Key Specs
| Spec | Value | Condition | Source |
|---|---|---|---|
| Function | Step-Down | Digi-Key | |
| Output Configuration | Positive | Digi-Key | |
| Topology | Buck | Digi-Key | |
| Output Type | Adjustable | Digi-Key | |
| Number Of Outputs | 1 | Digi-Key | |
| Input Voltage (Min) | 5V | Digi-Key | |
| Input Voltage (Max) | 16V | Digi-Key | |
| Output Voltage (Min) | 0.4V | Digi-Key | |
| Output Voltage (Max) | 5.8V | Digi-Key | |
| Output Current (Max) | 60A | Digi-Key | |
| Switching Frequency (Typ) | 308kHz ~ 2MHz | Digi-Key | |
| Synchronous Rectifier | No | Digi-Key | |
| Operating Temperature Range | -40°C ~ 125°C (TJ) | Digi-Key | |
| Grade | - | Digi-Key | |
| Qualification | - | Digi-Key | |
| Mounting Type | Surface Mount | Digi-Key | |
| Package Case | 36-PowerVFQFN | Digi-Key | |
| Supplier Device Package | 36-FC2QFN (4.25x10) | Digi-Key |
When To Use
Use the MAX20860AAFX+T in applications requiring a high-current, single-output, adjustable step-down (buck) regulator with input voltages from 5V to 16V and output voltages adjustable between 0.4V and 5.8V. It is ideal for powering high-performance processors, FPGAs, or ASICs where a maximum output current of 60A is required and switching frequencies between 308kHz and 2MHz are desired for efficiency and size optimization.
Do not use this device in synchronous rectifier applications, as it does not support synchronous rectification, or in systems requiring input voltages below 2.7V or above 16V. For input voltages outside this range or synchronous operation, consider alternative devices designed for wider input voltage ranges or synchronous buck topologies.
When Not To Use
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>60A output current required: The maximum output current is 60A, with phase overcurrent protection at 55A per phase. For loads exceeding this, use a multi-phase buck controller designed to safely and efficiently handle higher currents.
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Efficiency-critical designs requiring synchronous rectification: This part has no synchronous rectifier, so diode losses reduce efficiency and increase heat dissipation. Use a synchronous buck controller to avoid shoot-through and minimize conduction losses.
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Switching frequency > 500kHz needed for small inductors: Although the max switching frequency is 2MHz, typical operation is around 400kHz. For consistent high-frequency operation above 500kHz with tight control, use a high-frequency buck controller specialized for stable switching at those frequencies.
Application Notes
The LX1 node is the primary switching node and experiences high dv/dt and di/dt; it requires the smallest possible loop area to minimize EMI and switching losses. Place the bootstrap capacitor (BST to LX) as close as possible to these pins to ensure reliable high-side MOSF
Minimum External Components
Catch diode — Schottky, Vr ≥ 16V, If ≥ 60A Selection: Schottky forward recovery < 10ns vs 200–500ns for silicon. At 308kHz (period = 3.2µs), a 500ns-recovery diode is off for only 2.7µs before the next switch-on — it never fully turns off. Failure mode: Standard silicon rectifier: 200–500ns reverse recovery at 308kHz causes shoot-through current spikes every cycle — IC switch current exceeds rating, causing thermal runaway or immediate failure.
Output inductor — 4µH Selection: Isat ≥ 75.0A (peak current at max load). DCR < 100mΩ to limit conduction loss. At Vin=10V→Vout=0.9V: range is 5–5µH (30%→15% current ripple). Use 4µH for good regulation; 4µH acceptable if BOM cost is critical. Isat must be ≥ 75.0A — 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 ≥ 16V 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 ≥ 7V. 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/0.4 − 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 = 0.4V × (1 + R2/R1)
R1 is typically 1.21kΩ–10kΩ (1% tolerance). Solve for R2: R2 = R1 × (Vout/0.4 - 1). Example: for 5V with R1=1.21kΩ → R2 ≈ 3.74kΩ (use 3.74kΩ 1%).
Inductor sizing: At Vin=10V→Vout=0.9V: range is 5–5µH (30%→15% current ripple). Use 4µH for good regulation; 4µH acceptable if BOM cost is critical. Isat must be ≥ 75.0A — 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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Incorrect Input Voltage Range Application
- Mistake: Applying input voltage below 2.7V or above 16V.
- Failure Mode: Device may enter undervoltage lockout or overvoltage conditions, causing malfunction or permanent damage.
- Fix: Verify input voltage range strictly adheres to 2.7V minimum and 16V maximum. Use appropriate input voltage protection or select a device rated for the required input range.
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Inadequate Bootstrap Capacitor Selection
- Mistake: Using a bootstrap capacitor with voltage rating below +25.5V or placing it far from BST and LX pins.
- Failure Mode: Bootstrap circuit fails, leading to improper high-side MOSFET drive, increased switching losses, and possible device failure.
- Fix: Use a 0.47μF ceramic capacitor with voltage rating above +25.5V, placed as close as possible to BST and LX pins.
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Insufficient Thermal Management
- Mistake: Operating at or near 60A output current without adequate heatsinking or PCB copper area.
- Failure Mode: Junction temperature exceeds +125°C, triggering thermal shutdown or causing permanent damage.
- Fix: Implement proper thermal design including heatsinks or sufficient PCB copper area to maintain junction temperature below +125°C.