STB21NK50Z Equivalent & Substitute Parts

Part Overview

The STB21NK50Z is an N-Channel 500V 17A MOSFET manufactured by STMicroelectronics in the SuperMESH™ series, housed in a D2PAK surface mount package. This device is classified as obsolete, indicating discontinuation from the manufacturer. Alternative equivalent parts are necessary for new designs, production continuity, and long-term component availability. Substitute parts must maintain electrical compatibility across drain-source voltage, continuous drain current, on-resistance characteristics, and gate charge specifications while supporting the same D2PAK/TO-263 package footprint.

Key Parameters

Parameter	STB21NK50Z	Unit
Drain to Source Voltage (Vdss)	500	V
Continuous Drain Current (Id) @ 25°C	17	A
Rds On (Max) @ Id, Vgs	270 mOhm @ 8.5A, 10V	mOhm
Gate Charge (Qg) (Max) @ Vgs	119	nC @ 10V
Power Dissipation (Max)	190	W
Operating Temperature (TJ)	150	°C
Package Type	D2PAK (TO-263-3)	—
Vgs (Max)	±30	V
RoHS Status	ROHS3 Compliant	—
Moisture Sensitivity Level (MSL)	1 (Unlimited)	—

Substitute Part Grouping Explanation

Substitution eligibility for the STB21NK50Z is determined by the following critical parameters:

Mandatory Matching Criteria:

Drain to Source Voltage (Vdss): 500V (exact match required)
Package Type: D2PAK/TO-263-3 surface mount (mechanical compatibility)
Gate Drive Voltage: 10V (standard drive voltage)
Maximum Gate Voltage (Vgs): ±30V (gate interface compatibility)
RoHS3 Compliance and MSL Level 1 (regulatory and handling consistency)

Performance Compatibility Criteria:

Continuous Drain Current (Id): Equal to or greater than 17A
Rds On (Max): Equal to or less than 270 mOhm at specified conditions
Gate Charge (Qg): Lower values indicate faster switching; values up to 119 nC are acceptable
Power Dissipation: Equal to or greater than 190W supports thermal margin
Operating Temperature: Minimum 150°C (TJ) required

The five substitute parts listed below satisfy all mandatory criteria and maintain electrical performance within acceptable ranges for direct substitution in applications designed for the STB21NK50Z.

Parameter Comparison

Parameter	STB21NK50Z (STMicroelectronics)	FDB20N50F (onsemi)	IXFA16N50P (IXYS)	IXFA26N50P3 (IXYS)	IXTA16N50P (IXYS)	IXTA460P2 (IXYS)	Unit
Vdss	500	500	500	500	500	500	V
Id @ 25°C (Tc)	17	20	16	26	16	24	A
Rds On (Max) @ 10V	270 @ 8.5A	260 @ 10A	400 @ 8A	230 @ 13A	400 @ 8A	270 @ 12A	mOhm
Qg (Max) @ 10V	119	65	43	42	43	48	nC
Power Dissipation (Max)	190	250	300	500	300	480	W
Operating Temperature (TJ)	150	−55 to 150	−55 to 150	−55 to 150	−55 to 150	−55 to 150	°C
Vgs (Max)	±30	±30	±30	±30	±30	±30	V
Package	D2PAK (TO-263-3)	TO-263 (D2PAK)	TO-263AA (IXFA)	TO-263AA (IXFA)	TO-263AA	TO-263AA	—
RoHS Status	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	—
MSL	1 (Unlimited)	1 (Unlimited)	1 (Unlimited)	1 (Unlimited)	1 (Unlimited)	1 (Unlimited)	—

Engineering Selection Recommendations

FDB20N50F (onsemi) — Active product status with 20A continuous drain current and 250W power dissipation. Rds On of 260 mOhm at 10A, 10V provides equivalent on-resistance performance to the STB21NK50Z. Lower gate charge (65 nC) enables faster switching transitions. Extended operating temperature range (−55°C to 150°C) supports broader thermal environments. Recommended for applications requiring active product support and higher current margin.

IXFA26N50P3 (IXYS) — Active product status with highest current rating (26A) and power dissipation (500W) among substitutes. Rds On of 230 mOhm at 13A, 10V provides superior on-resistance characteristics. Lowest gate charge (42 nC) among all options enables fastest switching performance. Suitable for applications requiring maximum thermal and current headroom with enhanced efficiency.

