LM2596T-ADJ/NOPB vs. LM2596S-12: A Practical Comparison
The LM2596 family remains a workhorse for simple, cost-sensitive buck conversions. For applications requiring a fixed 12V output, the LM2596S-12 offers a slightly more compact footprint and potentially easier initial implementation. However, if you need adjustable output voltage, the LM2596T-ADJ/NOPB is the only option, and its flexibility often outweighs the minor convenience of a fixed output.
Spec Comparison Table
| Spec | LM2596T-ADJ/NOPB | LM2596S-12 | Notes |
|---|---|---|---|
| Function | Step-Down | Step-Down | Identical |
| Output Configuration | Positive | Positive | Identical |
| Topology | Buck | Buck | Identical |
| Output Type | Adjustable | Fixed | Key difference: ADJ offers voltage programmability. |
| Number of Outputs | 1 | 1 | Identical |
| Input Voltage Min | 4.5V | - | LM2596S-12 datasheet lacks this spec. |
| Input Voltage Max | 40V | 40V | Identical |
| Output Voltage Min | 1.2V | 12V | LM2596T-ADJ allows for significantly lower outputs. |
| Output Voltage Max | 37V | - | LM2596T-ADJ allows for significantly higher outputs. |
| Output Current Max | 3A | 3A | Identical |
| Switching Frequency Typ | 150kHz | 150kHz | Identical |
| Synchronous Rectifier | No | No | Identical |
| Operating Temperature Range | -40°C ~ 125°C (TJ) | -40°C ~ 125°C (TA) | TA (ambient) for LM2596S-12 means less thermal margin; TJ (junction) for LM2596T-ADJ is preferable. |
| Mounting Type | Through Hole | Surface Mount | Significant difference impacting PCB layout and assembly. |
| Package Case | TO-220-5 Formed Leads | TO-263-6, D2PAK (5 Leads + Tab), TO-263BA | Footprint and pinout are not compatible. |
| Supplier Device Package | TO-220-5 | TO-263-5L | Reinforces package incompatibility. |
Design Trade-offs
The most significant difference lies in the package type. The LM2596T-ADJ/NOPB’s TO-220 package is through-hole, which simplifies prototyping and can be advantageous for low-volume production. However, it requires more board space and can be less thermally efficient compared to the LM2596S-12’s surface mount options (D2PAK, TO-263). The surface mount package of the LM2596S-12 enables denser PCB layouts and potentially better heat dissipation, but necessitates automated assembly.
Thermal considerations are important. While both parts have the same TJ rating, the LM2596T-ADJ’s TO-220 package generally requires more attention to heatsinking, especially at higher output currents and input voltages. The LM2596S-12’s surface mount packages offer better contact with the PCB, acting as a rudimentary heatsink.
Gate drive requirements are identical for both parts, as they both use an external N-channel MOSFET. However, the surface mount package of the LM2596S-12 can lead to slightly lower parasitic inductance in the gate drive loop, potentially reducing EMI.
Layout sensitivity is typical for this class of regulator. Both require careful attention to ground plane continuity and minimizing loop areas. The through-hole nature of the LM2596T-ADJ can sometimes make layout easier, but requires careful attention to lead length.
Cost at volume is likely to be similar, although the LM2596S-12’s surface mount package may slightly reduce assembly costs.
Use-Case Fit
Choose LM2596T-ADJ/NOPB when…
- You need adjustable output voltage: This is the primary reason to select this part. For example, in a system where the load voltage needs to be dynamically adjusted based on battery voltage or system requirements.
- Prototyping is a priority: The through-hole package simplifies breadboarding and initial testing.
- Low-volume production is expected: Manual assembly is more cost-effective for small quantities.
- Board space is not a primary constraint: The TO-220 package occupies more area compared to surface mount options.
- You are working with an existing design using a TO-220 package: Substituting a different package requires significant board rework.
Choose LM2596S-12 when…
- A fixed 12V output is sufficient: This simplifies the design and eliminates the need for external resistors.
- High-density PCB layouts are required: The surface mount package allows for a more compact design.
- Automated assembly is available: Surface mount components are essential for automated production.
- Improved thermal performance is desired: The surface mount package facilitates better heat dissipation.
- You’re designing a power supply for a consumer product with strict size constraints.
Drop-in Compatibility
These parts are not pin-compatible nor footprint-compatible. The TO-220 package of the LM2596T-ADJ/NOPB is fundamentally different from the surface mount packages (D2PAK, TO-263) of the LM2596S-12. Substituting one for the other requires a complete redesign of the PCB layout and a change in assembly process. The pinout is also different, requiring modification of the external circuitry.
Alternatives to Consider
- LM2596S-ADJ: Similar to the LM2596T-ADJ but in a surface mount package. Provides adjustable output voltage with a more compact footprint.
- LM2576: A slightly lower-cost alternative with similar functionality, but with lower current capability (3A max).
- TPS5430: A synchronous buck regulator offering higher efficiency and potentially smaller size, but at a higher cost and increased design complexity.
Power Electronics Digest
New references, design guides, and component updates — free.