SMAJ28 Equivalent & Substitute Parts Reference

Part Overview

The SMAJ28 is a unidirectional transient voltage suppressor (TVS) diode manufactured by Littelfuse Inc., designed for general-purpose overvoltage protection in surface-mount applications. This component features a 28V reverse standoff voltage with a 47.67V maximum clamping voltage and 8.8A peak pulse current capability in a DO-214AC (SMA) package. The SMAJ28 is classified as obsolete, necessitating identification of active equivalent and substitute parts that maintain functional compatibility within specified electrical and mechanical parameters.

Key Parameters

Parameter	Value	Unit
Voltage - Reverse Standoff (Typ)	28	V
Voltage - Breakdown (Min)	29.48	V
Voltage - Clamping (Max) @ Ipp	47.67	V
Current - Peak Pulse (10/1000µs)	8.8	A
Power - Peak Pulse	400	W
Operating Temperature Range	-65 to 150	°C (TJ)
Package / Case	DO-214AC, SMA	—
Mounting Type	Surface Mount	—
RoHS Status	ROHS3 Compliant	—
Moisture Sensitivity Level	1 (Unlimited)	—

Substitute Part Grouping Explanation

Substitution of the SMAJ28 is determined by strict adherence to the following electrical and mechanical parameters:

Primary Substitution Criteria:

Voltage - Reverse Standoff: 28V (fixed requirement)
Voltage - Breakdown (Min): 29.48V to 31.1V (acceptable range)
Package / Case: DO-214AC, SMA (mechanical compatibility)
Mounting Type: Surface Mount (assembly compatibility)
RoHS Status: ROHS3 Compliant (regulatory requirement)
Moisture Sensitivity Level: 1 (Unlimited) (handling requirement)

Secondary Compatibility Parameters:

Voltage - Clamping (Max) @ Ipp: 45.4V to 51.6V (performance envelope)
Current - Peak Pulse: 8.8A to 68A (8/20µs) (protection capability)
Power - Peak Pulse: 400W to 4000W (thermal dissipation)
Operating Temperature Range: -50°C to -65°C minimum; 150°C to 175°C maximum (thermal operation)

Substitute parts are grouped into two categories based on clamping voltage performance:

Group A (Lower Clamping Voltage - 45.4V): SMAJ28A (MDD), SZ1SMA28AT3G (Littelfuse), SMAJ28A-13-F (Diodes Incorporated), SMAJ28A-TP (Micro Commercial Co), SMAJ28AE3/TR13 (Microchip Technology)

Group B (Higher Clamping Voltage - 51.6V to 59V): SMA6J28A-E3/5A (Vishay), SMA6J28A-E3/61 (Vishay), SMA6J28A-TR (STMicroelectronics), SMAJ28A-TR (STMicroelectronics)

Parameter Comparison

Part Number	Manufacturer	Product Status	Voltage - Reverse Standoff (V)	Voltage - Breakdown Min (V)	Voltage - Clamping Max @ Ipp (V)	Current - Peak Pulse (A)	Power - Peak Pulse (W)	Operating Temp (°C)	Package
SMAJ28	Littelfuse Inc.	Obsolete	28	29.48	47.67	8.8	400	-65 to 150	DO-214AC (SMA)
SMAJ28A	MDD	Active	28	31.1	45.4	8.8	400	-50 to 150	DO-214AC (SMA)
SZ1SMA28AT3G	Littelfuse Inc.	Active	28	31.1	45.4	8.8	400	-65 to 150	DO-214AC (SMA)
SMAJ28A-13-F	Diodes Incorporated	Active	28	31.1	45.4	8.8	400	-55 to 150	DO-214AC (SMA)
SMAJ28A-TP	Micro Commercial Co	Active	28	31.1	45.4	8.8	400	-55 to 175	DO-214AC (SMA)
SMAJ28AE3/TR13	Microchip Technology	Active	28	31.1	45.4	11	500	-65 to 150	DO-214AC (SMA)
SMA6J28A-E3/5A	Vishay General Semiconductor	Active	28	31.1	51.6	68 (8/20µs)	4000	-55 to 150	DO-214AC (SMA)
SMA6J28A-E3/61	Vishay General Semiconductor	Active	28	31.1	51.6	68 (8/20µs)	4000	-55 to 150	DO-214AC (SMA)
SMA6J28A-TR	STMicroelectronics	Active	28	31.1	51.6	68 (8/20µs)	600	-55 to 175	DO-214AC (SMA)
SMAJ28A-TR	STMicroelectronics	Active	28	31.1	59	39 (8/20µs)	400	-55 to 150	DO-214AC (SMA)