IXFA16N50P (IXYS) — Active product status with 16A continuous drain current and 300W power dissipation. Rds On of 400 mOhm at 8A, 10V represents higher on-resistance than the STB21NK50Z. Gate charge of 43 nC provides fast switching. Acceptable for applications where the 16A current rating meets design requirements and higher on-resistance is tolerable.

IXTA16N50P (IXYS) — Active product status with identical electrical specifications to IXFA16N50P (16A, 300W, 400 mOhm Rds On, 43 nC Qg). Represents alternative IXYS product line within the Polar series. Suitable for applications with equivalent current and thermal requirements as IXFA16N50P.

IXTA460P2 (IXYS) — Last Time Buy product status with 24A continuous drain current and 480W power dissipation. Rds On of 270 mOhm at 12A, 10V matches the STB21NK50Z on-resistance specification. Gate charge of 48 nC provides acceptable switching performance. Suitable for near-term applications; long-term availability is limited due to Last Time Buy status.

Frequently Asked Questions (FAQ)

Q: Can the STB21NK50Z be directly replaced with any of these substitute parts?

A: Direct replacement is possible only when the application circuit and thermal design accommodate the electrical differences. All substitutes maintain the 500V Vdss rating and D2PAK package compatibility. However, differences in continuous drain current, on-resistance, and gate charge require circuit validation. Applications with tight thermal budgets or current margins must account for these variations.

Q: What is the significance of the different drain current ratings among substitutes?

A: The STB21NK50Z is rated for 17A continuous drain current. Substitutes range from 16A to 26A. Parts rated below 17A (IXFA16N50P, IXTA16N50P at 16A) operate with reduced current margin and may not be suitable for applications designed to the full 17A specification. Parts rated above 17A (FDB20N50F at 20A, IXTA460P2 at 24A, IXFA26N50P3 at 26A) provide current margin and are preferred for direct substitution.

Q: How does on-resistance (Rds On) affect circuit performance?

A: On-resistance directly impacts power dissipation and heat generation. The STB21NK50Z specifies 270 mOhm at 8.5A, 10V. Substitutes with lower Rds On (FDB20N50F at 260 mOhm, IXFA26N50P3 at 230 mOhm, IXTA460P2 at 270 mOhm) reduce conduction losses and improve efficiency. Substitutes with higher Rds On (IXFA16N50P and IXTA16N50P at 400 mOhm) increase power dissipation and require thermal design verification.

Q: What does gate charge (Qg) indicate, and why do lower values matter?

A: Gate charge represents the total charge required to switch the MOSFET from off to on state. Lower gate charge enables faster switching transitions and reduces gate driver power consumption. The STB21NK50Z specifies 119 nC. All substitutes feature lower gate charge (42 to 65 nC), resulting in faster switching performance and reduced driver stress.

Q: Are all substitute parts available in the same package?

A: All substitute parts use D2PAK or TO-263-3 surface mount packages with identical pin configurations (2 leads + tab). Package footprints are mechanically compatible, allowing direct PCB layout substitution without redesign.

Q: What is the difference between active and obsolete product status?

A: The STB21NK50Z is obsolete, meaning STMicroelectronics no longer manufactures or supports this part. Active substitutes (FDB20N50F, IXFA16N50P, IXFA26N50P3, IXTA16N50P) are currently produced and supported by their manufacturers. IXTA460P2 carries Last Time Buy status, indicating limited future availability. For new designs, active products are preferred for long-term supply assurance.

Q: Do all substitutes meet the same regulatory and compliance standards?

A: Yes. All substitute parts are ROHS3 compliant and carry MSL Level 1 (Unlimited) moisture sensitivity rating, matching the STB21NK50Z specifications. All parts are classified under ECCN EAR99 and HTSUS 8541.29.0095, ensuring consistent regulatory treatment.

Q: Which substitute is the best choice for a direct replacement?

A: Selection depends on application requirements. FDB20N50F (onsemi) offers active status with improved specifications and higher current rating (20A). IXFA26N50P3 (IXYS) provides maximum performance margin with 26A rating and lowest on-resistance (230 mOhm). IXTA460P2 (IXYS) matches the original on-resistance specification (270 mOhm) but carries Last Time Buy status. Evaluate current requirements, thermal budget, and long-term availability needs for your specific application.

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