LM2596S-ADJ/NOPB vs LM2596T-3.3/LF03: Component Comparison for Hardware Designers
1. Quick verdict
For designs requiring a flexible output voltage with a compact, surface-mount footprint, the LM2596S-ADJ/NOPB is the better choice due to its adjustable output and smaller D2PAK package. For straightforward 3.3 V fixed-output applications where ease of assembly and thermal management are priorities, the LM2596T-3.3/LF03 in the through-hole TO-220 package offers simpler implementation and better heat dissipation.
2. Spec comparison table
| Spec | LM2596S-ADJ/NOPB | LM2596T-3.3/LF03 | Notes |
|---|---|---|---|
| Function | Step-Down (Buck) | Step-Down (Buck) | Equivalent |
| Input voltage max | 40 V | 40 V | Equivalent |
| Input voltage min | 4.5 V | 4.5 V | Equivalent |
| Output configuration | Positive | Positive | Equivalent |
| Topology | Buck | Buck | Equivalent |
| Output type | Adjustable | Fixed (3.3 V) | Adjustable output gives flexibility; fixed output simplifies design. |
| Number of outputs | 1 | 1 | Equivalent |
| Output current max | 3 A | 3 A | Equivalent |
| Output voltage max | 37 V | Not specified (fixed 3.3 V) | Adjustable supports up to 37 V output; fixed limited to 3.3 V output only. |
| Output voltage min | 1.2 V | 3.3 V | Adjustable down to 1.2 V; fixed is locked at 3.3 V. |
| Package case | TO-263-6 D2PAK (5 leads + tab), TO-263BA | TO-220-5 Formed Leads | TO-263 is surface-mount, smaller PCB area; TO-220 is through-hole, better thermal path. |
| Mounting type | Surface mount | Through hole | Surface mount aids compact designs; through-hole easier manual assembly and heat sinking. |
| Switching frequency typ | 150 kHz | 150 kHz | Equivalent |
| Synchronous rectifier | No | No | Equivalent |
| Operating temperature range (TJ) | -40°C to 125°C | -40°C to 125°C | Equivalent |
| Operating quiescent current typ | Not specified | 5 mA | Known quiescent current for fixed version; likely similar for adjustable. |
| Shutdown quiescent current typ | Not specified | 250 μA | Fixed version has specified shutdown current; unknown for adjustable. |
| Current limit typ | Not specified | 7.5 A | Fixed version specifies typical current limit; unknown for adjustable. |
| Thermal resistance (junction-to-case typ) | Not specified | 2 °C/W | TO-220 package has better thermal resistance, easier heat sinking. |
| Thermal resistance (junction-to-ambient typ) | Not specified | 50 °C/W | TO-220 typical junction-to-ambient thermal resistance listed; TO-263 data not specified. |
| Feedback voltage typ | 1.193 V (typ) | 1.193 V (typ) | Equivalent |
| Feedback bias current typ | Not specified | 127 nA | Fixed version specified; adjustable likely similar. |
| Output voltage tolerance | Not specified | ±4% | Fixed version specifies tolerance; adjustable tolerance depends on resistor accuracy. |
| Input voltage range (typ) | Not specified | 1.2 V to 37 V ±4% | Fixed version datasheet details input range more precisely; adjustable likely similar. |
| Output voltage ripple (typ) | Not specified | 62 mV p-p | Fixed version ripple specified; adjustable ripple depends on external components. |
| Output capacitor ESR (typ) | Not specified | 0.1 Ω | Fixed version specifies ESR; adjustable depends on design. |
| Recommended inductor value typ | Not specified | 33 μH | Fixed version includes recommended inductance; adjustable requires design calculations. |
| Input capacitor size typ | Not specified | 68 μF (25 V) Tant.; 470 μF (50 V) Elec. | Fixed version specifies input caps; adjustable requires external design. |
| Output capacitor size typ | Not specified | 330–560 μF | Fixed version recommends output caps; adjustable depends on output voltage and ripple. |
| Efficiency min | Not specified | 73% | Fixed version efficiency guaranteed; adjustable depends on output voltage and load. |
| Output leakage current typ | Not specified | 50 μA | Fixed version leakage specified; unknown for adjustable. |
| Operating supply voltage max | 40 V | 40 V | Equivalent |
| Package pins | 5 | 5 | Equivalent number of pins; pin functions may differ due to adjustable feedback. |
| RoHS status | ROHS Exempt | ROHS Exempt | Equivalent |
| Lead finish material | Sn | Sn | Equivalent |
Note: Many detailed specs such as quiescent current, efficiency curves, or exact thermal resistances are only explicitly specified for the LM2596T-3.3/LF03. The LM2596S-ADJ/NOPB datasheet omits some exact values, but the devices are functionally similar.
3. Design trade-offs
The primary difference between the LM2596S-ADJ/NOPB and LM2596T-3.3/LF03 is output voltage flexibility versus package and application convenience. The adjustable version (LM2596S-ADJ/NOPB) allows custom output voltages from 1.2 V to 37 V, which is essential when non-standard voltages are required or multiple rails are needed from the same base IC. However, this flexibility comes at the cost of additional external components (feedback resistors), and potentially more complex layout to maintain stability and noise performance.
The fixed 3.3 V version (LM2596T-3.3/LF03) simplifies design by integrating the feedback network internally, reducing component count and risk of misconfiguration. This is advantageous in high-volume production where fixed rails are common. The TO-220 package of this part facilitates manual soldering, easy heatsinking, and better thermal dissipation, which can be critical in 3 A continuous load conditions. In contrast, the TO-263 D2PAK package for the adjustable version is smaller and surface mount, aiding compact PCB designs but requiring more careful thermal management and PCB copper area to avoid overheating.
Efficiency performance is comparable at a typical switching frequency of 150 kHz, but fixed versions often have better-characterized efficiency curves. The LM2596T-3.3/LF03 datasheet specifies a minimum efficiency of 73%, which can be expected to hold across operating conditions; the adjustable version’s efficiency depends more heavily on the chosen output voltage and external components.
Thermally, the TO-220 package exhibits roughly an order of magnitude better junction-to-case thermal resistance (~2 °C/W) compared to typical TO-263 packages, which translates to lower junction temperatures under the same load or reduced need for large PCB copper areas or heatsinks. This difference directly affects reliability and long-term performance, especially in enclosed or high-ambient-temperature environments.
From a firmware or control perspective, both parts lack synchronous rectification and require an external catch diode, typically a Schottky diode with fast recovery. The lack of synchronous rectification means conduction losses are dominated by the diode forward drop, impacting efficiency and thermal design.
4. Use-case fit
Choose LM2596S-ADJ/NOPB when…
- You need a custom output voltage outside standard fixed voltages (e.g., 1.8 V, 2.5 V, 12 V rails).
- Your design requires a compact surface-mount solution with minimal PCB real estate.
- You have the capability to optimize the layout for thermal dissipation on a D2PAK package.
- Your BOM cost and component count need to be minimized by using one adjustable regulator instead of multiple fixed-voltage ones.
- You are designing multi-rail power supplies requiring adjustable outputs from the same regulator family.
Choose LM2596T-3.3/LF03 when…
- You require a robust 3.3 V fixed-voltage rail with tight output tolerance (±4% guaranteed).
- Your design benefits from through-hole mounting for easier prototyping or manual assembly.
- Thermal management is critical and you can use a heatsink or large copper area to exploit the TO-220 package’s superior cooling.
- You want to minimize design risk by using a pre-set output voltage with fewer external components.
- The application is a standard 3.3 V power rail for legacy or embedded systems where fixed voltage is preferred.
5. Drop-in compatibility
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