The Rating on Page One Is a Ten-Second Number

Every one of these four datasheets carries the same footnote under its thermal characteristics: R_θJA measured on an FR4 board, t ≤ 10 sec.

That qualifier is doing a lot of work. A ten-second measurement is a transient thermal resistance — short enough that the heat hasn't yet spread out of the immediate copper under the die. A steady-state measurement lets the heat spread into the whole board, and the number gets substantially worse.

But why does a shorter measurement give a better number? Because a ten-second pulse only has to heat the copper directly under the die — and small areas heat fast, so the apparent thermal resistance looks low. Let the board soak and the real path is longer and far worse.

None of the four datasheets publishes a steady-state figure. Not one. The package power rating you see — 1.25W, 2.0W, 2.5W, 3.0W depending on part — is derived from that ten-second number.

So when a datasheet says 7A, it means 7A as long as the junction stays under 150°C, and the only published path to 150°C is the ten-second one.

Per Channel or Per Package? Read the Thermal Rows

This is where the four parts stop agreeing, and it changes your budget by a factor of two.

The NCE4606 splits its thermal rows per channel: it lists 62.5°C/W twice, once for the N-channel and once for the P-channel, and 2.0W against each. Read literally, that is 2.0W for each of the two channels.

The NCE4953 and NCE4963 each give one row — 50°C/W and 2.5W, 42°C/W and 3.0W. One number, not two. The NCE9926 gives one row as well at 1.25W and 100°C/W.

All four: FR4 board, t ≤ 10 sec, no steady-state figure published.

What about running both channels at once? For three of the four parts, that halves your per-channel budget — not a datasheet trick, just what one leadframe and one package can dissipate.

A practical consequence: if your design runs both channels hard at the same time, the part with the biggest single number is not necessarily the one with the most headroom per channel. The NCE4606 is the only part here whose two channels each get their own documented budget.

What Each Part Burns at Its Own Headline Current

Here is the number that decides everything: I²R at the printed current, against the printed budget.

Take each part at its own datasheet current and its own worst-case on-resistance at a realistic gate drive, and one channel tells the story.

Three of the four sit at 80% or more of their own budget with one channel conducting at the current printed on their own datasheets. And that 80%-plus figure is against a budget that only holds for ten seconds.

Notice too which parts land where. The two that run hottest are the ones with the least headroom per channel — and the NCE4953 reaches 94% not because its resistance is terrible but because its headline current is high relative to what a 2.5W package can shed.

Working Out a Continuous Current for Your Board

You don't need a thermal chamber. You need three numbers and one honest assumption.

Step one is where most designs go wrong, and it's the easiest to get right. Every one of these four parts publishes its resistance at a specific gate voltage, and picking the wrong row is a 60–70% error.

The NCE4953 goes from 55mΩ at −10V to 90mΩ at −4.5V. Use the row your driver actually produces.

Step two is the one people skip. Count the thermal rows. If the sheet gives one, both channels share it — and a design that switches two loads simultaneously has half the budget you thought.

Step three produces a number you should then distrust on purpose. The budget came from a ten-second measurement, so the honest move is to use a fraction of it and then verify by measuring the case temperature on a real board at real ambient.

Why the Low-Threshold Parts Are the Cool Ones

There is a real pattern across these four parts: the lower the gate drive they are characterized at, the lower their resistance and the better their thermal path — and the slower they switch.

The NCE4963 is characterized down to 2.5V and carries 42°C/W with a 3.0W package budget. The NCE4953 stops at 4.5V and carries 50°C/W with 2.5W. The NCE4606 publishes only 10V rows and splits 62.5°C/W per channel.

That is not coincidence. Part of the answer is silicon: these are different die generations aimed at different gate-drive markets, not bins of one design.

The cost shows up on the switching side. The NCE4963 has the lowest resistance here at 27mΩ at −4.5V — and also the largest input capacitance at 1210pF and the slowest turn-off at 70ns, roughly five times the NCE4953's 14ns.

A static switch gets that low resistance for free. A PWM stage pays for it in switching loss.

So the question is not which part is best. It is what your channel has to do.

When to Use a Dual SOP-8 — and When Not To

Use one when the switch is static or slow, the current is modest, and two channels in one footprint saves real board area. Load switching, battery disconnect paths, level-shifted high-side gates and low-frequency motor drive all fit. The dual package is genuinely the smallest way to get two 20–30V switches.

Don't use one when the load is inductive and unclamped. None of these four publishes an avalanche energy rating, and none publishes a body-diode recovery time. The unclamped edge at turn-off is an unquantified event on every part in the family.

Don't use one for steady current above an amp or two per channel. Both the thermal budget and the thermal path are board-limited, and the packages are small. A single TO-252 or TO-220 with a real heatsink carries more current with less arithmetic.

And don't use one if you need both polarities. Only the NCE4606 is complementary; the other three are duals of a single polarity, and the pin maps differ between them.

Internal Links

• NCE9926 — dual N-channel 20V SOP-8, 4.5V and 2.5V characterized
• NCE4606 — complementary N+P 30V SOP-8, with the full pin map
• NCE4953 — dual P-channel 30V SOP-8, 4.5V row published
• NCE4963 — dual P-channel 20V SOP-8, characterized to 2.5V

The Habit That Prevents All of This

Every mistake in this article comes from the same place: treating a printed number as a specification when it is actually a measurement condition.

From what we see across Shenzhen lots (2025–2026), the boards that come back are rarely built around the wrong part. They are built around the right part at the wrong drive voltage, or the right part at a current that only holds for ten seconds.

Three habits fix it. Read the resistance row that matches your gate drive, not the first one on the page.

Count the thermal rows to see whether your budget is per channel or per package. And when a sheet qualifies a number with a time limit, treat that number as a pulse rating no matter how the headline reads.

The datasheets are honest. All four of them tell you the conditions. The work is reading the conditions as carefully as the numbers.