LT3502AEDC#TRPBF is a high-efficiency, 40 V input, monolithic step-down (buck) DC/DC switching regulator designed and manufactured by Analog Devices Inc. (following its acquisition of Linear Technology). It belongs to the robust LT35xx family of current-mode PWM regulators — engineered for demanding industrial, automotive, and medical applications where wide input range, high reliability, and low EMI are critical. The “A” denotes the improved second-generation version with enhanced stability, tighter tolerance, and lower quiescent current; “EDC” specifies the 10-lead (3 mm × 3 mm) DFN package with exposed pad; and “#TRPBF” indicates tape-and-reel packaging (2,500 units per reel), Pb-free, and RoHS-compliant.
Introduction
The LT3502AEDC#TRPBF integrates a 40 V, 1.2 A peak-switching-current power MOSFET, a precision reference, oscillator, error amplifier, and current-sense circuitry into a compact 10-lead DFN package. It operates from an ultra-wide input voltage range of 3.6 V to 40 V, making it ideal for systems powered by unregulated 12 V/24 V/36 V rails — including automotive (cold-crank down to 3.6 V), industrial sensors (24 V PLC buses), and battery-powered equipment (e.g., 12 V LiFePO₄ or 4S Li-ion packs). Its current-mode control architecture delivers excellent line and load transient response, inherent cycle-by-cycle current limiting, and easy compensation — even with high-ESR ceramic or polymer output capacitors.
The device supports adjustable output voltages from 0.8 V to VIN – 1.2 V, with ±1% reference accuracy over temperature and line/load. It features programmable soft-start (via external capacitor), power-good (PG) indicator, precision enable threshold (2.5 V ±100 mV), and integrated bootstrap diode, eliminating the need for an external Schottky diode and simplifying layout. The “A” revision improves startup reliability under light loads and reduces no-load IQ to just 70 µA (typ.), enabling always-on operation in energy-sensitive applications.
The EDC package (3 mm × 3 mm DFN) includes an exposed thermal pad (EP) that — when properly soldered to a PCB ground plane — achieves θJA ≈ 45°C/W, supporting continuous 1.2 A output at ambient temperatures up to +85°C without external heatsinking.
Key Features
✅ Ultra-Wide Input Range: 3.6 V to 40 V — supports automotive cold-crank, industrial 24 V, and multi-cell battery inputs.
✅ High Efficiency & Low Quiescent Current: Up to 95% peak efficiency; only 70 µA (typ.) no-load IQ, enabling long battery life and “always-on” monitoring modes.
✅ Integrated 40 V / 1.2 A Power Switch: Eliminates external MOSFETs and gate drivers — reducing solution size and component count.
✅ Precision Reference & Regulation: ±1% output voltage accuracy over line, load, and temperature (–40°C to +125°C); 0.8 V internal reference enables low-output designs (e.g., 1.0 V, 1.2 V, 1.8 V, 3.3 V, 5 V).
✅ Robust Protection Features:
• Cycle-by-cycle peak current limit;
• Thermal shutdown with hysteresis;
• Output overvoltage protection (OVP) via internal clamp;
• Undervoltage lockout (UVLO) with precise 2.5 V EN threshold (±100 mV).
✅ Low-EMI Design Enablers:
• Internal compensation (reduces external parts);
• Programmable switching frequency (200 kHz to 2.2 MHz) — allows optimization for efficiency (low fSW) or small size (high fSW);
• Optional spread-spectrum frequency modulation (SSFM) to reduce peak EMI emissions.
✅ System-Level Integration:
• Integrated bootstrap diode — no external Schottky required;
• Power-good (PG) open-drain output for system sequencing and fault reporting;
• Adjustable soft-start (via external capacitor) prevents inrush current and output overshoot.
