MAX745EAP+T is a high-efficiency, 28 V input, synchronous step-down (buck) DC/DC controller designed and manufactured by Analog Devices Inc. (following its acquisition of Maxim Integrated). It belongs to the robust MAX74x family of current-mode PWM controllers — engineered for industrial, automotive, and telecom applications requiring wide input range, high reliability, and precise output regulation. The “EAP” suffix denotes the 20-pin SSOP (Shrink Small Outline Package), optimized for thermal performance and manufacturability; the “+T” indicates tape-and-reel packaging (2,500 units per reel), Pb-free, and RoHS-compliant.
â ī¸ Important Clarification:
The part number MAX745EAP+T is not a monolithic regulator (i.e., it does not integrate power MOSFETs). Instead, it is a controller IC — meaning it drives external high-side and low-side N-channel MOSFETs, enabling system designers to optimize efficiency, power level, and thermal design for their specific application (e.g., 3 A, 5 A, or 10 A output). This architecture provides superior flexibility and scalability compared to fixed-output monolithic ICs — especially in high-current or high-temperature environments.
Introduction
The MAX745EAP+T is a precision, current-mode, synchronous buck controller operating from an ultra-wide input voltage range of 4.5 V to 28 V, with support for output voltages as low as 0.6 V (set by an external resistor divider) and capable of delivering multi-ampere output currents, depending on the selected external MOSFETs and inductor. Its key innovation lies in its adaptive on-time (AOT) control architecture, which enables:
- Instantaneous load transient response (no external compensation required);
- Stable operation across wide input/output ratios (e.g., 24 V → 1.2 V);
- Fixed switching frequency (300 kHz to 2.2 MHz) — programmable via external resistor (RFREQ), enabling optimization for efficiency (lower fSW) or compact size (higher fSW).
The device integrates essential system functions:
đš Precision 0.6 V reference (±1% over temperature) for tight output regulation;
đš Power-good (PGOOD) output with adjustable delay and hysteresis;
đš Programmable soft-start (via external capacitor) to limit inrush current;
đš Thermal shutdown, overcurrent protection (OCP) with hiccup mode, and undervoltage lockout (UVLO) with 200 mV hysteresis;
đš Synchronous MOSFET gate drivers with adaptive dead-time control — minimizing shoot-through losses and maximizing efficiency.
The EAP package (20-pin SSOP, 7.2 mm × 5.3 mm, 0.65 mm pitch) features an exposed thermal pad (EP) that — when soldered to a multi-layer PCB ground plane — achieves θJA ≈ 40°C/W, supporting continuous high-current operation at ambient temperatures up to +85°C.
Key Features
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Wide Input Range & High Flexibility:
• VIN = 4.5 V to 28 V — ideal for 12 V/24 V industrial buses, automotive (with pre-regulator), and telecom intermediate rails.
• VOUT = 0.6 V to VIN – 1.5 V — supports core logic (0.8 V–1.2 V), I/O (1.8 V–3.3 V), and analog (5 V) rails.
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Adaptive On-Time (AOT) Control:
• No loop compensation needed — simplifies design and improves stability under varying line/load conditions;
• Sub-µs transient response — maintains tight regulation during fast load steps (e.g., CPU burst modes);
• Fixed-frequency operation (300 kHz–2.2 MHz) — enables predictable EMI filtering.
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High-Efficiency Synchronous Operation:
• Integrated dual MOSFET drivers (1.5 A peak sink/source) with adaptive dead-time control;
• Supports discrete N-channel high-side + N-channel low-side MOSFETs — eliminates need for P-channel or bootstrap diodes;
• Typical efficiency > 94% (e.g., 12 V → 3.3 V @ 5 A).
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Precision Regulation & Protection:
• ±1% output voltage accuracy (0.6 V reference);
• Adjustable overcurrent threshold (via ROCSET) with cycle-by-cycle limiting and hiccup-mode recovery;
• Thermal shutdown with 15°C hysteresis;
• UVLO with precise 4.25 V turn-on / 4.05 V turn-off thresholds.
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System-Level Integration & Diagnostics:
• Open-drain PGOOD output — active after soft-start and when VOUT is within ±7.5%;
• Programmable soft-start time (via CSS capacitor);
• Enable input (EN) with precise 1.22 V threshold and hysteresis.
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Robust Industrial Design:
• ESD rating > 4 kV HBM;
• Operating junction temperature: –40°C to +125°C;
• SSOP-20 (EAP) package with exposed pad — thermally efficient and compatible with standard reflow profiles.
