The onsemi LM2596 is an adjustable-output, nonsynchronous step-down switching regulator that converts a higher DC input into a lower regulated output. It operates from 4.5 V to 40 V and can supply loads up to 3 A when the inductor, catch diode, capacitors, PCB layout, and thermal design meet datasheet requirements. By switching energy through an inductor rather than dissipating excess voltage as heat, it can operate more efficiently than a linear regulator. This article covers its pinout, operation, specifications, 12 V-to-5 V design, efficiency, PCB layout, and load testing.

Catalog

Figure 1. LM2596

LM2596 Pinout and Packages

Figure 2. LM2596 Package Options and Pin Functions

The onsemi LM2596 uses a 5-pin configuration and is offered in TO-220 and D²PAK package families. The datasheet shows two TO-220 lead-form variants and one D²PAK surface-mount version.

LM2596 Package Options

These are onsemi-specific package names and case numbers. Other manufacturers may use different suffixes or package codes for electrically equivalent LM2596 devices.

LM2596 Pin Functions

For the onsemi LM2596, the same five electrical pin functions apply to the package versions shown. In adjustable versions, the Feedback pin connects to an external resistor divider that sets the output voltage.

Architecture & Working Principle

LM2596 Architecture

Figure 3. LM2596 Internal Block Diagram and Typical Buck Converter Application

The LM2596 is a nonsynchronous buck regulator that integrates the main control circuitry and a 3 A power switch in one IC. Its internal architecture includes a 1.235 V reference, error amplifier, comparator, 150 kHz oscillator, latch, switch driver, current-limit circuit, thermal shutdown, and ON/OFF control. The external inductor, catch diode, and output capacitor form the power-conversion and filtering stage. In the adjustable version, the feedback resistor network senses the output voltage and returns a scaled voltage to the feedback pin for regulation.

LM2596 Working Principle

During operation, the LM2596 repeatedly switches its internal power transistor at a nominal 150 kHz. When the switch turns on, current flows from the input through the switch and inductor to the load, storing energy in the inductor. When the switch turns off, the inductor keeps current flowing through the external catch diode. The output capacitor smooths the switching waveform and supplies the load between switching intervals. The feedback circuit continuously compares the sensed output with the internal reference and adjusts the switch duty cycle to maintain the required output voltage as input voltage or load changes. Under excessive current or temperature, the built-in current-limit and thermal-shutdown circuits protect the regulator; severe overload can also cause the switching frequency to decrease.

LM2596 Key Specifications

Designing a 12 V to 5 V onsemi LM2596 Circuit

Figure 4. LM2596 Adjustable 12 V to 5 V Typical Application Circuit

The adjustable LM2596 uses a feedback resistor divider to set the output voltage. The output-voltage equation is:

$$V_{\text{OUT}}=V_{\text{REF}}(1+\frac{R_2}{R_1})$$

where V_REF is approximately 1.23 V, R₁connects from the Feedback pin to ground, and R₂connects from the regulated output to the Feedback pin.

To calculate R_2for a required output voltage:

$$R_2=R_1(\frac{V_{\text{OUT}}}{V_{\text{REF}}}-1)$$

For a 5 V output with R₁ = 1.0" k" Ω:

$$R_2=1.0\text{kΩ}(\frac{5\text{V}}{1.23\text{V}}-1)\approx 3.07\text{kΩ}$$

Using the 3.1 kΩ resistor shown in the typical application circuit:

$$V_{\text{OUT}}=1.23\text{V}(1+\frac{3.1\text{kΩ}}{1.0\text{kΩ}})\approx 5.04\text{V}$$

Therefore, the 3.1 kΩ value produces an output close to the nominal 5 V target.

For an ideal buck converter, the approximate duty cycle is:

$$D\approx \frac{V_{\text{OUT}}}{V_{\text{IN}}}$$

For a 12 V input and 5 V output:

$$D\approx \frac{5\text{V}}{12\text{V}}\approx 0.417=41.7\text{\%}$$

This is an ideal estimate. The real duty cycle differs because of voltage drops across the internal switch, Schottky diode, inductor, and PCB connections.

At a 3 A output load, the output power is:

$$\begin{array}{c}{P}_{\text{OUT}}=V_{\text{OUT}}{I}_{\text{OUT}}\\ P_{\text{OUT}}=5\text{V}\times 3\text{A}=15\text{W}\end{array}$$

The 15 W value is output power, not the power dissipated by the LM2596. Continuous 3 A operation still depends on the inductor, diode, capacitors, PCB layout, cooling, and ambient temperature.

LM2596 Efficiency and Thermal Performance

Efficiency compares the DC power delivered to the load with the DC power drawn from the input:

$$\eta =\frac{P_{\text{OUT}}}{P_{\text{IN}}}\times 100\text{\%}=\frac{V_{\text{OUT}}{I}_{\text{OUT}}}{V_{\text{IN}}{I}_{\text{IN}}}\times 100\text{\%}$$

onsemi reports 73% typical efficiency for its LM2596 test circuit at V_IN = 12 V, V_OUT = 5 V, I_OUT = 3 A, and T_J = 25°C. At this operating point:

$$\begin{array}{c}{P}_{\text{OUT}}=5\text{V}\times 3\text{A}=15\text{W}\\ P_{\text{IN}}\approx \frac{15\text{W}}{0.73}\approx 20.55\text{W}\\ P_{\text{LOSS,total}}\approx 20.55\text{W}-15\text{W}\approx 5.55\text{W}\end{array}$$

The calculated 5.55 W is the total converter loss, not only the power dissipated inside the LM2596. It includes losses in the internal switch, Schottky diode, inductor, capacitors, and PCB connections. Because 73% is a typical measured value, the calculated input power and loss are approximate rather than guaranteed results.

