FQB4N90TM Equivalent & Substitute Parts

Part Overview

The FQB4N90TM is an N-Channel MOSFET manufactured by onsemi, rated for 900V drain-to-source voltage with a continuous drain current of 4.2A at 25°C. This device is housed in a Surface Mount TO-263 (D2PAK) package and is part of the QFET® series. The FQB4N90TM is classified as obsolete, making identification of equivalent substitute parts essential for ongoing design support, production continuity, and system maintenance. Substitute parts must maintain electrical compatibility across voltage ratings, current handling, thermal characteristics, and package specifications to ensure direct replacement capability.

Key Parameters

Parameter	Value	Unit
Drain to Source Voltage (Vdss)	900	V
Continuous Drain Current (Id) @ 25°C	4.2	A (Tc)
On-State Resistance (Rds On Max) @ Id, Vgs	3.3 @ 2.1A, 10V	Ohm
Gate Threshold Voltage (Vgs(th) Max) @ Id	5 @ 250µA	V
Gate Charge (Qg Max) @ Vgs	30 @ 10V	nC
Maximum Gate Voltage (Vgs Max)	±30	V
Input Capacitance (Ciss Max) @ Vds	1100 @ 25V	pF
Power Dissipation (Max)	3.13 (Ta), 140 (Tc)	W
Operating Temperature Range	-55 to 150	°C (TJ)
Package Type	TO-263 (D2PAK)	Surface Mount
Moisture Sensitivity Level (MSL)	1	Unlimited

Substitute Part Grouping Explanation

Substitution of the FQB4N90TM is determined by strict electrical and mechanical parameter alignment. The primary substitute identified is the STB6NK90ZT4 from STMicroelectronics. This substitution is valid based on the following critical parameters:

Electrical Compatibility Criteria:

Drain-to-Source Voltage (Vdss): Both devices rated at 900V, ensuring equivalent voltage withstand capability
Package Type: Both use TO-263 (D2PAK) Surface Mount configuration, enabling direct mechanical replacement
Gate Voltage Range (Vgs Max): Both support ±30V maximum gate voltage
Operating Temperature Range: Both operate across -55°C to 150°C (TJ)
Technology: Both are Metal Oxide MOSFET (MOSFET) N-Channel devices

Performance Enhancement Parameters:

The STB6NK90ZT4 provides higher continuous drain current (5.8A vs 4.2A), lower on-state resistance (2Ohm vs 3.3Ohm), and improved thermal performance (140W Tc rating maintained)
These enhancements represent superior performance characteristics while maintaining full backward compatibility

Compliance and Availability:

STB6NK90ZT4 is Active product status with significantly higher inventory availability (105,400 pcs vs 2,320 pcs)
Both devices maintain REACH Unaffected status and EAR99 ECCN classification

Parameter Comparison

Parameter	FQB4N90TM (onsemi)	STB6NK90ZT4 (STMicroelectronics)	Unit
FET Type	N-Channel	N-Channel	—
Technology	MOSFET (Metal Oxide)	MOSFET (Metal Oxide)	—
Drain to Source Voltage (Vdss)	900	900	V
Continuous Drain Current (Id) @ 25°C	4.2	5.8	A (Tc)
Drive Voltage (Max Rds On)	10	10	V
Rds On (Max) @ Id, Vgs	3.3 @ 2.1A, 10V	2 @ 2.9A, 10V	Ohm
Vgs(th) (Max) @ Id	5 @ 250µA	4.5 @ 100µA	V
Gate Charge (Qg) (Max) @ Vgs	30 @ 10V	60.5 @ 10V	nC
Vgs (Max)	±30	±30	V
Input Capacitance (Ciss) (Max) @ Vds	1100 @ 25V	1350 @ 25V	pF
Power Dissipation (Max)	3.13 (Ta), 140 (Tc)	140 (Tc)	W
Operating Temperature	-55 to 150	-55 to 150	°C (TJ)
Mounting Type	Surface Mount	Surface Mount	—
Package / Case	TO-263-3, D2PAK	TO-263-3, D2PAK	—
Moisture Sensitivity Level (MSL)	1 (Unlimited)	1 (Unlimited)	—
REACH Status	REACH Unaffected	REACH Unaffected	—
ECCN	EAR99	EAR99	—

