Key Specs
| Spec | Value | Condition | Source |
|---|---|---|---|
| function | Step-Down | 🔵 api | |
| output_configuration | Positive | 🔵 api | |
| topology | Buck | 🔵 api | |
| output_type | Adjustable | 🔵 api | |
| number_of_outputs | 1 | 🔵 api | |
| input_voltage_min | 4.5V | 🔵 api | |
| input_voltage_max | 40V | 🔵 api | |
| output_voltage_min | 1.2V | 🔵 api | |
| output_voltage_max | 37V | 🔵 api | |
| output_current_max | 3A | 🔵 api | |
| switching_frequency_typ | 150kHz | 🔵 api | |
| synchronous_rectifier | No | 🔵 api | |
| operating_temperature_range | -40°C ~ 125°C (TJ) | 🔵 api | |
| mounting_type | Surface Mount | 🔵 api | |
| package_case | TO-263-6, D2PAK (5 Leads + Tab), TO-263BA | 🔵 api | |
| supplier_device_package | TO-263 (DDPAK-5) | 🔵 api |
When To Use
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24V industrial/24V bus → 16.0V @ 3A: The LM2596S-ADJ/NOPB supports input voltages up to 40V and delivers up to 3A continuous output current, perfectly matching a 24V bus stepping down to 16V at full load. Choosing a part with a lower maximum current rating risks thermal runaway under continuous 3A load, while a synchronous buck controller would add complexity and cost without necessary efficiency gains at this load and voltage range.
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12V automotive/battery rail → 5.0V @ 1.5A: This device’s 4.5V minimum input rating covers a cold or discharged 12V battery, and 3A max current rating provides ample margin for the 1.5A output. Using a part with synchronous rectification at this current might be overkill; conversely, a linear regulator would dissipate nearly 10W ((12−5)×1.5), causing immediate thermal shutdown.
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4.5V–40V wide-input supply → 1.2V–16.0V @ 2.2A: The wide input voltage range and adjustable output down to 1.2V make the LM2596S-ADJ/NOPB suitable for variable input rails with low-voltage loads up to 3A. A device limited to fixed output voltages or lower input voltage rating would either fail to regulate or suffer from shoot-through or latch-up under these conditions.
When Not To Use
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High-efficiency 3A buck design: The LM2596S-ADJ/NOPB does not include synchronous rectification, which raises conduction losses on the catch diode. Use a synchronous buck controller to reduce diode losses and improve efficiency.
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Output current above 3A continuous: The part’s maximum output current is 3A, which limits load capability. For loads exceeding this, select a multi-phase buck controller to share current across phases and prevent thermal runaway.
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Input to output voltage differential under 1V: The dropout voltage and switching topology make the LM2596S-ADJ/NOPB unsuitable for low dropout noise-sensitive applications. Use an LDO regulator for low noise and stable regulation at small voltage differentials.
Application Notes
IC dissipates ≈6.3W at Vin=40V→Vout=19.1V @ 1.5A (η≈82%). θJA = 50°C/W (TO-220, no heatsink, per datasheet). At 25°C ambient: TJ = 25 + 6.3×50 = 340°C — EXCEEDS the 125°C maximum. Heatsink is mandatory at full load. With a small heatsink (θJA ≈ 20°C/W): TJ ≈ 151°C.
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The switching node (SW) pin must be routed with a short, low-inductance copper path to minimize switching noise and voltage spikes; keep loop area small around SW, input, and ground pins.
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the Feedback pin and the Ground pin are noise-sensitive and should be routed away from the SW node to reduce feedback loop interference and maintain stable output voltage regulation.
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The output (switch) pin should not have large copper pours connected to it, as excessive copper can increase switching node capacitance and cause instability or increased EMI.
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Use a multilayer PCB with ground and power planes to distribute heat and reduce parasitic inductances; airflow or forced cooling may be required at load currents near 3A, especially at high input voltages.