Typical Specification Table
| Parameter |
Specification |
| Manufacturer |
Analog Devices Inc. (formerly Maxim Integrated) |
| Product Series |
MAX74x Family (Synchronous Buck Controllers) |
| Model |
MAX745EAP+T |
| Function |
Synchronous Step-Down (Buck) Controller IC |
| Input Voltage Range |
4.5 V to 28 V |
| Output Voltage Range |
0.6 V to VIN – 1.5 V (adjustable) |
| Switching Frequency |
300 kHz to 2.2 MHz (externally programmable) |
| Control Architecture |
Adaptive On-Time (AOT), Current-Mode |
| Reference Voltage |
0.6 V (±1% over line, load, temperature) |
| Output Accuracy |
±1% (over full operating conditions) |
| Gate Drive Capability |
Dual 1.5 A peak drivers (HS + LS N-MOS) |
| Protection Features |
OCP (hiccup), Thermal Shutdown, UVLO, PGOOD |
| Soft-Start |
Adjustable via external capacitor (CSS) |
| Enable Threshold (EN) |
1.22 V (typ.), with hysteresis |
| Operating Junction Temp. |
–40°C to +125°C |
| Package |
20-Lead SSOP with Exposed Pad (EAP) |
| RoHS / Green |
Yes (Pb-free, Halogen-free) |
| Packaging |
Tape-and-Reel (T), 2,500 units per reel (+T) |
Typical Applications
đš Industrial Power Supplies: Distributed 3.3 V/5 V/12 V rails for PLCs, HMIs, and sensor nodes — leveraging wide VIN, high efficiency, and robust OCP.
đš Automotive Infotainment & ADAS ECUs: Secondary regulation from 12 V battery rail (after pre-regulator) — enabled by 28 V max rating and stable AOT control during cold-crank transients.
đš Telecom & Networking Equipment: Point-of-load (POL) conversion in base stations, routers, and optical modules — benefiting from fixed-frequency EMI control and high PSRR.
đš FPGA/CPU Core Power: Low-voltage, high-current supplies (e.g., 0.85 V @ 6 A) — using discrete MOSFETs for optimal thermal management and dynamic response.
đš Medical Imaging & Diagnostic Systems: Stable, low-noise analog/digital supply rails — where AOT’s fast transient response prevents dropout during detector readout bursts.
đš Battery-Powered Test Equipment: Efficient conversion from 2-cell Li-ion (up to 8.4 V) or 3-cell (up to 12.6 V) packs to precision analog rails — with low IQ (< 1 mA) in light-load modes.
Development & Design Notes
đ§ MOSFET & Inductor Selection:
- Choose matched N-channel MOSFET pairs with low Qg and RDS(on) (e.g., SiR872DP for HS, SiR826DP for LS). Ensure gate charge < 30 nC for clean switching at 2 MHz.
- Use shielded power inductors rated for ≥ 1.5× max DC current (e.g., Coilcraft XAL6060, Würth WE-PD). Place inductor close to SW node to minimize ringing.
đ§ Layout & Thermal Management:
- Connect the exposed pad (EP) to a ≥ 200 mm² internal ground plane using ≥ 12 thermal vias (0.3 mm). For 5 A+ designs, add a small external heatsink on the high-side MOSFET.
- Keep power loops (VIN → HS-SW → INDUCTOR → OUT → LS-GND → VIN) extremely short and wide — use copper pours, not traces. Route HS/LS gate drive paths symmetrically and away from sensitive analog nodes.
đ§ Frequency & EMI Optimization:
- Set fSW = 600 kHz for best efficiency/noise tradeoff; use 2.2 MHz only if board space is critical (requires smaller inductor/capacitors but higher switching losses).
- Add a 10 Ω resistor in series with each gate driver output to dampen gate oscillation and reduce EMI.
- Place 100 pF capacitor from SW node to GND to suppress high-frequency ringing — verify no impact on stability.
đ§ Soft-Start & Sequencing:
- Soft-start time tSS ≈ 1.1 × RSS × CSS; use CSS = 100 nF and RSS = 100 kΩ for īŊ11 ms ramp — prevents inrush into large output capacitors.
- Tie EN to a supervisor IC (e.g., MAX6326) for power sequencing; add 10 nF capacitor from EN to GND for noise immunity.
đ§ Reliability & Safety:
- For functional safety (IEC 61508 SIL-2), monitor PGOOD and thermal warning (via external NTC on heatsink) — MAX745 includes built-in thermal shutdown but no junction temp reporting.
- Add TVS diode (e.g., SMAJ24A) on VIN for 28 V-rated systems subjected to load-dump events — though MAX745 tolerates 28 V continuously, it is not rated for 40 V/100 ms pulses.
