SMBJ TVS Diodes: Package, Polarity and 24 V Rail Selection

An SMBJ TVS diode is a 600 W class part in a DO-214AA body, and the datasheet is unusually explicit about what that class includes: standoff voltages from.

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SMBJ TVS Diodes: Package, Polarity and 24 V Rail Selection

Updated: October 28, 2026

An SMBJ TVS diode is a 600 W class part in a DO-214AA body, and the datasheet is unusually explicit about what that class includes: standoff voltages from 5.0 V to 188 V, a bidirectional option marked by the CA suffix, moisture sensitivity level 1, and AEC-Q101 qualified ordering codes for automotive programmes. The 600 W figure belongs to a 10/1000 µs waveform with a duty cycle of 0.01 %, so the useful question is never “is 600 W enough” on its own — it is what the part clamps to at the current your event delivers.

What the Class Looks Like in a Real Datasheet

The features list on a TVS datasheet is a specification in disguise, so read it as one.

Vishay’s SMBJ series document 88392 describes the family from SMBJ5.0A through SMBJ188A: 600 W of peak pulse power capability on a 10/1000 µs waveform with a repetitive rate of 0.01 %, a low-profile glass-passivated chip junction, unidirectional and bidirectional availability, very fast response, and low incremental surge resistance. The mechanical notes add the SMB (DO-214AA) case, a moulding compound rated UL 94 V-0, moisture sensitivity level 1 per J-STD-020 with a 260 °C peak, and the three ordering families — E3 and M3 for commercial and halogen-free commercial grades, HE3 and HM3 for the AEC-Q101 qualified RoHS and halogen-free variants.

Parameter	Vishay SMBJ	STMicroelectronics SM6T (same class)
Peak pulse power	600 W at 10/1000 µs, duty cycle 0.01 %	600 W at 10/1000 µs, and 4 kW at 8/20 µs
Standoff voltage range	5.0 V to 188 V	5 V to 188 V
Polarity options	Unidirectional; CA suffix for bidirectional	Unidirectional; CA suffix for bidirectional
Leakage	Specified per part number at rated standoff	0.2 µA at 25 °C, 1 µA at 85 °C, with up to 350 W capability at a 150 °C junction
Package and mounting	SMB (DO-214AA), MSL 1, UL 94 V-0, 260 °C peak	SMB, MSL 1, JEDEC registered outline
Qualification options	HE3 and HM3 AEC-Q101 qualified variants	Standards coverage for IEC 61000-4-2 (30 kV air and contact) and IEC 61000-4-4 level 4

How to Select One, Step by Step

Work in this order and the part number usually selects itself.

Standoff first. Set the reverse standoff voltage above the highest normal voltage on the node, including tolerance and regulation. Below that threshold the device must not conduct.
Clamping second. Find the specified clamping voltage at the peak pulse current your event produces, and check it against the absolute maximum rating of the parts behind the diode. If clamping exceeds that, the protection has moved the failure rather than prevented it.
Energy third. Compare the pulse duration and energy of the real event with the 10/1000 µs, 0.01 % duty-cycle basis of the rating. Long, high-energy events belong to a different class of device.
Polarity fourth. Choose bidirectional with the CA suffix only when the node genuinely sees both polarities; on a DC rail, the unidirectional part’s forward path is usually useful behaviour.
Qualification and mechanics last. Confirm the automotive variant if the programme needs it, and the MSL and reflow conditions against the assembly process.

A Worked Selection for a 24 V Rail

The arithmetic is short, and it is the part of the job that prevents a return.

Suppose a 24 V nominal rail with tolerance to 28 V, and downstream electronics whose absolute maximum input is 40 V. The standoff requirement is above 28 V, which points at a 30 V class part in this family; the constraint that then matters is the clamping voltage at the peak pulse current the surge can deliver. If a specified 30 V part clamps at, say, 48 V at the rated pulse current, it does not protect a 40 V input — and the answer is either a lower-clamping device or a different protection architecture, not a bigger version of the same part.

This is a model with stated assumptions about the rail and the downstream limit, not a measurement, and the clamping figures must come from the datasheet of the exact part number rather than from the family summary. The point of the example is the order of the checks: standoff protects the TVS from the circuit, and clamping protects the circuit from the TVS.

Choose the SMBJ ordering code and suffix

Use this page for the SMBJ package, polarity suffix, and a concrete rail-selection review. Read standoff voltage, breakdown test current, clamping current, and the package outline from the same datasheet revision. The 600 W pulse-rating article owns the waveform and temperature-derating explanation.

Selection checklist before you freeze the MPN

Confirm working voltage (V_RWM) sits above the rail maximum including tolerance.
Match surge waveform and peak pulse power (P_PPM) to the threat—not only the catalog wattage label.
Check clamping voltage at the expected surge current against IC absolute-max ratings.
For high-speed lines, verify capacitance and whether unidirectional or bidirectional polarity fits the signal.
Re-check derating curves at your board temperature; catalog P_PPM is usually at 25 °C.

Ratings that decide real protection

Parameter	What to verify	Why it matters
V_RWM	Above max continuous voltage	Avoids leakage and false clamping in normal operation
V_C @ I_PP	Below protected IC abs-max	Clamping too high still destroys the load
P_PPM / waveform	8/20 µs vs 10/1000 µs as applicable	Watt labels are not interchangeable across pulses
C_j	Budget for USB/HDMI/RF integrity	Excess capacitance closes eyes on fast edges

FAQ

Unidirectional or bidirectional TVS—how do I choose?

Use unidirectional on DC rails with a defined polarity; use bidirectional on AC or reversible/signal lines where either polarity can appear.

Does a higher wattage TVS always protect better?

No. Clamping voltage, waveform rating, and layout often matter more than the wattage label alone.

Where should the TVS sit on the PCB?

At the entry connector with a short return to the surge ground—long stubs raise inductive overshoot.

SMAJ vs SMBJ vs SMCJ—what actually changes?

Mainly package size and peak pulse power capability; still match V_RWM, clamp, and waveform to the threat.

Official Resources

References

Vishay, SMBJ5.0A thru SMBJ188A — Surface-Mount TRANSZORB Transient Voltage Suppressors, document 88392 — source of the 600 W rise time basis with a 0.01 % duty cycle, the 5.0 V to 188 V standoff range, the CA suffix convention for bidirectional devices, the SMB (DO-214AA) case, UL 94 V-0 moulding compound, MSL 1 at 260 °C peak, and the E3/M3/HE3/HM3 ordering grades including AEC-Q101 qualified variants. vishay.com — SMBJ datasheet (PDF)
STMicroelectronics, SM6TxxA, SM6TxxCA — 600 W TVS in SMB — the same 600 W class from a second vendor, including the 4 kW (8/20 µs) rating, leakage of 0.2 µA at 25 °C and 1 µA at 85 °C, 350 W at a 150 °C junction, and IEC 61000-4-2 and IEC 61000-4-4 coverage. st.com — SM6T series datasheet (PDF)
Bourns, SMCJ Transient Voltage Suppressor Diode Series — the 1500 W class used for the package comparison, in the DO-214AB outline. bourns.com — SMCJ series datasheet (PDF)
Texas Instruments, Protection against Unsuppressed Load Dump in Automotive Systems, SNOAAA1 — pulse parameters used when checking whether a 600 W class part suits an automotive bus. ti.com — unsuppressed load dump application brief (PDF)

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