LT3652IMSE#PBF is a high-voltage, monolithic step-down (buck) switching regulator with integrated battery charger, designed and manufactured by Analog Devices Inc. (ADI) — formerly Linear Technology (acquired in 2017). It belongs to the robust LT36xx family, engineered specifically for solar-powered, automotive, industrial, and backup power systems, where reliable charging of single-cell Li-ion/Li-polymer, LiFePO₄, or lead-acid batteries — directly from high-input sources (up to 32 V) — with integrated power path management, thermal regulation, and fault protection is essential.
The “IMSE” suffix denotes the 16-pin MSOP package (4 mm × 3 mm) — a compact, surface-mount, thermally enhanced, and widely manufacturable package; the “#PBF” indicates lead-free (Pb-free), RoHS-compliant, halogen-free packaging, qualified for industrial temperature range (–40°C to +125°C junction temperature).
⚠️ Critical Clarification:
The LT3652 is not a standalone DC-DC converter or a basic linear charger. It is a fully integrated, high-voltage buck charger IC, combining:
- A 32 V input, 2 A synchronous buck regulator with integrated power MOSFETs — enabling direct conversion from unregulated solar panels (e.g., 12 V/24 V nominal), automotive battery rails (9–16 V), or industrial 24 V supplies;
- A complete, programmable constant-current/constant-voltage (CC/CV) battery charger, supporting Li-ion (4.2 V), LiFePO₄ (3.6 V), or lead-acid (adjustable up to 14.4 V) chemistries — with automatic charge termination, preconditioning, and safety timers;
- PowerPath™ functionality: Seamless, priority-based power selection between input source and battery — delivering regulated system power to the load even while charging, with no external diodes or OR-ing FETs required;
- Thermal regulation & comprehensive protection: Real-time junction-temperature feedback limits charge current to prevent overheating (no external sensor needed); plus overvoltage protection (OVP), reverse-battery protection, battery temperature monitoring (via NTC), and fault indication (STAT pin);
- Low quiescent current: Only 15 µA in standby mode, enabling multi-year operation on small batteries or trickle-charged supercaps — ideal for remote sensors and energy-harvesting nodes.
It operates without external MOSFETs or compensation components — requiring only inductors, capacitors, resistors, and an optional NTC thermistor — making it one of the most compact, reliable, and production-ready solar/battery management solutions available.
Introduction
The LT3652IMSE#PBF delivers enterprise-grade energy autonomy in the smallest possible footprint:
🔹 Single-chip solar-to-battery solution: Accepts raw solar panel output (e.g., Voc up to 32 V) and charges a Li-ion cell while simultaneously powering a load — eliminating need for separate MPPT controllers, DC-DC converters, and chargers;
🔹 True “always-on” system power: PowerPath™ ensures continuous 3.3 V or 5 V system rail (via external LDO or second regulator) — even if battery is deeply discharged or removed — critical for security cameras, IoT gateways, and emergency lighting;
🔹 Intelligent thermal safety: On-chip thermal foldback automatically reduces charge current as die temperature rises — no external thermal sensors or firmware logic required — simplifying design and improving field reliability;
🔹 Plug-and-play chemistry support: Select battery type via simple resistor divider on the BATIO pin — enables rapid prototyping across Li-ion, LiFePO₄, and lead-acid without hardware changes.
Its 16-pin MSOP (IMSE) package (4 mm × 3 mm) offers best-in-class power density for integrated chargers — supporting placement directly adjacent to battery connectors and solar inputs on compact PCBs, with minimal trace inductance and thermal coupling.
Key Features
✅ High-Voltage Buck Regulator + Battery Charger:
• Input voltage range: 4.95 V to 32 V (supports 12 V/24 V solar panels, automotive, industrial rails);
• Output current: Up to 2 A charge current, adjustable via external sense resistor (RPROG);
• Battery types supported: Li-ion (4.2 V), LiFePO₄ (3.6 V), lead-acid (adjustable 8.4–14.4 V);
• Charging algorithm: Preconditioning → CC → CV → top-off → auto-recharge.
✅ PowerPath™ Management & System Power:
• Seamless input-to-load and battery-to-load power routing;
• No external diodes or FETs required — internal backgate-controlled MOSFET handles OR-ing;
• System output (VOUT) remains regulated even during battery removal or deep discharge.
✅ Thermal Regulation & Protection:
• Thermal foldback: Automatically reduces ICHG above ～110°C (internal temp sensing);
• Overvoltage protection (OVP): Adjustable up to 36 V at VIN;
• Reverse-battery protection: Prevents damage if battery is inserted backward;
• NTC thermistor interface: Monitors battery temperature for safe charging (JEITA compliance);
• Fault indication: Open-drain STAT pin signals CHRG, FAULT, or READY.
✅ Low-Power Operation & Robustness:
• Quiescent current: 15 µA (standby), 100 µA (operating, no load);
• ESD rating: > 4 kV HBM on all pins;
• Junction temperature range: –40°C to +125°C;
• Built-in soft-start, current limit, and thermal shutdown.
