Pulse power is a package question: the SOD-123 package protects small lines with modest energy, and the SMB carries the 600 W class with a larger body and a better heat path. This guide compares the capability bands, the board-area trade, and the selection rules.
Pulse Power Is a Package Question
The TVS’s pulse-power capability is set by the die and the package together: the die absorbs the surge energy, and the package moves the heat away. A larger package body and a better thermal path let the same die class carry more pulse power, which is why the package is the second half of the TVS rating.
The selection reads the package with the waveform: the pulse-power number is quoted at a defined width, and the package’s capability at the application’s event is the comparison.
SOD-123 vs SMB Capability Comparison
| Package | Typical pulse-power class | Heat path | Typical line |
|---|---|---|---|
| SOD-123 | Low (sub-200 W class) | Small body, board solder | Small-signal and data lines |
| SMB (DO-214AA) | 600 W class | Larger body, better board contact | Power and automotive lines |
The table is the capability band: the SOD-123 serves the small lines where the surge is modest, and the SMB carries the power lines where the 600 W class is needed. The ASMBJ28CA is the SMB example—28 V, 600 W, automotive lighting-driver positioning.
Board Area vs Protection Level
The board-area trade follows the capability: the SOD-123’s small body saves space but protects less, and the SMB’s larger body costs space but carries the 600 W class. The product’s board budget and the line’s surge level are the two sides of the trade, read together at the actual event.
600 W SMB Examples in Automotive
The automotive lighting lines are the SMB’s home: the 28 V, 600 W class covers the 12 V rail’s transients, and the SMB package’s heat path carries the repeated pulse duty. The ASMBJ28CA is the cell of that class, and its clamping parameters are confirmed with the supplier before design-in.
The Board Is Part of the Package.
The pulse-power capability is read on the assembled board: the copper under the package, the vias, and the solder joint all move the junction temperature during the surge, so the package comparison is confirmed by a surge measurement at the actual layout before the part is locked.
Selection Rules of Thumb
- Read the event’s pulse power at the application’s width.
- Match the package band—SOD-123 for small lines, SMB for the 600 W class.
- Check the board area against the product’s budget.
- Place the TVS close to the entry with a short ground return.
- Confirm the clamping against the protected part’s limit.
The selection rules also read the placement and the layout: the TVS sits close to the entry with a short, wide ground return, and the clamp loop’s inductance is part of the protection. The package comparison and the placement are read together, because a 600 W SMB in the wrong place clamps late and protects less than a smaller part placed well. The rules close with the measurement: the clamp waveform at the actual surge, and the protected part’s margin, are the acceptance test for the package and the placement.
The package comparison also reads the production and the cost: the SOD-123’s smaller body and lower cost suit the high-volume small lines, and the SMB’s larger body and higher capability suit the power lines where the protection matters more than the board area. The comparison is a cost-versus-capability decision, read at the volume and the line’s surge level. The selection’s record—the event, the package, the placement, and the measurement—is the protection design’s evidence, and the field history reads it. The SMB versus SOD-123 choice is a package-and-placement decision, and the measurement is its judge.
The selection also reads the automotive lines’ reality: the 12 V rail’s transients, the lighting driver’s surge events, and the board’s space budget are the inputs, and the 600 W SMB class covers the lines where the events demand it. The ASMBJ28CA is the 28 V cell of that class, and its clamping and pulse-power curves are confirmed with the supplier. The package comparison and the placement are read together—a 600 W SMB in the wrong place clamps late—and the measurement on the prototype is the judge. The record—the event, the package, the placement, and the clamp—is the protection design’s evidence.
Engineering note. The package capability bands follow the TVS package structure and the pulse-power convention; the exact numbers come from the selected parts’ datasheets at the application’s pulse width.
The Automotive Lines in Practice
The automotive lighting lines are the SMB’s home: the 12 V rail’s transients, the driver’s surge events, and the board’s space budget are the inputs, and the 600 W class covers the lines where the events demand it. The ASMBJ28CA is the 28 V cell of that class, and its clamping and pulse-power curves are confirmed with the supplier. The package comparison and the placement are read together—a 600 W SMB in the wrong place clamps late—and the measurement on the prototype is the judge. The record—the event, the package, the placement, and the clamp—is the protection design’s evidence, and the selection rules close with it.
The Automotive Selection in Full.
The selection reads the automotive lines in full: the 12 V rail’s transients, the driver’s surge events, and the board’s space budget are the inputs, and the 600 W SMB class covers the lines where the events demand it. The ASMBJ28CA is the 28 V cell of that class, and its clamping and pulse-power curves are confirmed with the supplier. The package comparison and the placement are read together—a 600 W SMB in the wrong place clamps late—and the measurement on the prototype is the judge. The record—the event, the package, the placement, and the clamp—is the protection design’s evidence, and the selection rules close with it. The SOD-123 serves the small lines where the board area wins, and the two packages stay in their bands when the event and the board are read together.
The Package Decision in Full.
The SMB versus SOD-123 decision is read in full: the event’s pulse power at the width, the package band, the board area, and the placement are the four columns, and the measurement on the prototype closes them. The automotive lines demand the 600 W SMB class, and the ASMBJ28CA is the 28 V cell with the clamping confirmed. The SOD-123 serves the small lines where the board area wins, and the two packages stay in their bands when the event and the board are read together. The record—the event, the package, the placement, and the clamp—is the protection design’s evidence.
The Selection Record.
The selection’s record closes the design: the event’s waveform, the package band, the placement drawing, and the clamp measurement are filed together, and the protection design’s review reads the same record. The 600 W SMB class on the automotive lines and the SOD-123 on the small lines are the two bands, and the measurement on the prototype is the judge. The record is what the next protection design reads first, and the field history is its continuation. The package and the placement are one decision, and the record makes it repeatable.
The Selection Record.
Frequently Asked Questions
Why is pulse power a package question?
The die absorbs the energy and the package moves the heat; a larger body and a better thermal path carry more pulse power at the same die class.
What does SOD-123 protect?
Small lines with modest surge energy—the low-power class where the board area is the priority.
When do I need SMB?
On the power and automotive lines where the 600 W class is needed and the board can provide the space.
How do I select between them?
Read the event’s pulse power at the width, match the package band, check the board area, and confirm the clamping against the protected limit.
What is the ASMBJ28CA?
The 28 V, 600 W SMB TVS positioned for automotive lighting-driver lines, with the clamping parameters confirmed with the supplier.
Conclusion
The TVS package is the pulse-power contract: SOD-123 protects small lines cheaply, and SMB carries the 600 W class with the board area to match. Read the event, match the band, and place the clamp close to the entry.
Review the ASMBJ28CA product page on the Good-Ark site, and contact Good-Ark with your line’s surge level and board budget for a TVS package recommendation.