Engineering Selection Recommendations

Primary Substitute: STB6NK90ZT4

The STB6NK90ZT4 is the qualified substitute for the obsolete FQB4N90TM. Selection of this substitute is based on the following engineering factors:

Product Status and Lifecycle: The FQB4N90TM is classified as obsolete, creating supply chain risk. The STB6NK90ZT4 maintains Active product status with robust inventory availability (105,400 pcs), ensuring long-term procurement viability and production continuity.

Electrical Equivalence: Both devices share identical voltage ratings (900V Vdss) and operating temperature ranges (-55°C to 150°C TJ). The STB6NK90ZT4 exceeds the FQB4N90TM in current-handling capability (5.8A vs 4.2A) and provides superior on-state resistance performance (2Ohm vs 3.3Ohm at comparable conditions). These characteristics ensure the substitute operates within or exceeds the original design envelope.

Package and Mechanical Compatibility: Both devices utilize the TO-263 (D2PAK) Surface Mount package configuration, enabling direct board-level replacement without PCB redesign or mechanical rework.

Regulatory and Compliance Alignment: Both parts maintain REACH Unaffected status and EAR99 ECCN classification, ensuring equivalent regulatory compliance. The STB6NK90ZT4 carries RoHS3 Compliance certification, providing additional environmental compliance assurance.

Thermal Performance: Both devices support 140W power dissipation at Tc, maintaining thermal design margins established for the original FQB4N90TM.

Frequently Asked Questions (FAQ)

Q: Can the STB6NK90ZT4 directly replace the FQB4N90TM without circuit modification?

A: Yes. Both devices share identical voltage ratings (900V Vdss), gate voltage specifications (±30V Vgs Max), operating temperature ranges (-55°C to 150°C TJ), and TO-263 (D2PAK) package configuration. The STB6NK90ZT4 provides enhanced performance characteristics (higher current rating and lower on-state resistance) that are fully backward compatible with circuits designed for the FQB4N90TM.

Q: What are the key differences between these two devices?

A: The STB6NK90ZT4 provides superior electrical performance: continuous drain current of 5.8A versus 4.2A, on-state resistance of 2Ohm versus 3.3Ohm, and lower gate threshold voltage (4.5V versus 5V). The STB6NK90ZT4 exhibits higher gate charge (60.5nC versus 30nC) and input capacitance (1350pF versus 1100pF). These differences represent performance enhancements rather than incompatibilities.

Q: Are there package compatibility concerns?

A: No. Both the FQB4N90TM and STB6NK90ZT4 use the TO-263-3 (D2PAK) Surface Mount package with identical pinout and lead configuration. Direct PCB substitution is possible without layout modifications.

Q: What is the moisture sensitivity level for both devices?

A: Both devices are classified as MSL 1 (Unlimited), indicating no moisture sensitivity restrictions. Standard handling and storage procedures apply to both parts.

Q: Are there regulatory or compliance differences?

A: Both devices maintain REACH Unaffected status and EAR99 ECCN classification. The STB6NK90ZT4 additionally carries RoHS3 Compliance certification. No regulatory barriers exist to substitution.

Q: Why is the STB6NK90ZT4 recommended over the FQB4N90TM?

A: The FQB4N90TM is classified as obsolete with limited inventory (2,320 pcs). The STB6NK90ZT4 is Active product status with significantly higher availability (105,400 pcs), ensuring long-term supply chain security and production continuity. The substitute provides equivalent or superior electrical performance across all critical parameters.

Q: What is the gate charge difference and does it affect circuit design?

A: The STB6NK90ZT4 has higher gate charge (60.5nC versus 30nC at 10V Vgs). This parameter affects gate driver design and switching speed characteristics. Circuits designed for the FQB4N90TM will operate with the STB6NK90ZT4, though gate drive timing may differ slightly. Verification of gate driver performance is within normal design validation procedures.

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