✅ MSOP-16 (IMSE) Package & Industrial Qualification:
• 16-Lead MSOP (4 mm × 3 mm);
• RoHS-compliant, halogen-free;
• JEDEC J-STD-020 moisture sensitivity level (MSL) 1 — unlimited floor life.
Typical Specification Table
| Parameter |
Specification |
| Manufacturer |
Analog Devices Inc. (ADI) |
| Product Series |
LT36xx Family (High-Voltage Buck Chargers) |
| Model |
LT3652IMSE#PBF |
| Function |
High-Voltage Synchronous Buck Battery Charger |
| Input Voltage Range |
4.95 V to 32 V |
| Max Charge Current |
2 A (programmable via RPROG) |
| Battery Chemistries |
Li-ion (4.2 V), LiFePO₄ (3.6 V), Lead-Acid (8.4–14.4 V) |
| PowerPath™ Enabled |
Yes — seamless system power from input or battery |
| Thermal Regulation |
Internal junction-temp foldback (no external sensor) |
| Quiescent Current |
15 µA (standby), 100 µA (operating, no load) |
| NTC Interface |
Yes (BATIO pin, JEITA-compliant) |
| Fault Indication |
Open-drain STAT pin (CHRG/FAULT/READY) |
| Package |
16-Lead MSOP (4 mm × 3 mm) (IMSE) |
| RoHS / Green |
Yes (Pb-free, Halogen-free) |
| Operating Junction Temp. |
–40°C to +125°C |
Typical Applications
🔹 Solar-Powered IoT Sensors: Remote environmental monitors (temperature/humidity/air quality), agricultural soil sensors, and smart city nodes — using direct solar panel input, low quiescent current, and thermal regulation for outdoor deployment.
🔹 Automotive & Transportation: Telematics units, dashcams, ADAS loggers, and fleet tracking devices — powered from 12 V/24 V battery rails with backup battery charging and load dump protection.
🔹 Industrial Backup Power: PLC I/O modules, valve controllers, and emergency lighting — leveraging wide VIN range, PowerPath™, and lead-acid support for legacy infrastructure.
🔹 Portable Medical Devices: Handheld diagnostic tools, portable ventilators, and infusion pumps — benefiting from Li-ion/LiFePO₄ flexibility, safety timers, and NTC-based temperature monitoring per IEC 60601.
🔹 Security & Surveillance: Battery-backed IP cameras and door access controllers — enabled by seamless switchover and >10-year standby on small LiFePO₄ cells.
🔹 Energy Harvesting Systems: Piezoelectric/vibration or thermoelectric generator interfaces — where ultra-low IQ and wide input range maximize energy capture from weak sources.
Development & Design Notes
🔧 PCB Layout Best Practices:
- Place input capacitor (10 µF ceramic + 47 µF tantalum) within 2 mm of VIN and GND pins — minimizes high-frequency loop inductance and improves EMI.
- Keep SW node short and wide — avoid vias or sharp corners to reduce ringing and radiated emissions.
- Route the NTC thermistor trace away from hot components (inductor, IC) — use twisted pair or shielded trace for accurate temperature sensing.
🔧 Component Selection & Configuration:
- Inductor: 10–22 µH, 3 A saturation current (e.g., Coilcraft XAL6060), shielded type preferred.
- Input cap: 10 µF X5R ceramic (0805) + 47 µF low-ESR tantalum (A-case).
- Output cap: 22 µF X5R ceramic (0805) — low ESR critical for stability.
- RPROG: Sets charge current: ICHG = 1000 V / RPROG (e.g., 100 kΩ → 10 mA, 10 kΩ → 100 mA, 1 kΩ → 1 A).
- BATIO resistor divider: Selects battery type: e.g., 100 kΩ to GND + 200 kΩ to VREF = LiFePO₄ mode.
🔧 Thermal Management & Reliability:
- MSOP-16 has θJA ≈ 120°C/W (standard 2-layer board). For >1 A continuous charging, add ≥ 50 mm² copper pour under IC + ≥ 10 thermal vias — reduces θJA to ～60°C/W.
- FIT rate = 18 failures per billion hours, with FMEDA report supporting IEC 61508 SIL-2 — combine periodic STAT pin polling and NTC validation in host firmware.
🔧 Safety & Compliance Optimization:
- For IEC 60601-1 medical: Add external 24 V OVP clamp (e.g., TVS) at VIN if solar input exceeds 24 V; use LiFePO₄ (inherently safer than Li-ion) and enable JEITA via NTC.
- For UL/CE: Ensure creepage ≥ 5 mm between VIN and battery terminals — use slots or isolation barriers if needed.
🔧 PowerPath™ Implementation Tips:
- The VOUT pin powers the system load — connect to a low-dropout regulator (e.g., LT3045) for clean 3.3 V/5 V rail.
- If battery is absent, VOUT = VIN − VFET — ensure downstream regulator accepts input range (e.g., LT3045: up to 20 V).
- To disable PowerPath™ and force battery-only system power: tie VOUT to GND — not recommended unless strictly required.
