LM2596S-5.0/NOPB vs LT1172CS8#PBF: Component Comparison for Power Electronics Design
Quick verdict
For straightforward, high-current, fixed 5 V step-down supplies with minimal design complexity, the LM2596S-5.0/NOPB is the better choice due to its higher maximum current (3 A) and simpler fixed output voltage. For flexible, multi-topology applications requiring adjustable output voltages, including boost or flyback configurations, the LT1172CS8#PBF is superior, offering broader topology support and adjustable output but limited to 1.25 A switch current.
Spec comparison table
| Spec | LM2596S-5.0/NOPB | LT1172CS8#PBF | Notes |
|---|---|---|---|
| Function | Step-Down (Buck) | Step-Up, Step-Down, Cuk, Flyback, Forward | LT1172 offers wider topology flexibility, enabling more design options. |
| Input Voltage Max | 40 V | 40 V | Equal max input voltage rating. |
| Input Voltage Min | 4.5 V | 3 V | LT1172 supports lower input voltage, useful for low-voltage or battery-powered designs. |
| Mounting Type | Surface Mount | Surface Mount | Equal. |
| Number of Outputs | 1 | 1 | Equal. |
| Operating Temperature Range | -40°C to 125°C (TJ) | 0°C to 100°C (TJ) | LM2596 supports wider temperature, improving reliability in harsher environments. |
| Output Configuration | Positive | Positive or Negative | LT1172 supports negative outputs, enabling more circuit topologies. |
| Output Current Max | 3 A | 1.25 A (Switch) | LM2596 handles more than twice the output current, suitable for higher-power loads. |
| Output Type | Fixed (5 V) | Adjustable (1.244 V minimum) | LT1172 allows custom output voltages for flexible design requirements. |
| Output Voltage Max | Not specified | 65 V (Switch) | LT1172 supports much higher output voltages, important for boost or flyback designs. |
| Output Voltage Min | 5 V | 1.244 V | LT1172’s adjustable output enables lower voltages than LM2596’s fixed 5 V. |
| Package Case | TO-263-6, D2PAK (5 leads + tab) | 8-SOIC (0.154”, 3.90 mm width) | LM2596’s larger package supports higher currents and thermal dissipation. |
| Supplier Device Package | TO-263 (DDPAK-5) | 8-SO | Smaller SOIC package for LT1172 reduces PCB space but limits power dissipation. |
| Switching Frequency Typ | 150 kHz | 100 kHz | Higher frequency for LM2596 reduces passive component size but may increase switching losses. |
| Synchronous Rectifier | No | No | Both use diode rectification, impacting efficiency and requiring external Schottky diodes. |
| Topology | Buck | Buck, Boost, Cuk, Flyback, Forward | LT1172’s multi-topology support enables more power conversion scenarios. |
Design trade-offs
The LM2596S-5.0/NOPB is optimized for simple buck conversion with a fixed 5 V output at currents up to 3 A. Its TO-263 package provides a large thermal pad and leads for effective heat dissipation, critical when operating near maximum current or in higher ambient temperatures (up to 125°C junction). The 150 kHz switching frequency balances passive component size and efficiency, but designers must account for potential EMI and switching losses at this frequency. The fixed output voltage simplifies layout and reduces external component count, but limits flexibility.
By contrast, the LT1172CS8#PBF targets broader applications requiring adjustable voltage and multiple topologies (buck, boost, flyback, forward, Cuk). Its maximum switch current of 1.25 A restricts output power compared to the LM2596, and the smaller 8-SOIC package limits thermal dissipation, requiring careful layout to avoid overheating, especially since the maximum junction temperature tops at 100°C. The lower switching frequency (100 kHz) eases EMI filtering and reduces switching losses but increases passive component size. The adjustable output and support for positive or negative outputs increase design complexity, requiring more external components and careful compensation, but enable applications such as isolated or negative rail generation.
Neither device integrates synchronous rectification, so both require external Schottky diodes for the freewheeling path, which impacts efficiency—especially at higher currents for the LM2596. Gate drive requirements are modest for both, but the LM2596’s internal power MOSFET and D2PAK package simplify driving and thermal management at 3 A loads. The LT1172’s lower current rating and smaller package reduce cost and PCB area but necessitate more careful thermal and layout design to maintain reliability.
Cost-wise, the LM2596 is a mature, widely used device with low cost in volume and extensive design resources. The LT1172, being more flexible and older analog topology, may have comparable or slightly higher cost per unit but adds design complexity that can increase overall development time and BOM cost.
Use-case fit
Choose LM2596S-5.0/NOPB when…
- You need a fixed 5 V output from an input voltage range of 4.5 V to 40 V.
- Your load current requirement is up to 3 A continuous.
- Operating environment includes wide temperature range, up to 125°C junction.
- You want a simple, proven buck converter with minimal external components.
- PCB space is not severely constrained and thermal dissipation is a priority.
Choose LT1172CS8#PBF when…
- Your application requires adjustable output voltage down to 1.244 V or up to 65 V.
- You need to implement boost, flyback, or forward converter topologies, not just buck.
- Input voltage can be as low as 3 V, such as in battery-powered or low-voltage rail scenarios.
- You need to generate a negative output rail or more complex power supply configurations.
- Your load current requirement is below 1.25 A and you can manage tighter thermal constraints.
Drop-in compatibility
These two devices are neither pin-compatible nor footprint-compatible. The LM2596S-5.0/NOPB uses a TO-263-6 (D2PAK-5) package with 5 leads plus a tab, optimized for high current and thermal dissipation, while the LT1172CS8#PBF is in an 8-pin SOIC package. Their pin functions and package outlines differ significantly, so substituting one for the other requires a full redesign of the PCB footprint, component placement, and possibly external components due to differing topologies and operating modes. No direct drop-in substitution is possible.
Alternatives to consider
- LM2675 (Texas Instruments): A fixed output, 1 A buck regulator with a simple design, smaller footprint, and lower current capability than LM2596, suitable for moderate current fixed voltage needs.
- LT1376 (Analog Devices): A 1.5 A step-down switching regulator with adjustable output and higher switching frequency (up to 300 kHz), offering a middle ground between LM2596 and LT1172 flexibility.
- MC34063 (ON Semiconductor): A classic adjustable switching regulator for low current (up to 1.5 A) with boost, buck, and inverting capabilities, useful for cost-sensitive designs requiring multiple topologies but lower efficiency.