Analog Devices Inc. LTC4125EUFD#PBF

Overview

LTC4125EUFD#PBF from Analog Devices (formerly Linear Technology) is a monolithic 5W AutoResonant wireless power transmitter IC that drives a full-bridge LC tank to deliver regulated power across an air gap. It features integrated 100mΩ MOSFETs, programmable input current limiting (0.785–0.815V threshold), NTC-based temperature monitoring, and multi-method foreign object detection. It operates in industrial handhelds and medical equipment requiring contactless charging with fault-safe operation.

For engineers reviewing the LTC4125EUFD#PBF datasheet, LTC4125EUFD#PBF pinout, LTC4125EUFD#PBF application, or LTC4125EUFD#PBF equivalent, key selection considerations include its 50kHz–250kHz AutoResonant frequency tracking, 3V–5.5V input range, 20-pin 4mm × 5mm QFN package, dual-input current sense interface (IS+/IS−), and FB-based load detection for adaptive power delivery.

Technical Context

The LTC4125EUFD#PBF implements a patent-pending AutoResonant control architecture that continuously adjusts switching frequency to match the series LC tank's resonant frequency-enabling maximum power transfer despite coil inductance drift or temperature variation. Its internal full-bridge driver uses pulse-width modulation synchronized to tank zero-crossing to maintain phase alignment between SW1/SW2 voltage and coil current.

Power optimization is achieved via periodic transmit power search: the device performs linear pulse-width ramping while monitoring FB voltage and IMON current, halting at the first valid exit condition-either sufficient receiver load detection (ΔV_FB step), input current threshold crossing (0.800V), or fault activation (FTH/NTC/DTH). Fault responses include immediate power shutdown and STAT pin high-impedance assertion.

Key Specifications

Pinout & Package

Package: 20-lead plastic QFN (UFD20), 4mm × 5mm, 0.75mm profile, exposed thermal pad (Pin 21) must be connected to GND.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar wireless power transmitter applications.

Compared with BQ51221RGER and MP-A21, the LTC4125EUFD#PBF delivers higher autonomous power (5W vs. ≤4W), eliminates need for external MCU or certification overhead, and provides direct analog interfaces (FB, NTC, FTH) for deterministic, real-time fault response in safety-critical embedded systems.

Availability

LTC4125EUFD#PBF is available at Aetrix Electronics and suitable for medical equipment, industrial handhelds, and military field sensors requiring stable component supply, long-term lifecycle support, and guaranteed RoHS-compliant lead-free packaging.

Supply support for LTC4125EUFD#PBF includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Analog Devices acquired Linear Technology in 2017 and maintains its precision analog and power management product lines with full datasheet, simulation model, and application note support.

The LTC4125EUFD#PBF belongs to Linear's wireless power controller family, designed specifically for high-efficiency, fault-resilient, and self-tuning resonant power transmission in space-constrained, safety-regulated environments.

FAQ

What is the primary function of the LTC4125EUFD#PBF in a wireless power system?

The LTC4125EUFD#PBF serves as a fully autonomous wireless power transmitter controller. It drives a series LC tank via an integrated full-bridge to deliver over 5W across an air gap. Its core functions include AutoResonant frequency tracking, Optimum Power Search for load-matched transmission, and multi-method foreign object detection - all implemented without external microcontroller intervention. The LTC4125EUFD#PBF replaces discrete gate drivers, controllers, and protection circuitry with a single IC optimized for reliability in medical and industrial settings.

How does the LTC4125EUFD#PBF detect foreign objects during wireless power transfer?

The LTC4125EUFD#PBF employs four independent foreign object detection mechanisms: (1) FTH pin monitors resonant frequency shift - a conductive object lowers tank inductance, raising frequency above the programmed threshold; (2) DTH pin detects abnormally small ΔV_FB steps during power search, indicating weak coupling or lossy material; (3) NTC pin senses temperature rise via thermistor voltage drop; and (4) ILIM comparator triggers immediate shutdown if input current exceeds 1.200V at IMON. All four methods operate concurrently and cause power cessation within microseconds. The LTC4125EUFD#PBF does not rely on communication protocols but uses direct analog sensing for deterministic response.

Can the LTC4125EUFD#PBF operate with different LC tank configurations?

Yes, the LTC4125EUFD#PBF supports both full-bridge and half-bridge LC tank topologies. For full-bridge operation - delivering maximum power - connect the series LC network between SW1 and SW2. For half-bridge operation - useful in space-constrained designs - connect the LC network between SW1 and GND. The AutoResonant engine automatically adapts to the tank's natural frequency regardless of L (e.g., 24µH) or C (e.g., 100nF) values, and the CTS/CTD pins allow tuning of search settling time (1ms–20ms) and inter-search delay (≥1s). The LTC4125EUFD#PBF's 50kHz–250kHz operating range accommodates a wide variety of coil geometries and coupling coefficients.

What is the role of the FB pin in the LTC4125EUFD#PBF, and how is it configured?

The FB (Feedback) pin on the LTC4125EUFD#PBF monitors the rectified peak voltage across the transmit LC tank via a resistor divider (e.g., R_FB1/R_FB2). During the Optimum Power Search, the LTC4125EUFD#PBF increments pulse width and measures resulting ΔV_FB; a large step indicates the receiver load has been satisfied. If FB voltage exceeds VIN (over-range threshold), the device halts transmission - protecting against open-circuit or mismatched receiver conditions. The FB pin leakage is ≤1.2µA, and its over-range hysteresis is 40mV. Leaving FB unconnected or shorting it to GND disables auto-load detection, forcing fixed-power operation. The LTC4125EUFD#PBF requires no external compensation on this pin.

Does the LTC4125EUFD#PBF require external components for basic operation, and what are the critical ones?

Yes, the LTC4125EUFD#PBF requires several external components for safe and functional operation: (1) Three bypass capacitors - 1µF on IN, 47µF on IN1, 47µF on IN2; (2) Series LC tank connected between SW1 and SW2 (or SW1–GND); (3) Resistor divider from tank rectified peak to FB; (4) Sense resistor (R_IS) between input supply and IS–, with R_IN and R_IMON setting current thresholds; (5) NTC thermistor from NTC to GND and pull-up resistor from IN to NTC; (6) Capacitors on CTS (1–20ms settling) and CTD (≥1s delay) pins. The LTC4125EUFD#PBF integrates all power switches, drivers, comparators, and oscillators - eliminating need for gate drivers, op-amps, or microcontrollers.