Minimum External Components
Catch diode — Schottky, Vr ≥ 40V, If ≥ 3A Selection: Schottky forward recovery < 10ns vs 200–500ns for silicon. At 150kHz (period = 6.7µs), a 500ns-recovery diode is off for only 6.2µs before the next switch-on — it never fully turns off. Failure mode: Standard silicon rectifier: 200–500ns reverse recovery at 150kHz causes shoot-through current spikes every cycle — IC switch current exceeds rating, causing thermal runaway or immediate failure.
Output inductor — 68µH Selection: Isat ≥ 3.8A (peak current at max load). DCR < 100mΩ to limit conduction loss. At Vin=22V→Vout=5.5V: range is 33–68µH (30%→15% current ripple). Use 68µH for good regulation; 33µH acceptable if BOM cost is critical. Isat must be ≥ 3.8A — under-sizing Isat is the leading cause of field failures: the inductor saturates under peak current, spiking IC switch current beyond its rating. Failure mode: Isat below peak inductor current → core saturates → effective inductance collapses → switch current spikes beyond IC rating → thermal shutdown or permanent failure.
Input capacitor — ≥100µF electrolytic + 100nF ceramic (parallel) Selection: Electrolytic handles bulk ripple current; ceramic bypasses switching spikes. Voltage rating ≥ 40V with 20% margin. Failure mode: Insufficient input capacitance: supply rail collapses during switch-on current demand → output droops → erratic regulation and potential latch-up.
Output capacitor — ≥100µF electrolytic Selection: ESR < 200mΩ to keep output ripple below 50mVpp. Voltage rating ≥ 46V. Failure mode: High-ESR electrolytic: output ripple voltage = ESR × ΔIL. At 1A ripple and 500mΩ ESR → 500mVpp ripple — exceeds spec for virtually all loads.
Feedback resistors R1 / R2 — R1 = 1.21kΩ (1%), R2 = R1 × (Vout/1.2 − 1) Selection: 1% metal-film tolerance minimum. R1 sets the bias current into the FB divider; values 1.21kΩ–10kΩ keep FB current in the datasheet-recommended range. Failure mode: 5% resistors introduce ±5% Vout error. R1 too large (>100kΩ) → FB pin susceptible to noise injection → oscillation or false regulation.
Design Equations
Output voltage: Vout = 1.2V × (1 + R2/R1)
R1 is typically 1.21kΩ–10kΩ (1% tolerance). Solve for R2: R2 = R1 × (Vout/1.2 - 1). Example: for 5V with R1=1.21kΩ → R2 ≈ 3.74kΩ (use 3.74kΩ 1%).
Inductor sizing: At Vin=22V→Vout=5.5V: range is 33–68µH (30%→15% current ripple). Use 68µH for good regulation; 33µH acceptable if BOM cost is critical. Isat must be ≥ 3.8A — under-sizing Isat is the leading cause of field failures: the inductor saturates under peak current, spiking IC switch current beyond its rating.
Gotchas
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[Mistake]: Assuming the TO-263 package requires a heat sink like the TO-220 variant.
What happens: Excessive junction temperature rise causes thermal shutdown or permanent damage because the PCB copper area is insufficient to dissipate power.
Fix: Ensure at least 0.4 in² copper area under the tab, preferably 2 in² of 2 oz copper, and verify thermal design per datasheet recommendations. -
[Mistake]: Routing feedback (FB) trace too close to the SW pin or noisy switching nodes.
What happens: Noise couples into the feedback input, causing output voltage instability, oscillation, or erroneous regulation.
Fix: Route FB away from SW node and use a star ground connection to minimize noise coupling. -
[Mistake]: Operating continuously above 3A output current rating.
What happens: The device overheats, leading to thermal runaway and eventual device failure despite internal thermal shutdown attempts.
Fix: Design load current below 3A or use a device or topology rated for higher current. -
[Mistake]: Using minimal or no input and output bypass capacitors per datasheet recommendations.
What happens: Increased voltage ripple and switching node voltage spikes cause premature component stress and potential latch-up or false triggering of protection circuits.
Fix: Place recommended input and output filter capacitors as close to the device pins as possible, with low ESR types to stabilize operation.