Answer: The LM2596S-ADJ/NOPB is TI’s adjustable 3 A, 150 kHz buck regulator in the 5-pin surface-mount TO-263 (DDPAK). Feedback is 1.193–1.267 V at 25 °C, input is 4.5–40 V, and the switch drops 1.4 V max at 3 A. In this package the PCB copper is the heat sink: TI’s junction-to-ambient figure falls from 50 °C/W (0.5 in² single-sided) to 20 °C/W (3 in² double-sided). (TI SNVS124G §7.3, §7.4, §7.8, §7.9.)
Key specifications
| Parameter | Value | Condition | Source |
|---|---|---|---|
| Feedback voltage | 1.193 / 1.23 / 1.267 V; 1.18–1.28 V over temperature | VIN 4.5–40 V, ILOAD 0.2–3 A, VOUT set to 3 V | §7.8, p.6 |
| Input voltage | 4.5–40 V operating; 45 V abs. max | — | §7.3 and §7.1, p.5 |
| Switch saturation voltage | 1.16 typ / 1.4 max V; 1.5 V max over temperature | IOUT = 3 A | §7.9, p.7 |
| Max duty cycle | 100 % | Feedback forced to 0 V | §7.9, p.7 |
| Current limit (peak) | 3.6 / 4.5 / 6.9 A; 3.4–7.5 A over temperature | — | §7.9, p.7 |
| Oscillator frequency | 127 / 150 / 173 kHz; 110–173 kHz over temperature | — | §7.9, p.7 |
| Feedback bias current | 10 typ / 50 max nA; 100 nA max over temperature | VFB = 1.3 V | §7.9, p.7 |
| Quiescent current | 5 typ / 10 max mA | Switch forced off | §7.9, p.7 |
| Standby current | 80 typ / 200 max µA; 250 µA over temperature | ON/OFF = 5 V, VIN = 40 V | §7.9, p.7 |
| ON/OFF threshold | ON ≤ 0.6 V, OFF ≥ 2.0 V over temperature (1.3 V typ) | — | §7.9, p.7 |
| RθJA, TO-263 | 50 / 30 / 20 °C/W | 0.5 in² single-sided / 2.5 in² single-sided / 3 in² double-sided, 1-oz copper | §7.4 notes 5–7, pp.5–6 |
| Operating junction temperature | −40 to +125 °C | — | §7.3, p.5 |
| Moisture sensitivity | MSL 3, 245 °C peak, 168 h | LM2596S-ADJ/NOPB | Package Option Addendum |
Pinout (TO-263, 5 pins)
Table 6-1 (p.4): 1 VIN, 2 Output (switch), 3 Ground, 4 Feedback, 5 ON/OFF. It is the same order as the TO-220 version, so one schematic covers both. Keep the copper on pin 2 small: it is the switch node, and TI asks for minimum area there to limit coupling.
Setting the output
VOUT = 1.23 V × (1 + R2/R1), with R1 between 240 Ω and 1.5 kΩ (§9.2.2.2, p.28). With R1 = 1 kΩ (1 %):
| Target | R2 (E96) | Nominal VOUT |
|---|---|---|
| 3.3 V | 1.69 kΩ | 3.31 V |
| 5 V | 3.09 kΩ | 5.03 V |
| 12 V | 8.87 kΩ | 12.14 V |
The feedback window alone (1.193–1.267 V) gives about ±3 % at 25 °C and about ±4 % over temperature, before resistor tolerance. Above 10 V out, or with a very-low-ESR output capacitor, TI adds a feed-forward capacitor across R2 (§9.1.2, p.17).
Heat: the board is the heat sink
TI asks for at least 0.4 in² of copper under the tab, ideally 2 in² or more of 2-oz copper, and says gains are small beyond about 6 in² (§9.4.3, p.33). Its own TO-263 rise curve (Figure 9-19) is drawn at 2 A, and above 2 A it calls for double-sided or multilayer boards, large copper areas or airflow.
