FMMT634TC Equivalent & Substitute Parts

Part Overview

The FMMT634TC is an NPN Darlington bipolar junction transistor manufactured by Diodes Incorporated, designed for surface mount applications in the SOT-23-3 package. This component operates at a maximum collector voltage of 100 V with a collector current rating of 900 mA and a maximum power dissipation of 625 mW. The FMMT634TC is classified as obsolete, necessitating identification of equivalent and substitute parts for ongoing design requirements and production continuity.

Key Parameters

Parameter	Value	Unit
Transistor Type	NPN - Darlington	—
Current - Collector (Ic) (Max)	900	mA
Voltage - Collector Emitter Breakdown (Max)	100	V
Vce Saturation (Max) @ Ib, Ic	960 mV @ 5 mA, 1 A	—
Current - Collector Cutoff (Max)	100	nA
DC Current Gain (hFE) (Min) @ Ic, Vce	20000 @ 100 mA, 5 V	—
Power - Max	625	mW
Frequency - Transition	140	MHz
Operating Temperature Range	-55 to 150	°C (TJ)
Package / Case	SOT-23-3	—
Mounting Type	Surface Mount	—
RoHS Status	ROHS3 Compliant	—
Moisture Sensitivity Level (MSL)	1 (Unlimited)	—

Substitute Part Grouping Explanation

Substitution of the FMMT634TC is determined by electrical and mechanical compatibility across the following critical parameters:

Primary Substitution Criteria:

Transistor Type: NPN - Darlington configuration
Package / Case: SOT-23-3 surface mount package
Current - Collector (Ic) (Max): 900 mA minimum
Voltage - Collector Emitter Breakdown (Max): 100 V minimum
DC Current Gain (hFE) (Min): 20000 @ 100 mA, 5 V minimum
Operating Temperature Range: -55°C to 150°C (TJ)
RoHS3 Compliance and MSL Level 1

Direct Equivalents maintain identical electrical specifications and packaging, differing only in product status or packaging format (bulk versus tape & reel).

Parametric Equivalents maintain the same base electrical performance characteristics and package type, with variations in power dissipation or packaging configuration that do not affect functional compatibility in standard applications.

Manufacturer-Recommended Alternatives are from different manufacturers but operate within the same functional envelope, though with reduced voltage or current ratings that require circuit-level evaluation for specific applications.

Parameter Comparison

Parameter	FMMT634TC	FMMT634QTA	FMMT634TA	2SD1383KT146B	2SD2142KT146
Manufacturer	Diodes Incorporated	Diodes Incorporated	Diodes Incorporated	Rohm Semiconductor	Rohm Semiconductor
Transistor Type	NPN - Darlington	NPN - Darlington	NPN - Darlington	NPN - Darlington	NPN - Darlington
Current - Collector (Ic) (Max)	900 mA	900 mA	900 mA	300 mA	300 mA
Voltage - Collector Emitter Breakdown (Max)	100 V	100 V	100 V	32 V	30 V
Vce Saturation (Max) @ Ib, Ic	960 mV @ 5 mA, 1 A	960 mV @ 5 mA, 1 A	960 mV @ 5 mA, 1 A	1.5 V @ 400 µA, 200 mA	1.5 V @ 100 µA, 100 mA
Current - Collector Cutoff (Max)	100 nA	100 nA	100 nA	1 µA	100 nA
DC Current Gain (hFE) (Min) @ Ic, Vce	20000 @ 100 mA, 5 V	20000 @ 100 mA, 5 V	20000 @ 100 mA, 5 V	5000 @ 100 mA, 5 V	10000 @ 100 mA, 5 V
Power - Max	625 mW	806 mW	625 mW	200 mW	200 mW
Frequency - Transition	140 MHz	140 MHz	140 MHz	250 MHz	200 MHz
Operating Temperature Range	-55 to 150 °C (TJ)	-55 to 150 °C (TJ)	-55 to 150 °C (TJ)	150 °C (TJ)	150 °C (TJ)
Package / Case	SOT-23-3	SOT-23-3	SOT-23-3	SOT-23-3	SOT-23-3
Mounting Type	Surface Mount	Surface Mount	Surface Mount	Surface Mount	Surface Mount
Product Status	Obsolete	Active	Active	Active	Active
RoHS Status	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant
Moisture Sensitivity Level (MSL)	1 (Unlimited)	1 (Unlimited)	1 (Unlimited)	1 (Unlimited)	1 (Unlimited)

