LM2596S-ADJ/NOPB vs LM2596S-3.3-EV: Component Comparison for Power Electronics Engineers
1. Quick verdict
For designs requiring a flexible output voltage, the LM2596S-ADJ/NOPB is the clear choice due to its adjustable output range from 1.2V to 37V and robust maximum input voltage of 40V. Conversely, if your design demands a fixed 3.3V rail with minimal external components and typical loads up to 3A, the LM2596S-3.3-EV offers a straightforward solution with a fixed output and slightly simplified BOM, though note the more constrained input voltage max around 25V in some datasheet references.
2. Spec comparison table
| Spec | LM2596S-ADJ/NOPB | LM2596S-3.3-EV | Notes |
|---|---|---|---|
| Function | Step-Down Buck Regulator | Step-Down Buck Regulator | Equivalent function; no difference in topology. |
| Input Voltage Max | 40 V | 25 V (max per datasheet), up to 40V nominal | LM2596S-ADJ/NOPB allows higher input voltage margin. Important for 24V+ rails. |
| Input Voltage Min | 4.5 V | Not explicitly specified, typically ≥4.5V | LM2596S-ADJ/NOPB explicitly supports low voltage start. |
| Output Configuration | Positive | Positive | Equivalent. |
| Output Type | Adjustable (1.2V to 37V) | Fixed 3.3V | Adjustable output adds design flexibility; fixed output simplifies design and reduces external parts. |
| Number of Outputs | 1 | 1 | Equivalent. |
| Output Current Max | 3 A | 3 A (typ), 4.5 A max (per some notes) | LM2596S-3.3-EV datasheet notes up to 4.5A peak, but typical continuous rating is 3A; verify in application. |
| Output Voltage Max | 37 V | Fixed 3.3 V | Adjustable version covers a wider voltage range. |
| Output Voltage Min | 1.2 V | Fixed 3.3 V | Adjustable version supports lower voltages. |
| Package Case | TO-263-6 (D2PAK, 5 leads + tab) | TO-263-6 (D2PAK, 5 leads + tab) | Equivalent package type; footprint likely compatible. |
| Mounting Type | Surface Mount | Surface Mount | Equivalent. |
| Switching Frequency (typical) | 150 kHz | 25 kHz (typ) / 150 kHz (typ) conflicting data | LM2596S-ADJ/NOPB is consistently 150kHz; LM2596S-3.3-EV documentation shows 25kHz in some sources but elsewhere 150kHz; verify for your revision. |
| Synchronous Rectifier | No | No | Both use diode rectification; expect similar efficiency characteristics. |
| Operating Temperature Range | -40°C to 125°C (TJ) | -40°C to 125°C (TJ) | Equivalent. |
| Shutdown Current (typical) | Not specified | 80 µA | LM2596S-3.3-EV offers low shutdown current, beneficial for power-sensitive designs. |
| Input Current (typical) | Not specified | 80 µA | LM2596S-3.3-EV shows low quiescent current on input. |
| Input Current Max | Not specified | 4.5 A | LM2596S-3.3-EV can handle higher input current surge, useful in some transient scenarios. |
| Inductor Value (typical) | Not specified | 33 µH / 68 µH (conflicting) | LM2596S-3.3-EV typical designs specify 33µH or 68µH inductors; check design notes. |
| Output Capacitor | Not specified | 820 µF / 35 V | LM2596S-3.3-EV datasheet provides detailed external component guidance, easing design. |
| Input Capacitor | Not specified | 470 µF / 4 V | LM2596S-3.3-EV datasheet specifies input capacitor values, critical for stability. |
| Output Current Load Max (over line and load) | Not specified | +4% max | LM2596S-3.3-EV provides tighter output voltage regulation under varying load conditions. |
| Package Dimension | TO-263-6 (D2PAK-5L) | TO-220B-5L | Slight package variation; check footprint compatibility. |
| Output Voltage Ripple | Not specified | Not specified | No direct data; expect similar ripple given similar topology and frequency. |
3. Design trade-offs
The LM2596S-ADJ/NOPB excels in flexibility due to its adjustable output voltage range from 1.2V to 37V, making it suitable for varied rail requirements without changing the IC. This flexibility comes at the cost of requiring an external resistor divider for output voltage setting, increasing BOM count and layout complexity. Careful resistor selection is necessary to maintain output voltage accuracy and minimize noise coupling.
In contrast, the LM2596S-3.3-EV is a fixed 3.3V device, which simplifies the design by eliminating the need for external feedback resistors. This reduces PCB area and potential error sources in the voltage setting network. However, the fixed output limits the device to applications specifically requiring 3.3V, restricting its versatility.
Thermally, both devices share similar maximum junction temperatures (-40°C to 125°C) and packages (TO-263), implying comparable heat dissipation capabilities. However, the LM2596S-ADJ/NOPB’s wider input voltage range up to 40V allows it to handle higher input voltages, which can increase dissipation depending on input-output voltage differential. Designers must consider thermal derating and possibly larger heat sinking for higher voltage drops.
Switching frequency data for the adjustable device is consistent at 150kHz, favoring smaller inductors and capacitors for the same output ripple, but the LM2596S-3.3-EV has conflicting frequencies reported (25kHz and 150kHz). If the 25kHz figure applies, expect larger, more expensive inductors and capacitors, impacting cost and size. Verify your specific datasheet revision to confirm switching frequency.
Neither device includes synchronous rectification, so both rely on an external Schottky diode, which impacts efficiency and thermal management. Efficiency curves will be similar, but the fixed output device’s optimized internal compensation might give it slightly better regulation and transient response at 3.3V.
From a cost perspective, the adjustable device may be marginally more expensive due to additional internal circuitry for feedback and error amplification, but this is offset by the flexibility it offers. The fixed device’s simplified design can reduce overall system cost when only a 3.3V output is needed.
4. Use-case fit
Choose LM2596S-ADJ/NOPB when…
- You need to generate multiple different output voltages from the same regulator family without redesigning the board.
- Your input voltage rail can be as high as 40V, such as in automotive or industrial 24V nominal systems.
- Your design requires output voltages below 3.3V (down to 1.2V), for example, powering low-voltage digital ICs or FPGAs.
- You want to fine-tune the output voltage precisely via external resistor selection.
- The application involves prototyping or products that might require output voltage changes in later revisions.
Choose LM2596S-3.3-EV when…
- You require a fixed 3.3V output with minimal external component count.
- Your input voltage is stable and does not exceed 25V (or verify based on data sheet versions).
- Low quiescent current (shutdown current ~80µA) is important for battery-powered or low-power standby modes.
- You want tighter load and line regulation for a 3.3V rail (+/-4% max variation).
- Your design favors simplicity and potentially reduced PCB area by removing the adjustable feedback network.
5. Drop-in compatibility
Both devices share the TO-263-6 package with 5 leads plus a tab, which suggests footprint compatibility. However, the internal pinout, feedback pin functions, and package dimensions may differ slightly (TO-263BA vs TO-220B-5L noted in some datasheets), so direct substitution without schematic and layout verification is not guaranteed. The adjustable version requires external feedback resistors connected to the adjustment pin, absent in the fixed 3.3V version, which may have the feedback internally connected. Therefore, simply swapping these parts without adjusting the PCB or BOM can lead to incorrect output voltage or non-functional regulation.
In summary, these are not guaranteed drop-in replacements; careful evaluation of pin functions and PCB layout is necessary before substitution.
6. Alternatives to consider
- LM2596-5.0 (Texas Instruments): Fixed 5