SMAJ33 Transient Voltage Suppressor (TVS) Diode – Equivalent & Substitute Parts

Part Overview

The SMAJ33 is a unidirectional Zener-type transient voltage suppressor manufactured by Littelfuse Inc., designed for general-purpose overvoltage protection in surface-mount applications. Specified with a 33V reverse standoff voltage, 55.97V maximum clamping voltage, and 7.5A peak pulse current in a DO-214AC (SMA) package, this component is classified as obsolete. Due to its discontinued status, equivalent and substitute parts from active manufacturers are necessary to maintain design continuity and ensure supply chain availability for new production and field replacements.

Key Parameters

Parameter	Value	Unit
Voltage – Reverse Standoff (Typ)	33	V
Voltage – Breakdown (Min)	34.79	V
Voltage – Clamping (Max) @ Ipp	55.97	V
Current – Peak Pulse (10/1000µs)	7.5	A
Power – Peak Pulse	400	W
Operating Temperature Range	-65 to 150	°C (TJ)
Package / Case	DO-214AC, SMA	—
Type	Zener	—
Unidirectional Channels	1	—
RoHS Status	ROHS3 Compliant	—
Moisture Sensitivity Level (MSL)	1 (Unlimited)	—

Substitute Part Grouping Explanation

Substitution eligibility for the SMAJ33 is determined by the following critical parameters:

Reverse Standoff Voltage: Must be 33V (±tolerance as specified by manufacturer)
Package / Case: Must be DO-214AC (SMA) for mechanical and thermal compatibility
Type: Must be Zener unidirectional TVS diode
Unidirectional Channels: Must be 1
Clamping Voltage (Max) @ Ipp: Acceptable range 53.3V to 59V (within design margin of original 55.97V specification)
Peak Pulse Current: Acceptable range 7.5A to 11.3A (original specification 7.5A; higher ratings provide design margin)
Power – Peak Pulse: Acceptable range 400W to 600W
Operating Temperature Range: Must support minimum -55°C to 150°C; extended ranges (-65°C) are acceptable
RoHS Compliance: ROHS3 Compliant required
Product Status: Active status preferred for long-term availability

Substitute parts meeting these criteria are functionally equivalent and mechanically interchangeable with the SMAJ33 in the specified application.

Parameter Comparison

Part Number	Manufacturer	Voltage – Reverse Standoff (V)	Voltage – Clamping (Max) @ Ipp (V)	Current – Peak Pulse (A)	Power – Peak Pulse (W)	Operating Temperature (°C)	Product Status	RoHS Status
SMAJ33	Littelfuse Inc.	33	55.97	7.5	400	-65 to 150	Obsolete	ROHS3 Compliant
SMAJ33A	MDD	33	53.3	7.5	400	-50 to 150	Active	ROHS3 Compliant
SZ1SMA33AT3G	Littelfuse Inc.	33	53.3	7.5	400	-65 to 150	Active	ROHS3 Compliant
SMA6J33A-TP	Micro Commercial Co	33	53.3	11.3	600	-55 to 175	Active	ROHS3 Compliant
SMAJ33A-13-F	Diodes Incorporated	33	53.3	7.5	400	-55 to 150	Active	ROHS3 Compliant
SMAJ33A-TP	Micro Commercial Co	33	53.3	7.5	400	-55 to 175	Active	ROHS3 Compliant
SMAJ33AE3/TR13	Microchip Technology	33	53.3	9.4	500	-65 to 150	Active	ROHS3 Compliant
SMAJ33E3/TR13	Microchip Technology	33	59	8.5	500	-65 to 150	Active	ROHS3 Compliant
TV04A330J-G	Comchip Technology	33	53.3	7.5	400	-55 to 150	Active	ROHS3 Compliant

Engineering Selection Recommendations

All listed substitute parts are active products with ROHS3 compliance and meet the core electrical and mechanical requirements of the SMAJ33. Selection should prioritize the following factors:

Primary Selection Criteria:

SZ1SMA33AT3G (Littelfuse Inc.): Maintains original manufacturer continuity with active product status, identical operating temperature range (-65°C to 150°C), and AEC-Q101 automotive qualification. Recommended for applications requiring automotive-grade reliability.
SMAJ33A-TP (Micro Commercial Co): Active product with extended operating temperature range (-55°C to 175°C), providing thermal margin for demanding environments. Tape & Reel packaging supports high-volume production.
SMAJ33AE3/TR13 (Microchip Technology): Active product with identical temperature range to original (-65°C to 150°C) and higher peak pulse current (9.4A), offering design margin for transient protection.
SMA6J33A-TP (Micro Commercial Co): Highest power rating (600W) and peak pulse current (11.3A) among substitutes, suitable for applications requiring enhanced surge protection capability.

All substitute parts are mechanically and electrically compatible with the SMAJ33 in DO-214AC (SMA) package applications. Selection among these options depends on specific supply chain availability, packaging requirements (Tape & Reel vs. Bulk), and thermal operating conditions of the target application.

Frequently Asked Questions (FAQ)

Q: Can SMAJ33 substitutes be used interchangeably in existing designs?

A: Yes, all listed substitute parts maintain the same 33V reverse standoff voltage, DO-214AC (SMA) package, and unidirectional Zener topology. Mechanical and electrical interchangeability is confirmed. Verify clamping voltage tolerance requirements for your specific circuit design, as some substitutes specify 53.3V versus the original 55.97V.

Q: What is the difference between clamping voltage specifications (53.3V vs. 55.97V vs. 59V)?

A: Clamping voltage is the maximum voltage across the TVS diode during a transient event at peak pulse current. The original SMAJ33 specifies 55.97V maximum. Substitutes with 53.3V provide tighter clamping (lower voltage stress on protected circuits), while SMAJ33E3/TR13 at 59V provides looser clamping. All values remain within acceptable protection margins for 33V standoff applications.

Q: Are there temperature range differences between substitutes?

A: Yes. The original SMAJ33 and SZ1SMA33AT3G support -65°C to 150°C. Most other substitutes support -55°C to 150°C or -55°C to 175°C. For applications requiring -65°C operation, select SZ1SMA33AT3G, SMAJ33AE3/TR13, or SMAJ33E3/TR13.

Q: What does "Peak Pulse Current" variation mean for my application?

A: Peak pulse current (7.5A to 11.3A across substitutes) indicates the maximum transient current the TVS can safely conduct. Higher ratings (SMA6J33A-TP at 11.3A) provide additional margin for larger transient events. For equivalent protection, 7.5A substitutes are directly compatible with the original SMAJ33 specification.

Q: Why do some parts have higher power ratings (600W vs. 400W)?

A: Power rating reflects the maximum energy dissipation during a 10/1000µs pulse. Higher ratings (SMA6J33A-TP at 600W) indicate enhanced thermal capability and are suitable for applications with larger or more frequent transient events. For equivalent protection, 400W substitutes match the original specification.

Q: Is packaging (Tape & Reel vs. Bulk) important for substitution?

A: Packaging affects supply chain logistics and production handling but does not impact electrical or mechanical compatibility. Tape & Reel packaging is standard for automated assembly; Bulk packaging is used for manual or lower-volume applications. Select based on your manufacturing process requirements.

Q: Are all substitutes RoHS compliant?

A: Yes, all listed substitutes are ROHS3 Compliant, meeting environmental and hazardous substance restrictions equivalent to the original SMAJ33.

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