Analog Devices Inc. LTC4121IUD-4.2#PBF

Overview

LTC4121IUD-4.2#PBF from Analog Devices (formerly Linear Technology) is a 400mA synchronous step-down Li-Ion/Polymer battery charger IC with fixed 4.2V float voltage, MPPT input regulation, and NTC temperature qualification. It operates from 4.4V to 40V input, delivers up to 95% efficiency, and integrates low-battery preconditioning, timer termination, auto-recharge, and fault detection for solar-powered industrial sensors.

For engineers reviewing the LTC4121IUD-4.2#PBF datasheet, LTC4121IUD-4.2#PBF pinout, LTC4121IUD-4.2#PBF application, or LTC4121IUD-4.2#PBF equivalent, key selection considerations include its fixed 4.2V float voltage, 16-pin 3mm × 3mm QFN package, ±1% VFLOAT accuracy, programmable 50–400mA charge current via PROG resistor, and integrated MPPT control for high-impedance sources like solar panels.

Technical Context

The LTC4121IUD-4.2#PBF implements a synchronous buck topology with internal high-side and low-side MOSFETs (RDSON = 0.8Ω / 0.5Ω), programmable switching frequency (750kHz or 1.5MHz via FREQ pin), and precision current-mode control. Its MPPT function samples open-circuit input voltage every ~28 seconds, compares it against a user-defined fraction (via MPPT pin divider), and dynamically reduces charge current to maintain VIN ≥ VMP.

It features dual-stage charging: linear pre-conditioning below 2.91V (VBATSNS), followed by constant-current/constant-voltage regulation ending at 4.200V ±0.6%, with recharge triggered at 2.107V (VBATSNS falling 93mV below VFLOAT). Fault detection includes bad battery timeout (30 min), NTC cold/hot thresholds (74%/36.5% of INTVCC), and undervoltage lockout (ΔVDUVLO = 80mV typical).

Key Specifications

Pinout & Package

Package: 16-lead (3mm × 3mm) plastic QFN with exposed thermal pad (Pin 17 = GND). Requires soldering of exposed pad to PCB ground plane for thermal and electrical performance.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar battery charger applications.

Compared with MAX17710G+T and BQ24650RGER, the LTC4121IUD-4.2#PBF uniquely integrates MPPT, 400mA synchronous switching, and NTC qualification in a 3mm × 3mm QFN-enabling solar-charged Li-Ion systems with minimal external components and no firmware dependency.

Availability

LTC4121IUD-4.2#PBF is available at Aetrix Electronics and suitable for solar-powered remote sensors, industrial handheld instruments, and military-grade asset trackers requiring stable component supply across extended temperature ranges (–40°C to 125°C).

Supply support for LTC4121IUD-4.2#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) is a global leader in high-performance analog, mixed-signal, and power management semiconductors, serving industrial, automotive, communications, and aerospace markets.

The LTC4121IUD-4.2#PBF belongs to Linear's precision battery charger product line, engineered specifically for energy-constrained, high-impedance input applications such as solar-powered IoT and portable instrumentation where MPPT and thermal safety are critical.

FAQ

What is the fixed float voltage of the LTC4121IUD-4.2#PBF?

The LTC4121IUD-4.2#PBF has a factory-trimmed fixed float voltage of 4.200V ±0.6% (4.148V to 4.231V over temperature), optimized for single-cell Li-Ion and Li-Polymer batteries. This eliminates the need for external feedback resistors required by the programmable LTC4121 variant, simplifying design and improving voltage accuracy without calibration.

How does the MPPT function work in the LTC4121IUD-4.2#PBF?

The LTC4121IUD-4.2#PBF implements hardware-based MPPT by pausing charging every ~28 seconds for 36ms to measure open-circuit input voltage (VOC), storing it as a DAC reference. During normal operation, it compares the MPPT pin voltage (set by external resistor divider) against 10% of VOC; if the former falls below, it reduces charge current to maintain VIN at the programmed VMP level - all without MCU involvement.

What is the recommended PROG resistor value for 400mA charge current with the LTC4121IUD-4.2#PBF?

A 3.01kΩ 1% resistor from PROG to GND sets the nominal 400mA charge current for the LTC4121IUD-4.2#PBF, based on the formula ICHG = 988 × 1.227V / RPROG. Electrical characteristics confirm 383–421mA over temperature and line conditions, meeting the 400mA specification with margin for production tolerance.

Does the LTC4121IUD-4.2#PBF support NTC temperature monitoring?

Yes, the LTC4121IUD-4.2#PBF supports NTC thermistor-based temperature qualification via the NTC pin. It detects cold faults when VNTC falls below 74% of INTVCC and hot faults when VNTC rises above 36.5% of INTVCC, entering standby mode until the battery returns to safe temperature - complying with JEITA charging profiles for Li-Ion cells.

What package type and thermal specifications apply to the LTC4121IUD-4.2#PBF?

The LTC4121IUD-4.2#PBF uses a 16-lead 3mm × 3mm plastic QFN with exposed thermal pad (Pin 17 = GND). Its thermal resistance is θJA = 54°C/W when properly soldered to a 1-in² 2-oz copper pad, enabling reliable operation up to 125°C junction temperature in compact industrial enclosures.