Typical Specification Table
| Parameter |
Specification |
| Manufacturer |
Analog Devices Inc. (formerly Linear Technology) |
| Product Series |
LT35xx Family (High-Voltage Monolithic Buck Regulators) |
| Model |
LT3502AEDC#TRPBF |
| Function |
Monolithic Step-Down (Buck) DC/DC Converter |
| Input Voltage Range |
3.6 V to 40 V |
| Output Voltage Range |
0.8 V to VIN – 1.2 V (adjustable via feedback divider) |
| Max Output Current |
1.2 A (continuous, with proper thermal design) |
| Switching Frequency |
200 kHz to 2.2 MHz (externally programmable) |
| Efficiency (typ.) |
Up to 95% (e.g., 12 V → 3.3 V @ 1 A) |
| Quiescent Current (IQ) |
70 µA (no-load, 12 VIN, 3.3 VOUT) |
| Reference Accuracy |
±1% (over line, load, temperature: –40°C to +125°C) |
| Enable Threshold (EN) |
2.5 V ±100 mV (hysteresis = 120 mV) |
| Power-Good (PG) |
Open-drain, active-high when VOUT is within ±7.5% |
| Soft-Start |
Adjustable via external capacitor (CSS) |
| Operating Junction Temp. |
–40°C to +125°C (guaranteed) |
| Package |
10-Lead (3 mm × 3 mm) DFN with Exposed Pad (EDC) |
| RoHS / Green |
Yes (Pb-free, Halogen-free) |
| Packaging |
Tape-and-Reel (TR), 2,500 units per reel (PBF) |
Typical Applications
🔹 Automotive Electronics: Camera modules, ADAS ECUs, infotainment head units, and body control modules — leveraging 40 V rating to survive load-dump transients (ISO 7637-2, Pulse 5a/b) and cold-crank operation down to 3.6 V.
🔹 Industrial Sensors & PLC I/O: Powering 3.3 V or 5 V microcontrollers, ADCs, and RS-485 transceivers from noisy 24 V factory buses — enabled by wide VIN, high PSRR, and robust UVLO.
🔹 Medical Devices: Portable ultrasound, patient monitors, and infusion pumps — benefiting from low EMI (SSFM-capable), high reliability, and quiet operation (no audible coil whine due to stable current-mode control).
🔹 Battery-Powered Test Equipment: Handheld multimeters, data loggers, and field calibrators — where 70 µA IQ extends battery life and wide VIN supports multiple chemistries (Li-ion, LiFePO₄, NiMH).
🔹 Distributed Power Architectures: Intermediate bus conversion (e.g., 24 V → 5 V/3.3 V) in telecom shelves, base stations, and edge servers — simplified by integrated switch and bootstrap diode.
🔹 LED Drivers & Bias Supplies: Driving logic-level MOSFET gates or powering op-amp rails in precision analog front-ends — using adjustable VOUT and tight regulation.
Development & Design Notes
🔧 Thermal Management & Layout:
- Solder the exposed pad (EP) to a ≥ 100 mm² internal ground plane using ≥ 9 thermal vias (0.3 mm diameter) — essential for maintaining TJ < 125°C at full 1.2 A load and +85°C ambient.
- Keep power loops (VIN → SW → L1 → OUT → GND) extremely short and wide; use solid copper pours for VIN, SW, and PGND — minimizes EMI and switching losses.
🔧 Inductor & Capacitor Selection:
- Choose shielded power inductors rated for ≥ 1.5 A saturation current (e.g., Coilcraft XAL5030, Würth WE-PD). Avoid unshielded types — they radiate strongly.
- Use low-ESR ceramic output capacitors (e.g., 22 µF × 2 in parallel, X5R/X7R, 6.3 V rating). Place them < 3 mm from SW and GND pins — critical for stability and transient response.
🔧 Frequency & EMI Optimization:
- For lowest EMI: set fSW = 400–600 kHz (reduces harmonics) and enable SSFM (via SYNC pin tied to resistor to GND).
- For smallest solution size: use fSW = 2.2 MHz and 1 µH inductor (e.g., 1.0 × 0.6 mm chip inductor). Verify loop stability — the LT3502A’s internal compensation is optimized for 200 kHz–2.2 MHz.
🔧 Enable & Sequencing Design:
- Use the precise 2.5 V EN threshold to sequence with other rails (e.g., tie EN to a 2.5 V supervisor or another regulator’s PG pin). Add a 10 nF capacitor from EN to GND for noise immunity.
- Configure PG to drive a microcontroller GPIO or reset generator — enables safe power-up/down sequencing and brown-out detection.
🔧 Reliability & Safety:
- Add a 12 V TVS diode (e.g., SMAJ12A) on VIN for automotive load-dump protection (though LT3502A withstands 40 V continuously, it’s not rated for 60 V/100 ms pulses).
- For functional safety (IEC 61508), monitor PG and thermal warning (via junction temp estimation using RθJA and power dissipation) — ADI provides FIT rate data and reliability reports.
