Analog Devices Inc. LTC3559EUD#PBF

Overview

LTC3559EUD#PBF from Analog Devices (formerly Linear Technology) is a monolithic linear USB battery charger with dual synchronous buck regulators for single-cell Li-Ion/Polymer systems. It delivers up to 950mA charge current, supports 400mA per buck output at 2.25MHz switching frequency, and integrates NTC-based temperature-qualified charging - ideal for compact handheld devices requiring multiple regulated rails from a USB or AC adapter input.

For engineers reviewing the LTC3559EUD#PBF datasheet, LTC3559EUD#PBF pinout, LTC3559EUD#PBF application, or LTC3559EUD#PBF equivalent, key selection considerations include programmable charge current via PROG resistor, HPWR-selectable 20%/100% current scaling, thermal regulation at ~115°C, Burst Mode®/pulse-skip operation for efficiency vs. noise trade-offs, and integrated bad-battery detection with C/10 termination.

Technical Context

The LTC3559EUD#PBF implements a constant-current/constant-voltage (CC/CV) linear charging algorithm with internal timer termination (4-hour safety window) and automatic recharge when battery voltage falls below V_RECHRG (–100mV relative to float). Trickle charge activates below 2.9V with 10% full-scale current and latches bad-battery state after 0.5 hours if voltage remains low.

Each buck regulator uses internal compensation, operates from BAT/PVIN (3.0V–4.2V), and offers MODE-selectable operation: high-efficiency Burst Mode® (35μA no-load quiescent) or low-noise pulse-skip mode (220μA no-load). Feedback reference is 800mV ±20mV across full temperature range, enabling precise 1.2V and 2.5V outputs with external resistor dividers.

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 (θ_JA = 68°C/W).

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar battery charger + dual buck regulator applications.

Compared with LTC3559EUD-1#PBF, the LTC3559EUD#PBF provides higher float voltage for standard Li-Ion capacity; compared with MAX77818EWJ+T, it offers simpler integration, smaller 3×3mm QFN footprint, and lower cost for applications needing only USB charging + two regulated rails.

Availability

LTC3559EUD#PBF is available at Aetrix Electronics and suitable for MP3 players, portable medical monitors, industrial handheld scanners, and smart remote controls requiring stable component supply, guaranteed long-term availability, and full industrial temperature support.

Supply support for LTC3559EUD#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 legacy of high-performance analog/power ICs with rigorous validation and long-lifecycle support.

The LTC3559 product line was designed specifically for space-constrained portable electronics needing integrated USB-compatible battery charging and efficient dual-output DC/DC conversion - balancing thermal performance, feature completeness, and ease of layout.

FAQ

What is the maximum battery charge current supported by the LTC3559EUD#PBF?

The LTC3559EUD#PBF supports up to 950mA maximum charge current at the BAT pin. This is programmable via the PROG pin resistor and scalable to 20% or 100% of the programmed value using the HPWR pin - enabling compliance with USB 2.0 (100mA) and USB BC1.2 (500mA) specifications. The actual delivered current depends on thermal conditions and simultaneous buck regulator loading.

How does the CHRG pin indicate battery temperature faults on the LTC3559EUD#PBF?

The CHRG pin on the LTC3559EUD#PBF signals an NTC temperature fault by outputting a 35kHz square wave modulated at 1.5Hz with duty cycle alternating between 6.25% and 93.75%. This creates a visible "slow blink" for human indication and provides two distinct duty cycles for MCU-based fault decoding - differentiating it from the 6.1Hz pattern used for bad-battery detection.

Can the LTC3559EUD#PBF operate with separate input sources for the charger and buck regulators?

No - the LTC3559EUD#PBF requires the BAT and PVIN pins to be tied together. The buck regulators draw power directly from the battery node, so their input is inherently coupled to the charger's output. This architecture simplifies power routing but means buck loading reduces net battery charge current; for example, 500mA total BAT current with 200mA buck load yields only 300mA effective charge current.

What is the purpose of the MODE pin on the LTC3559EUD#PBF, and how does it affect efficiency?

The MODE pin on the LTC3559EUD#PBF selects between Burst Mode® operation (MODE = high) and pulse-skip mode (MODE = low) for both buck regulators. Burst Mode® reduces no-load quiescent current to 35μA - maximizing light-load efficiency for battery-powered standby - while pulse-skip mode maintains constant 2.25MHz switching for lower output ripple and EMI, at the cost of higher 220μA quiescent current.

Does the LTC3559EUD#PBF include built-in protection against defective batteries?

Yes - the LTC3559EUD#PBF implements bad-battery detection by monitoring battery voltage during initial charge. If voltage remains below 2.9V for more than 0.5 hours, it latches a fault state, terminates charging, and signals "unresponsive battery" via the CHRG pin's 6.1Hz blink pattern. The latch clears only upon VCC cycle or SUSP pin toggle, preventing automatic retry with failed cells.