onsemi provides the following simplified estimate for power dissipated inside the regulator:

$$\begin{array}{c}D\approx \frac{V_{\text{OUT}}}{V_{\text{IN}}}\\ P_{\text{IC}}\approx \left(V_{\text{IN}}{I}_Q\right)+(D\times I_{\text{OUT}}\times V_{\text{SAT}})\end{array}$$

The approximate steady-state junction temperature without a heatsink is:

$$T_J\approx T_A+P_{\text{IC}}\times R_{\theta \text{JA}}$$

Only the power dissipated inside the LM2596 should be used as PIC. Do not use the total converter loss of 5.55 W in the junction-temperature equation. Full-load operation may require a heatsink for the TO-220 package or sufficient PCB copper for the D²PAK package. Thermal shutdown and current limiting are fault-protection features and should not be used as normal operating controls.

LM2596 PCB Layout, Ripple, and EMI

PCB layout strongly affects LM2596 stability, output ripple, and electromagnetic interference. Place CIN, D1, L1, and COUT close to the regulator. Keep the high-current paths short and wide, but minimize the copper area connected to pin 2 because this switch node carries a fast-changing voltage.

For the fixed LM2596-5.0, route pin 4 FB directly to the regulated output after L1, preferably near the positive terminal of COUT. Keep this trace away from the switch node, diode, and inductor. Use a low-impedance ground path and avoid allowing high diode or capacitor currents to flow through the feedback ground connection.

The approximate peak-to-peak inductor ripple current is:

$${\Delta I}_L\approx \frac{V_{\text{OUT}}(V_{\text{IN}}-V_{\text{OUT}})}{V_{\text{IN}}L{f}_S}$$

For V_IN = 12 V, V_OUT = 5 V, L = 33 µH, and f_S = 150 kHz:

$${\Delta I}_L\approx 0.59\text{A peak-to-peak}$$

Output-voltage ripple is approximately:

$${\Delta V}_{\text{OUT}}\approx {\Delta I}_L\times \text{ESR}+\frac{{\Delta I}_L}{8f_S{C}_{\text{OUT}}}$$

Lower capacitor ESR generally reduces ripple, but the capacitor must remain within TI’s capacitance and ESR recommendations for stable operation. A closed-core or shielded inductor can also reduce magnetic-field coupling and radiated EMI.

Measure ripple directly across COUT with a short oscilloscope ground spring. A long probe ground lead can pick up switching noise and display ringing that is not actually present at the output. Component and layout guidance should follow the TI LM2596 datasheet.

Bare LM2596 IC vs LM2596 Module

The bare onsemi LM2596 is only the switching-regulator IC. It requires an external inductor, Schottky diode, capacitors, feedback resistors, and a properly designed PCB. An LM2596 module combines these parts on one board. Therefore, the onsemi IC’s 3 A rating does not prove that every module can continuously deliver 3 A.

Figure 5. Bare LM2596 IC vs LM2596 DC-DC Buck Converter Module

LM2596 Load Testing and Validation

Load testing confirms whether an LM2596 circuit or module can maintain 5 V continuously without excessive ripple, voltage drop, or overheating. The following is a recommended validation method and should not be presented as author-measured data unless the test was completed.

Required Test Equipment

Use an adjustable DC supply, electronic load or power resistors, digital multimeters, an oscilloscope, and thermocouples or a thermal camera. Record the instrument accuracy, ambient temperature, input voltage, component values, regulator package, and cooling conditions.

Measure voltage directly at the converter terminals. Thin test leads can introduce voltage drop and produce misleading results.

Incremental Load Test

Set the input to 12 V and confirm the output is approximately 5 V before connecting a heavy load. Increase the current gradually rather than applying 3 A immediately.

Allow the temperature to stabilize at each major load point. Stop the test if the output collapses, the regulator repeatedly enters current limit or thermal shutdown, or any component approaches its rated temperature.

Measured Case Study and Manufacturer Characterization

Bentoutou et al. (2023) built an LM2596 prototype to convert the PEDAGO-SAT educational nanosatellite’s four-cell lithium-ion bus, approximately 16.8 V, to 12 V. Their bench used a DC supply, electronic load, multimeter, oscilloscope, and current probe. The paper describes one prototype; replicate count was not reported. Tests covered approximately 0.7 A, 2.1 A, and 3.0 A. At 2.099 A, input and output were 16.72 V and 11.93 V; measured input and output powers were 28.52 W and 25.04 W, giving 88% efficiency. Voltage and current ripple were 244 mV and 60 mA. At 3.0 A, efficiency fell to 85%. Instrument accuracy, ambient temperature, test duration, and space-environment qualification were not reported. The result supports the 2.1 A laboratory requirement, not a universal LM2596 capability.

LM2596 vs LMR51430 vs MP1584

These regulators can deliver up to 3 A, but they differ in input range, switching method, package size, efficiency behavior, and lifecycle status.

Technical References

• onsemi. LM2596: 3.0 A, Step-Down Switching Regulator. Rev. 1, Publication Order No. LM2596/D, December 2022.

• onsemi. LM2596ADPBCKGEVB – LM2596 3 A Buck Demo Board Schematic. Rev. 1.0.

• onsemi. LM2596ADPBCKGEVB – LM2596 3 A Buck Demo Board Test Procedure. Rev. 1.0.

• onsemi. LM2596 Evaluation Board Bill of Materials. LM2596ADBCKGEVB.

• onsemi. TO-220 5-Lead Offset Mechanical Case Outline, Case 314B-05. Package Dimensions.

• onsemi. D²PAK 5-Lead Mechanical Case Outline, Case 936A-02. Package Dimensions.