Engineering Selection Recommendations

Direct Replacement (Group A - Matched Clamping Voltage):

SZ1SMA28AT3G (Littelfuse Inc.) is the manufacturer-recommended direct replacement for the obsolete SMAJ28. This part maintains identical reverse standoff voltage (28V), equivalent clamping voltage (45.4V), and matching peak pulse current (8.8A) with active product status. The operating temperature range extends to -65°C minimum, matching the original specification. AEC-Q101 automotive qualification and REACH compliance provide enhanced reliability documentation.

SMAJ28A-TP (Micro Commercial Co) provides an alternative with extended upper operating temperature to 175°C and active inventory status. This part is suitable for applications requiring elevated temperature performance while maintaining all critical electrical parameters.

SMAJ28AE3/TR13 (Microchip Technology) offers increased peak pulse current (11A) and power dissipation (500W) within the same package and voltage class, providing enhanced protection margin for applications with higher transient stress.

Alternative Selection (Group B - Higher Clamping Voltage):

SMA6J28A-TR (STMicroelectronics) and SMA6J28A-E3/5A (Vishay) provide higher clamping voltage (51.6V) with significantly increased peak pulse current (68A at 8/20µs). These parts are suitable for applications requiring enhanced transient suppression capability. The higher clamping voltage represents a trade-off that may affect circuit performance in voltage-sensitive applications.

SMAJ28A-TR (STMicroelectronics) offers intermediate clamping voltage (59V) with moderate peak pulse current (39A at 8/20µs), providing a middle-ground option between Group A and higher-performance alternatives.

Compliance Considerations:

All substitute parts maintain ROHS3 compliance and MSL Level 1 (Unlimited) moisture sensitivity rating. Parts with AEC-Q101 qualification (SZ1SMA28AT3G) are suitable for automotive applications. REACH compliance status is documented for all active parts.

Frequently Asked Questions (FAQ)

Q: Can SMAJ28A (MDD) be used as a direct replacement for the obsolete SMAJ28?

A: SMAJ28A meets the core electrical requirements: 28V reverse standoff voltage, 45.4V clamping voltage, 8.8A peak pulse current, and DO-214AC (SMA) package compatibility. However, the minimum operating temperature is -50°C versus the original -65°C. Selection depends on application temperature requirements.

Q: What is the difference between Group A and Group B substitute parts?

A: Group A parts (45.4V clamping) maintain the original clamping voltage profile, ensuring circuit behavior consistency. Group B parts (51.6V to 59V clamping) provide higher voltage suppression with increased peak pulse current capability, suitable for applications requiring enhanced transient protection but may alter circuit voltage response characteristics.

Q: Is SZ1SMA28AT3G the recommended replacement?

A: SZ1SMA28AT3G is the manufacturer-recommended part from Littelfuse Inc., the original SMAJ28 manufacturer. It maintains all critical electrical parameters, extends the minimum operating temperature to -65°C, and includes AEC-Q101 automotive qualification.

Q: Can higher-current parts like SMA6J28A-TR be used in place of SMAJ28?

A: SMA6J28A-TR maintains the 28V reverse standoff voltage and DO-214AC (SMA) package compatibility but features higher clamping voltage (51.6V) and peak pulse current (68A at 8/20µs). This substitution is valid only if the application circuit can tolerate the higher clamping voltage without performance degradation.

Q: Are all substitute parts RoHS3 compliant?

A: All substitute parts listed are ROHS3 compliant and carry MSL Level 1 (Unlimited) moisture sensitivity rating, meeting current regulatory and handling requirements.

Q: What packaging options are available for substitute parts?

A: All substitute parts are supplied in DO-214AC (SMA) surface-mount package. Packaging formats include Cut Tape (CT), Digi-Reel®, and Tape & Reel (TR) options depending on the specific part number and manufacturer.

Q: Which substitute part has the widest operating temperature range?

A: SMAJ28A-TP (Micro Commercial Co) and SMA6J28A-TR (STMicroelectronics) both support -55°C to 175°C operating range, providing the widest upper temperature capability among active substitutes.

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