NCV4266 Pinout Guide — 5V/150mA Automotive LDO with Enable | ICMASS

NCV4266 Pinout and Pin Functions

Typical Application Circuit

The 1Ω resistor with C_IN2 (100nF) prevents a failure mode that's hard to reproduce on a bench. Without it, the ceramic cap and wiring harness inductance form a high-Q LC tank. A load-dump or injector switching event excites that tank.

The resulting ringing at the NCV4266's input can exceed 45V even if the harness voltage stays within limits. The resistor costs a fraction of a cent.

For the EN pin: verify the GPIO high-level voltage meets 2.0V minimum across temperature. A 3.3V GPIO at -40°C might droop to 2.8V — still safe. A 1.8V GPIO won't reliably turn the regulator on. Use a level shifter or tie EN to IN with a 100kΩ pull-up.

PCB Layout Tips

• Solder the tab to a solid copper area — minimize thermal relief. The tab is the primary heat path out of the SOT-223. Thermal-relief spokes increase the thermal resistance between the tab and the copper plane. For a part dissipating 1W, every degree of thermal resistance matters. If your assembly process requires thermal relief for solderability, use the widest spokes your fab allows and connect to as large a copper area as possible.
• Place C_OUT within 5mm of Pin 4 and the GND tab. The output capacitor is part of the LDO's control loop. Trace inductance between the cap and the output pin adds phase shift that eats into phase margin. Every millimetre matters.
• Keep the input capacitors on the same side of the board as the IC. Vias add roughly 0.5–1nH each. At the frequencies where input ripple matters (100kHz–10MHz from the upstream DC-DC), via inductance degrades bypass effectiveness.
• Don't share the GND return path with high-current traces. If the NCV4266's GND pin shares a return path with a 5A motor driver, the voltage drop across the shared trace impedance appears as an offset on the output. Star-ground or use a solid plane.
• EN trace can be thin (6–8mil) and long. It's a high-impedance digital input. No current flows. Route it wherever it fits, but keep it away from switching nodes (inductor pads, MOSFET drains) to avoid capacitive coupling.

Frequently Asked Questions

Q1: Is the NCV4266 pin-compatible with a standard 3-pin SOT-223 LDO?

A: No. The NCV4266 has 4 pins with EN on Pin 3. Standard 3-pin parts have different assignments. On a 3-pin SOT-223 like the NCP1117, Pin 1 is GND, Pin 2 is OUT, Pin 3 is IN. The NCV4266 uses Pin 1=IN, Pin 2=GND, Pin 3=EN, Pin 4=OUT. These are not drop-in swaps — verify the footprint for each part before committing to a layout.

Q2: What happens if I leave the EN pin floating?

A: The output becomes unpredictable. The NCV4266 datasheet specifies the EN pin must be driven — internal pull-down may not be reliable across all conditions. Several LDOs in this class (including Intersil ISL78310 and others confirmed on TI E2E) explicitly state EN has no internal biasing. A floating EN in an automotive environment picks up noise from nearby switching nodes. The fix: tie EN to IN through a resistor, or drive it from a GPIO.

Q3: Can I connect EN directly to IN without a resistor?

A: Yes, it works, but a series resistor is cheap insurance. TI's E2E forum notes that hard-tying EN to V_IN can cause output overshoot during slow V_IN ramp-up. A 100kΩ resistor doesn't affect DC behaviour but lets you cut the trace for debugging. Some designs add a 10–100nF cap from EN to GND to delay enable until V_IN stabilises.

Q4: Why does the NCV4266 have 4 pins when most SOT-223 LDOs have 3?

A: The EN pin lets you shut down the output to <1µA via software. The 3-pin NCV4264 can't do that. If your ECU needs to kill the 5V rail in sleep mode, the NCV4266 does it with one GPIO. The NCV4264 needs an external load switch. On the flip side, the NCV4264's 3-pin layout is a drop-in for many legacy designs — pick based on whether you need shutdown control.

Q5: What's the minimum EN high voltage across temperature?

A: Per the onsemi NCV4266 datasheet (Rev 23): V_IH ≥ 2.0V minimum over -40°C to +150°C. At room temperature, typical threshold is lower (~1.5V). At cold, it rises toward the 2.0V spec limit. A 3.3V GPIO works with margin. A 1.8V GPIO doesn't guarantee turn-on at cold — use a level shifter. This is a common pitfall discussed across LDO EN pin threads on StackExchange: always check the threshold at the worst-case temperature, not at 25°C.

Q6: How much PCB copper does the NCV4266 actually need?

A: At 150mA/12V in (1.05W), 300–500mm² of 1oz copper keeps the junction safe. EEVblog discussions on SOT-223 thermal design report R_θJA of 104–140°C/W on a minimal pad, dropping to ~50–70°C/W with 500mm². At 1.05W, that's a 53–74°C rise — fine at 85°C ambient. SOT-223 doesn't need thermal relief spokes - it can't tombstone. Connect the tab directly to a copper pour.

Q7: Should I put thermal vias under the SOT-223 tab?

A: Yes, but place them around the pad perimeter, not under the solder joint. EEVblog manufacturing discussions warn that solder wicks down open vias during reflow, creating voids under the tab. Use 4–8 vias (0.3mm drill) on a ~1.27mm grid around the pad, connecting to an inner ground plane. Filled or plugged vias eliminate the wicking risk entirely.

Q8: Can the NCV4266 handle 45V input continuously?

A: Yes, but the thermal math limits you. 45V in, 5V out at 150mA = 6W — SOT-223 can't dissipate that. The 45V rating is a load-dump survivability spec. At 45V continuous, safe load is ~20–30mA before hitting thermal limits on typical PCB copper. Above 24V input, reduce load current or add a pre-regulator. The package's thermal limit, not the voltage rating, sets the real ceiling.

Related Products

• NCV4266-2CST50T3G — 5V/150mA Automotive LDO product page
• NCV4264-2CST33T3G — 3.3V/100mA Automotive LDO, 3-pin, no EN
• NCV4266 vs NCV4264 vs NCP1117 — Automotive vs Commercial LDO Selection Guide