Worked example, 12 V to 5 V at 3 A (VSAT 1.16 V typ, diode drop 0.5 V as in TI’s design procedure):
- Duty cycle ≈ (5 + 0.5) / (12 − 1.16 + 0.5) = 0.485
- Switch conduction loss ≈ 1.16 V × 3 A × 0.485 = 1.69 W; with 5 mA × 12 V quiescent, about 1.75 W in the IC
- Junction rise: 88 °C at 50 °C/W, 53 °C at 30 °C/W, 35 °C at 20 °C/W
At 40 °C ambient that is 128 °C (over the limit), 93 °C, or 75 °C. So a 3 A design needs the large-copper or double-sided layout, not the 0.5 in² footprint. The catch diode and inductor heat the same copper, which these numbers leave out.
Design notes
- Catch diode. Rated at least 1.3 × the maximum load current (or the full current limit if the output must survive a short), with reverse voltage at least 1.25 × the maximum input. Use a Schottky; TI says 1N5400-series rectifiers are much too slow (§9.1.4, p.17; §9.2.2.2.5, p.30).
- Cold starts. TI does not recommend electrolytic capacitors below −25 °C, where ESR rises about 3× (10× at −40 °C); it suggests solid tantalum there (§9.1.3, p.17).
- ON/OFF pin. Tie it to ground or leave it open to run. It accepts up to 25 V for shutdown (Table 6-1, p.4).
Pitfalls specific to LM2596S-ADJ
- Skipping the bake. The DDPAK orderables are MSL 3 (168 h floor life at 245 °C), unlike the MSL 1 TO-220 versions. Reels opened for longer need baking before reflow.
- Trusting the 0.5 in² figure at 3 A. 50 °C/W with 1.75 W in the IC leaves no margin at 40 °C ambient.
- Flooding the switch pin with copper. Pin 2 should stay small; put the copper on the tab and ground.
- Using R1 above 1.5 kΩ to save current. TI’s range is 240 Ω–1.5 kΩ; larger values pick up noise on the feedback node.
Part numbers (information only)
| TI orderable | Package | Packing | MSL |
|---|---|---|---|
| LM2596S-ADJ/NOPB | DDPAK/TO-263 (KTT), 5 pins | Tube of 45 | Level 3, 245 °C, 168 h |
| LM2596SX-ADJ/NOPB | DDPAK/TO-263 (KTT), 5 pins | Reel of 500 | Level 3, 245 °C, 168 h |
Both are listed Active with marking “LM2596S” in the Package Option Addendum. The through-hole version is the LM2596T-ADJ.
FAQ
- What is the difference between LM2596S-ADJ and LM2596SX-ADJ? Only the packing: S is a tube of 45, SX is a reel of 500. Both are TO-263 (KTT) with the same die.
- How much copper does the TO-263 LM2596 need at 3 A? TI asks for at least 0.4 in² and ideally 2 in² or more of 2-oz copper. With about 1.75 W in the IC (12 V to 5 V), 30 °C/W or better keeps the junction near 93 °C at 40 °C ambient.
- What R1 should I use? TI recommends 240 Ω to 1.5 kΩ; 1 kΩ 1 % is the usual choice.
- What is the minimum input for 5 V out at 3 A? About 6.4 V at 25 °C and 6.5 V over temperature, from the 1.4 V and 1.5 V maximum saturation and 100 % duty cycle, ignoring inductor and trace drop.
- Does the ON/OFF pin need a pull-down? No. Left open or grounded, the regulator runs; drive it above 2.0 V to shut down.
Related (internal links)
- LM2596-ADJ calculator
- LM2596 equivalents: TI vs onsemi vs XL2596
- LM2596T-ADJ (TO-220)
- Power calculator
- Buck converters
- E-series resistors
Sources (retrieved 2026-10-26)
- Texas Instruments, LM2596 SIMPLE SWITCHER Power Converter 150-kHz 3-A Step-Down Voltage Regulator, SNVS124G (revised March 2023), including the Package Option Addendum: https://www.ti.com/lit/ds/symlink/lm2596.pdf
Disclaimer
Values are copied from TI SNVS124G and its Package Option Addendum, read on 26 Oct 2026; worked numbers are our arithmetic and ignore inductor, diode and trace losses. Verify against the current datasheet before production.
Reviewed by: Jasper · Updated: 2026-10-26