STB78NF55-08 Equivalent & Substitute Parts

Part Overview

The STB78NF55-08 is an N-Channel MOSFET manufactured by STMicroelectronics, rated for 55V drain-to-source voltage and 80A continuous drain current at 25°C. This device is part of the STripFET™ II series and is packaged in the TO-263 (D2PAK) surface mount configuration. The part is classified as obsolete, making identification of equivalent and substitute components necessary for ongoing design support, production continuity, and system maintenance. Substitute parts must maintain electrical compatibility across critical parameters including voltage rating, current capacity, on-resistance characteristics, and thermal performance while accommodating the same or compatible package footprints.

Key Parameters

Parameter	Value	Unit
Drain to Source Voltage (Vdss)	55	V
Continuous Drain Current (Id) @ 25°C	80	A (Tc)
Rds On (Max) @ 40A, 10V	8	mOhm
Gate Threshold Voltage (Vgs(th)) @ 250µA	4	V
Gate Charge (Qg) @ 10V	155	nC
Power Dissipation (Max)	300	W (Tc)
Operating Temperature Range	-55 to 175	°C (TJ)
Package Type	TO-263 (D2PAK)	Surface Mount

Substitute Part Grouping Explanation

Substitution of the STB78NF55-08 is determined by strict adherence to the following electrical and mechanical parameters:

Primary Substitution Criteria:

Drain-to-Source Voltage (Vdss): Must equal or exceed 55V
Continuous Drain Current (Id): Must meet or exceed 80A at 25°C
Package Type: Must be compatible with TO-263 (D2PAK) footprint
Operating Temperature Range: Must span -55°C to 175°C
RoHS and REACH Compliance: Must maintain ROHS3 Compliant and REACH Unaffected status

Secondary Compatibility Parameters:

On-Resistance (Rds On): Lower or equivalent values ensure thermal performance
Gate Charge (Qg): Lower values reduce switching losses
Input Capacitance (Ciss): Affects gate drive requirements
Gate Threshold Voltage (Vgs(th)): Must be compatible with existing gate drive circuits

The identified substitute parts meet these criteria while accommodating variations in power dissipation ratings and specific on-resistance measurements at different test conditions.

Parameter Comparison

Parameter	STB78NF55-08 (Main)	BUK9612-55B,118	IXTA90N055T2	Unit
Manufacturer	STMicroelectronics	Nexperia USA Inc.	IXYS	—
Product Status	Obsolete	Active	Active	—
Drain to Source Voltage (Vdss)	55	55	55	V
Continuous Drain Current (Id) @ 25°C	80	75	90	A (Tc)
Rds On (Max) @ 10V	8 @ 40A	10 @ 25A	8.4 @ 25A	mOhm
Gate Threshold Voltage (Vgs(th))	4 @ 250µA	2 @ 1mA	4 @ 250µA	V
Gate Charge (Qg) @ Vgs	155 @ 10V	31 @ 5V	42 @ 10V	nC
Input Capacitance (Ciss) @ 25V	3740	3693	2770	pF
Power Dissipation (Max)	300	157	150	W (Tc)
Operating Temperature Range	-55 to 175	-55 to 175	-55 to 175	°C (TJ)
Package Type	TO-263 (D2PAK)	D2PAK	TO-263AA	—
RoHS Status	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	—
REACH Status	REACH Unaffected	REACH Unaffected	REACH Unaffected	—

Engineering Selection Recommendations

BUK9612-55B,118 (Nexperia USA Inc.)

This substitute is an active product with AEC-Q101 automotive qualification. It maintains the 55V voltage rating and D2PAK package compatibility. The continuous drain current rating of 75A is 6.25% lower than the STB78NF55-08, which may require thermal analysis in high-current applications. The on-resistance of 10mOhm at 25A, 10V is slightly higher than the main part. Gate charge is significantly lower at 31nC, reducing switching losses. This part is suitable for applications where the 75A rating is sufficient and automotive-grade reliability is required.

IXTA90N055T2 (IXYS)

This substitute is an active product from the TrenchT2™ series. It exceeds the STB78NF55-08 in continuous drain current with a 90A rating, providing 12.5% additional current capacity. The on-resistance of 8.4mOhm at 25A, 10V is comparable to the main part. Gate charge is lower at 42nC, and input capacitance is reduced to 2770pF, both favorable for switching performance. The TO-263AA package is compatible with the D2PAK footprint. Power dissipation is rated at 150W, which is lower than the main part but sufficient for most applications within the 90A operating envelope. This part is suitable for applications requiring higher current capacity with improved switching characteristics.

Both substitute parts maintain full compliance with RoHS3 and REACH requirements, operate across the same temperature range, and are available in compatible surface mount packages.

Frequently Asked Questions (FAQ)

Q: Can the BUK9612-55B,118 be used as a direct replacement for the STB78NF55-08?

A: The BUK9612-55B,118 is electrically compatible for applications operating at or below 75A continuous drain current. Both parts share the 55V voltage rating, D2PAK package footprint, and identical operating temperature range. The slightly higher on-resistance (10mOhm vs. 8mOhm) requires verification that thermal performance remains acceptable in the target application. The lower gate charge of the BUK9612-55B,118 may reduce switching losses.

Q: Is the IXTA90N055T2 a suitable replacement when higher current capacity is needed?

A: Yes. The IXTA90N055T2 provides 90A continuous drain current, exceeding the STB78NF55-08 by 12.5%. It maintains the 55V voltage rating and TO-263AA package compatibility. The on-resistance and gate charge characteristics are favorable. Applications requiring sustained currents above 80A benefit from this higher-rated device.

Q: Are all three parts compatible with the same PCB footprint?

A: The STB78NF55-08, BUK9612-55B,118, and IXTA90N055T2 all use TO-263 (D2PAK) or equivalent surface mount packages with identical lead configurations. PCB footprints designed for the STB78NF55-08 accommodate both substitute parts without modification.

Q: What is the impact of different gate charge values on circuit design?

A: Gate charge affects the energy required to switch the MOSFET and influences switching speed. The BUK9612-55B,118 (31nC) and IXTA90N055T2 (42nC) both have lower gate charge than the STB78NF55-08 (155nC), resulting in reduced switching losses and potentially faster switching transitions. Existing gate drive circuits designed for the STB78NF55-08 operate safely with these lower gate charge values.

Q: Do all substitute parts meet the same compliance standards?

A: Yes. All three parts are ROHS3 Compliant and REACH Unaffected. The BUK9612-55B,118 carries additional AEC-Q101 automotive qualification, making it suitable for automotive applications requiring this certification.

Q: What thermal considerations apply when selecting between these parts?

A: The STB78NF55-08 is rated for 300W maximum power dissipation. The BUK9612-55B,118 and IXTA90N055T2 are rated at 157W and 150W respectively. In applications approaching the 80A rating of the main part, thermal management becomes critical. The lower power dissipation ratings of the substitutes reflect their lower current ratings and require verification that the application's thermal design remains adequate.

Q: Can gate drive circuits designed for the STB78NF55-08 be used with the substitutes without modification?

A: Yes. All three parts share compatible gate threshold voltage characteristics and maximum gate voltage ratings (±20V for STB78NF55-08 and IXTA90N055T2; ±15V for BUK9612-55B,118). Existing gate drive circuits operate with all three parts. The lower gate charge of the substitutes may improve switching performance without requiring circuit changes.

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