LM2596S-ADJ/NOPB vs LT1172CS8#PBF: Component Comparison for Practicing Hardware Engineers
Quick verdict
For straightforward 3A buck converter designs with input voltages up to 40V and minimal complexity, the LM2596S-ADJ/NOPB offers a simpler, higher current solution with a robust thermal package. For designs requiring versatility in topology (buck, boost, flyback, forward) or output polarity, or where input voltage can be as low as 3V, the LT1172CS8#PBF is the better choice despite its lower maximum current and more constrained thermal range.
Spec comparison table
| Spec | LM2596S-ADJ/NOPB | LT1172CS8#PBF | Notes |
|---|---|---|---|
| Function | Step-Down (Buck) | Step-Up, Step-Down, Step-Up/Step-Down, Cuk, Flyback, Forward | LT1172 supports multiple topologies, offering more flexibility. |
| Input Voltage Max | 40 V | 40 V | Equivalent; both can handle up to 40V input. |
| Input Voltage Min | 4.5 V | 3 V | LT1172 supports lower input voltage, useful for battery-powered or low-voltage inputs. |
| Mounting Type | Surface Mount | Surface Mount | Equal; both are SMD parts. |
| Number of Outputs | 1 | 1 | Equal. |
| Operating Temperature Range | -40°C to 125°C (TJ) | 0°C to 100°C (TJ) | LM2596S supports wider temperature range, better for industrial or harsh environments. |
| Output Configuration | Positive | Positive or Negative | LT1172 offers negative output option, useful in some specialized applications. |
| Output Current Max | 3 A | 1.25 A (Switch) | LM2596S can handle more than double the current, critical for higher load designs. |
| Output Type | Adjustable | Adjustable | Equal. |
| Output Voltage Max | 37 V | 65 V (Switch) | LT1172 supports nearly double max output voltage, important for high voltage rails. |
| Output Voltage Min | 1.2 V | 1.244 V | Similar; negligible difference. |
| Package Case | TO-263-6, D2PAK (5 Leads + Tab) | 8-SOIC (0.154”, 3.90mm Width) | LM2596S package better for thermal dissipation; LT1172’s SOIC is smaller but less robust thermally. |
| Supplier Device Package | TO-263 (DDPAK-5) | 8-SO | Same as above; thermal considerations favor LM2596S package. |
| Switching Frequency Typ | 150 kHz | 100 kHz | LM2596S’s higher frequency reduces external component size but can increase switching losses. |
| Synchronous Rectifier | No | No | Both use diode rectification, affecting efficiency and EMI. |
| Topology | Buck | Buck, Boost, Cuk, Flyback, Forward | LT1172 supports multiple converter types, increasing design flexibility. |
Design trade-offs
The LM2596S-ADJ/NOPB is optimized for simple buck conversion at currents up to 3A. Its 150kHz switching frequency allows for smaller inductors and capacitors compared to lower-frequency designs, but this comes at the expense of higher switching losses and potentially more EMI. The TO-263 package with a large exposed tab simplifies thermal management, allowing the device to dissipate heat more effectively during continuous high current operation. This makes it a strong candidate for power rails requiring up to 3A at moderate voltages (up to 37V output).
In contrast, the LT1172CS8#PBF supports multiple topologies beyond simple buck, including boost, flyback, and forward converters. This versatility comes at the cost of lower maximum output current (1.25A switch current rating) and a lower maximum junction temperature (100°C vs. 125°C), which restricts continuous power dissipation. The 100kHz switching frequency reduces switching losses relative to the LM2596S but requires larger magnetic components, increasing board space. The smaller 8-SOIC package is convenient for compact designs but requires careful PCB layout and thermal management to avoid overheating.
Neither device integrates a synchronous rectifier, so both require external Schottky diodes for efficient rectification, which impacts overall efficiency and heat dissipation. The LM2596S’s higher current capability means its diode must be rated accordingly, and thermal considerations for the diode become critical at higher load.
The LT1172’s ability to generate negative outputs and support a range of converter topologies provides an advantage in complex power systems where multiple rails or isolated supplies are needed. However, this flexibility is less relevant if the design is fixed to a single buck converter application. Additionally, the LT1172’s lower operating temperature range limits its use in industrial or automotive environments where ambient temperatures may exceed 85°C.
Cost-wise, the LM2596S is widely used and generally more cost-effective in volume due to its popularity and simplicity. The LT1172, offering more features, may command a higher price and necessitate more complex external components and design effort.
Use-case fit
Choose LM2596S-ADJ/NOPB when…
- Designing a single-output buck converter requiring up to 3A continuous load current.
- Operating in environments with high ambient temperatures or industrial temperature ranges (-40°C to 125°C).
- Minimizing thermal management complexity via a robust TO-263 package with an exposed tab.
- Needing a regulated output voltage down to 1.2V from inputs between 4.5V and 40V.
- Prioritizing lower component count and proven, mature design with widespread application notes.
Choose LT1172CS8#PBF when…
- The power supply design requires multiple topologies (buck, boost, flyback, forward) or negative output voltages.
- Input voltage can drop as low as 3V, such as in single-cell Li-ion battery-powered systems.
- Output current requirements do not exceed 1.25A, and the design can accommodate larger inductors due to the lower switching frequency.
- A compact 8-SOIC footprint is required and thermal dissipation can be managed within the 0°C to 100°C junction temperature range.
- Flexibility in converter architecture is needed for isolated or non-standard power rails.
Drop-in compatibility
These two devices are not pin- or footprint-compatible. The LM2596S-ADJ/NOPB uses a TO-263-6 (D2PAK with 5 leads + tab) package, while the LT1172CS8#PBF comes in an 8-lead SOIC package. Their pinouts, package sizes, and thermal characteristics differ significantly. Substituting one for the other requires a redesign of the PCB footprint and supporting components. Additionally, the LT1172 supports multiple topologies, so the surrounding components and layout will differ. There is no direct drop-in replacement scenario between these parts.
Alternatives to consider
- LM2675-ADJ (Texas Instruments): Lower current (1A) buck regulator with similar adjustable output and simple design—good for lower power applications.
- TPS5430 (Texas Instruments): 3A, synchronous buck converter with higher switching frequency and integrated synchronous rectifier for improved efficiency.
- LT1767 (Analog Devices): High frequency, synchronous buck regulator with integrated MOSFETs for up to 3A output, offering better efficiency at the cost of increased complexity.