**LTC4121IUD#PBF: A 400mA Automatic Resonant Wireless Charger with Constant-Current/Constant-Voltage Operation and Thermal Regulation**

The proliferation of portable electronic devices has driven the demand for robust and efficient wireless power solutions. At the forefront of this innovation is the **LTC4121IUD#PBF** from Analog Devices, a sophisticated automatic resonant wireless power receiver IC designed to deliver a seamless and safe charging experience. This device integrates a high-efficiency full-wave bridge rectifier, a resonant receiver, and a sophisticated battery charger into a single, compact package, making it an ideal solution for space-constrained applications requiring up to **400mA of charging current**.

A standout feature of the LTC4121 is its **automatic and seamless transition between constant-current (CC) and constant-voltage (CV) modes**. This intelligence is critical for the health and longevity of lithium-ion/polymer batteries. The charger initiates the cycle by delivering a steady, regulated current to a deeply discharged battery. Once the battery voltage ascends to the predetermined float voltage, the IC automatically switches to regulating voltage, tapering the current to a trickle charge until the battery is full. This precise control eliminates the risk of overcharging, ensuring both safety and maximum battery capacity over its lifetime.

The IC employs **resonant wireless power transfer technology**, which offers significant advantages over older inductive methods. Resonance allows for greater spatial freedom between the transmitter and receiver coils, enabling more flexible product design and a more forgiving user experience. Furthermore, this technology generally provides higher efficiency across a wider range of operating conditions, translating to less wasted energy and reduced heat generation.

However, managing heat is paramount in any power system. The LTC4121 incorporates an advanced **thermal regulation loop** that actively protects both the IC itself and the battery being charged. If the internal die temperature exceeds approximately 115°C, the charger autonomously reduces the charging current. This proactive throttling mechanism prevents thermal runaway and potential damage, allowing the system to operate reliably even in elevated ambient temperatures or under poor coupling conditions.

Housed in a tiny 3mm x 3mm 12-lead QFN package, the LTC4121IUD#PBF provides a highly integrated solution. Its minimal external component count simplifies design-in for applications such as medical instruments, industrial sensors, wearable devices, and a host of other consumer electronics where a physical connector is undesirable or impractical.

**ICGOODFIND:** The LTC4121IUD#PBF stands out as a highly integrated, intelligent, and safe solution for wireless battery charging. Its combination of **automatic CC/CV operation**, efficient **resonant power reception**, and robust **thermal regulation** makes it a superior choice for designers seeking reliability and performance in a compact form factor.

**Keywords:** Wireless Charger, Constant-Current Constant-Voltage, Thermal Regulation, Resonant Receiver, Battery Management.