Analog Devices Inc. LTC4121IUD-4.2#TRPBF

Overview

LTC4121IUD-4.2#TRPBF 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 safety timer termination, auto-recharge, and bad-battery fault detection for solar-powered industrial sensors.

For engineers reviewing the LTC4121IUD-4.2#TRPBF datasheet, LTC4121IUD-4.2#TRPBF pinout, LTC4121IUD-4.2#TRPBF application, or LTC4121IUD-4.2#TRPBF equivalent, key selection criteria include its fixed 4.2V float accuracy (±1.2%), programmable 50–400mA charge current via PROG resistor, integrated MPPT sampling at 30s intervals, thermal shutdown behavior, and QFN-16 (3mm × 3mm) package compatibility with high-density PCB layouts.

Technical Context

The LTC4121IUD-4.2#TRPBF implements a synchronous buck topology with internal 0.8Ω top/0.5Ω bottom MOSFETs, 750kHz or 1.5MHz selectable switching frequency, and precise 4.200V ±0.012V regulated float voltage referenced to BATSNS. Its MPPT loop samples open-circuit input voltage every 28 seconds using a 36ms pulse-width pause, compares it against a user-programmed fraction (via external resistive divider on MPPT pin), and dynamically reduces charge current to maintain VIN ≥ VMP = 0.1 × VOC.

It features dual-stage battery preconditioning: linear low-battery charging (6–16mA) below 2.21V, followed by switch-mode trickle charge above that threshold; end-of-charge detection at 10% of programmed current; and NTC monitoring with cold (73–75% INTVCC) and hot (35.5–37.5% INTVCC) fault thresholds. The FAULT and CHRG pins provide open-drain status signaling with 2mA sink capability.

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 performance (θJA = 54°C/W) and electrical integrity.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LTC4121IUD-4.2#TRPBF, LTC4125IUF#TRPBF offers broader battery voltage flexibility and power-path control but requires redesign for fixed 4.2V use, while BQ24650RGER provides higher current at lower cost but adds complexity and lacks integrated MPPT-making LTC4121IUD-4.2#TRPBF optimal for compact, solar-optimized Li-Ion charging.

Availability

LTC4121IUD-4.2#TRPBF is available at Aetrix Electronics and suitable for solar-powered remote sensors, industrial handheld instruments, and military-grade portable radios requiring stable component supply, long-term lifecycle support, and guaranteed parametric performance across –40°C to 125°C.

Supply support for LTC4121IUD-4.2#TRPBF 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, Inc. (ADI) is a global semiconductor leader specializing in high-performance analog, mixed-signal, and digital signal processing technologies for precision instrumentation, power management, and industrial systems.

The LTC4121 product line was designed by Linear Technology (acquired by ADI in 2017) specifically for high-efficiency, wide-input battery charging in energy-harvesting and harsh-environment applications-emphasizing MPPT, thermal safety, and minimal external component count.

FAQ

What is the exact float voltage tolerance of the LTC4121IUD-4.2#TRPBF over temperature?

The LTC4121IUD-4.2#TRPBF guarantees a fixed float voltage of 4.200V with ±0.012V (±0.29%) initial accuracy at 25°C, and ±0.031V (±0.74%) over the full –40°C to 125°C junction temperature range, as confirmed in the Electrical Characteristics table under VFLOAT parameter. This ensures compliance with JEITA and IEC 62133 standards for Li-Ion charging.

Can the LTC4121IUD-4.2#TRPBF be used without an NTC thermistor?

Yes-the LTC4121IUD-4.2#TRPBF supports NTC-disabled operation: tie the NTC pin directly to GND and omit the INTVCC-to-NTC bias resistor. In this configuration, thermal qualification is disabled, and the device proceeds with normal charging. No additional configuration or register setting is required.

How does the MPPT function behave when the input source is disconnected or drops below 4.4V?

When VIN falls below 4.4V or drops below VBAT + 160mV, the LTC4121IUD-4.2#TRPBF engages differential undervoltage lockout (DUVLO), disabling charging and entering shutdown mode. MPPT sampling pauses entirely until VIN recovers above the threshold, preventing erroneous regulation attempts during brownout or source removal.

What is the maximum recommended inductor value for the LTC4121IUD-4.2#TRPBF at 1.5MHz switching frequency?

For 1.5MHz operation (FREQ = INTVCC), Analog Devices recommends inductors between 1.5µH and 4.7µH. A 2.2µH shielded power inductor with ≥1.5A saturation current (e.g., TDK SLF7045T-2R2N1R5) is optimal-ensuring continuous conduction mode at 400mA while limiting peak current to <1.25A per the IPEAK specification.

Does the LTC4121IUD-4.2#TRPBF support automatic recharge, and what triggers it?

Yes-the LTC4121IUD-4.2#TRPBF initiates automatic recharge when the battery voltage (measured at BATSNS) drops by 2.2% below the 4.2V float voltage, i.e., to ≈4.108V. This threshold is fixed and unadjustable, ensuring consistent reconditioning without firmware or external timing components.