, and 5 mA respectively), allowing selection based on specific circuit requirements.

Alternative - MMBF5457: Offers 25 V Vdss with 350 mW power dissipation and SOT-23-3 packaging. Active status with full compliance. Lower Idss (1 mA @ 15 V) suits applications requiring minimal leakage current.

RF Applications - MMBF4416, MMBF5484, MMBF5485: These RF-optimized JFET devices in SOT-23-3 packaging provide enhanced frequency performance (100 MHz to 400 MHz) with active status and compliance certifications. Suitable for high-frequency circuit substitution where RF characteristics are required.

Frequently Asked Questions (FAQ)

Q: Can CPH3910-TL-E directly replace BFT46 without circuit modifications?

A: Yes. CPH3910-TL-E maintains the same Vdss (25 V), exceeds the drain current requirement (50 mA vs. 10 mA), and uses identical SOT-23-3 packaging. No PCB layout changes are required.

Q: What is the difference between MMBF4391LT1G, MMBF4392LT1G, and MMBF4393LT1G?

A: These three devices differ in Idss characteristics: MMBF4391LT1G has 50 mA Idss, MMBF4392LT1G has 25 mA Idss, and MMBF4393LT1G has 5 mA Idss. All share 30 V Vdss and SOT-23-3 packaging. Selection depends on the circuit's leakage current tolerance.

Q: Why is 2SK3666-2-TB-E listed if it is also obsolete?

A: 2SK3666-2-TB-E is included for reference as a manufacturer-recommended substitute from the original BFT46 documentation. However, active alternatives such as CPH3910-TL-E are preferred for new designs due to ongoing availability.

Q: Are MMBF5484 and MMBF5485 suitable for general-purpose JFET applications?

A: MMBF5484 and MMBF5485 are RF-optimized devices with 400 MHz frequency capability. While they provide SOT-23-3 packaging and 25 V Vdss compatibility, they are designed for RF circuits. Use in general-purpose applications only if RF performance is not a design constraint.

Q: What compliance certifications apply to all active substitute parts?

A: All active substitute parts listed (CPH3910-TL-E, MMBF4391LT1G, MMBF4392LT1G, MMBF4393LT1G, MMBF4393LT3G, MMBF4416, MMBF5457, MMBF5484, MMBF5485) are RoHS3 compliant and REACH unaffected. Moisture sensitivity level is 1 (Unlimited) for all devices.

Q: Can parts with 30 V Vdss replace the 25 V BFT46?

A: Yes. Higher Vdss rating (30 V) provides additional voltage headroom and is electrically compatible. No circuit modifications are required. This applies to MMBF4391LT1G, MMBF4392LT1G, MMBF4393LT1G, MMBF4393LT3G, and MMBF4416.

Q: What is the recommended substitute for lowest leakage current applications?

A: MMBF4393LT1G and MMBF4393LT3G offer the lowest Idss at 5 mA @ 15 V among the listed substitutes. MMBF5457 provides even lower leakage at 1 mA @ 15 V, making it suitable for precision low-leakage circuit designs.

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