Engineering Selection Recommendations

Direct Substitutes (Diodes Incorporated FMMT634 Series):

The FMMT634QTA and FMMT634TA are direct substitutes for the obsolete FMMT634TC. Both parts maintain identical electrical specifications including 900 mA collector current, 100 V breakdown voltage, 20000 hFE minimum gain, and SOT-23-3 packaging. The FMMT634QTA is supplied in tape & reel format with 806 mW power rating, while the FMMT634TA is supplied in tape & reel format with 625 mW power rating matching the original specification. Both parts are active products with ROHS3 compliance and MSL Level 1 rating, ensuring long-term availability and regulatory compliance.

Manufacturer-Recommended Alternatives (Rohm Semiconductor):

The 2SD1383KT146B and 2SD2142KT146 are manufacturer-recommended alternatives from Rohm Semiconductor. These parts are active products with ROHS3 compliance and MSL Level 1 rating. However, these alternatives operate at reduced voltage and current ratings: 32 V / 300 mA (2SD1383KT146B) and 30 V / 300 mA (2SD2142KT146), compared to the original 100 V / 900 mA specification. These alternatives are suitable only for applications where the reduced voltage and current ratings are compatible with circuit requirements. The 2SD1383KT146B offers higher transition frequency (250 MHz) and the 2SD2142KT146 offers intermediate transition frequency (200 MHz) compared to the original 140 MHz.

Recommendation Priority:

For direct replacement in existing designs, select FMMT634QTA or FMMT634TA based on packaging requirements (tape & reel format). For new designs or applications with reduced voltage and current requirements, the Rohm alternatives provide active product status with enhanced frequency performance.

Frequently Asked Questions (FAQ)

Q: Can the FMMT634QTA directly replace the FMMT634TC in existing designs?

A: Yes. The FMMT634QTA maintains identical electrical specifications (900 mA, 100 V, 20000 hFE) and SOT-23-3 packaging. The primary difference is packaging format (tape & reel versus bulk) and slightly higher power rating (806 mW versus 625 mW), which does not affect functional compatibility.

Q: What is the difference between FMMT634QTA and FMMT634TA?

A: Both are Diodes Incorporated products with identical electrical specifications and SOT-23-3 packaging. The FMMT634QTA has a power rating of 806 mW, while the FMMT634TA has a power rating of 625 mW matching the original FMMT634TC. Both are supplied in tape & reel format and are active products.

Q: Can the Rohm 2SD1383KT146B or 2SD2142KT146 replace the FMMT634TC?

A: These parts are not direct replacements. They operate at reduced voltage (32 V and 30 V respectively) and reduced current (300 mA) compared to the original 100 V / 900 mA specification. They are suitable only for applications where these reduced ratings are compatible with circuit requirements. Both maintain NPN Darlington configuration and SOT-23-3 packaging.

Q: Are all substitute parts RoHS3 compliant?

A: Yes. All listed substitute parts (FMMT634QTA, FMMT634TA, 2SD1383KT146B, and 2SD2142KT146) are ROHS3 compliant with MSL Level 1 rating, ensuring regulatory compliance and unlimited moisture sensitivity handling.

Q: What is the operating temperature range for substitute parts?

A: The Diodes Incorporated substitutes (FMMT634QTA and FMMT634TA) maintain the original operating range of -55°C to 150°C (TJ). The Rohm alternatives (2SD1383KT146B and 2SD2142KT146) are rated to 150°C (TJ) maximum, without specified minimum temperature in the provided data.

Q: How do the transition frequencies compare?

A: The original FMMT634TC operates at 140 MHz. The Diodes substitutes (FMMT634QTA and FMMT634TA) maintain 140 MHz. The Rohm alternatives offer higher transition frequencies: 2SD1383KT146B at 250 MHz and 2SD2142KT146 at 200 MHz.

Q: What packaging formats are available?

A: All substitute parts are supplied in SOT-23-3 surface mount package. The FMMT634QTA and FMMT634TA are supplied in tape & reel format. The 2SD1383KT146B and 2SD2142KT146 are supplied in cut tape and Digi-Reel format.

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