Analog Devices Inc. LTC1731ES8-4.1#PBF

Overview

LTC1731ES8-4.1#PBF from Analog Devices (formerly Linear Technology) is a single-cell lithium-ion linear battery charger controller with internal 4.1V float voltage regulation, ±1% output accuracy, 5% charge current programming accuracy via external R_PROG/R_SENSE, and C/10 end-of-charge detection. It operates from 4.5V to 12V input, supports automatic trickle charge for cells below 2.457V, and enters 7µA sleep mode when input is removed - used in handheld computers and charging docks.

For engineers reviewing the LTC1731ES8-4.1#PBF datasheet, LTC1731ES8-4.1#PBF pinout, LTC1731ES8-4.1#PBF application, or LTC1731ES8-4.1#PBF equivalent, key selection criteria include float voltage tolerance (±1%), programmable timer termination, CHRG open-drain status signaling, thermal shutdown behavior, and compatibility with P-channel MOSFET or high-gain PNP pass devices.

Technical Context

The LTC1731ES8-4.1#PBF implements a dual-loop linear control architecture: a current amplifier (CA) servoing the DRV pin to regulate IBAT via external R_SENSE, and a voltage amplifier (VA) reducing charge current as BAT approaches 4.1V. Trickle charge initiates at V_BAT < 2.457V and delivers 10% of programmed current until threshold is exceeded.

Charge termination uses either C/10 detection (internal comparator monitoring IBAT decay) or programmable timer (CTIMER-based, t_TIMER = 3h × C_TIMER/0.1µF). The PROG pin enables shutdown via floating (2.5µA internal pull-up), while TIMER pin shorted to GND disables C/10 and timer functions - enabling constant-current-only operation for NiMH/NiCd.

Key Specifications

Pinout & Package

Package: 8-lead plastic SO (Small Outline, narrow 0.150") - RoHS-compliant, surface-mount, footprint compatible with industry-standard SOIC-8 layouts.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LTC1731ES8-4.2#PBF, the LTC1731ES8-4.1#PBF provides tighter voltage margin for aging or high-temperature Li-ion cells, while LTC4053EDD-4.2#TRMPBF trades configurability for integration and smaller footprint - making it unsuitable as a direct replacement without layout and firmware changes.

Availability

LTC1731ES8-4.1#PBF is available at Aetrix Electronics and suitable for handheld computers, charging docks, and cellular phones requiring stable component supply, long-lifecycle support, and guaranteed RoHS compliance.

Supply support for LTC1731ES8-4.1#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 full technical and manufacturing continuity for legacy Linear products including the LTC1731 series.

The LTC1731 product line was designed specifically for cost-sensitive, microcontroller-free Li-ion charging in portable consumer electronics - emphasizing simplicity, reliability, and minimal external component count.

FAQ

What is the exact float voltage setpoint for LTC1731ES8-4.1#PBF and how tightly is it controlled?

The LTC1731ES8-4.1#PBF has a factory-trimmed internal float voltage of 4.1V with a maximum deviation of ±1% (4.059V to 4.141V) across the full operating temperature range of –40°C to 85°C. This specification is guaranteed by design and confirmed through characterization - not just typical - ensuring compliance with conservative Li-ion cell voltage limits under worst-case conditions.

Can LTC1731ES8-4.1#PBF be used to charge NiMH batteries, and if so, what modifications are required?

Yes, LTC1731ES8-4.1#PBF can charge NiMH batteries by connecting the TIMER pin directly to VCC, which disables the constant-voltage loop and timer, forcing constant-current-only operation. External termination (e.g., –ΔV detection or temperature cutoff) must be implemented separately, as the LTC1731ES8-4.1#PBF does not provide NiMH-specific termination logic.

What is the recommended external pass device type for LTC1731ES8-4.1#PBF, and why is the DRV pin clamped?

The LTC1731ES8-4.1#PBF is optimized for P-channel MOSFETs, with the DRV pin internally clamped 6.5V below VCC to protect low V_GS(breakdown) devices (e.g., 8V-rated FETs). For bipolar operation, a high-gain Darlington PNP like ZTX749 is required - standard PNPs introduce >1.6% current error due to CA gain limitations.

How does the CHRG pin indicate charge status, and what are the three distinct states it supports?

The CHRG pin on LTC1731ES8-4.1#PBF provides three states: (1) actively pulled low during constant-current charging, (2) weakly pulled to ~0.8V via 100µA sink at C/10, and (3) high-impedance after timer expiry or shutdown. These states enable simple microprocessor polling using two resistors (2kΩ pull-up, 100kΩ to ground) without additional logic.

What happens to LTC1731ES8-4.1#PBF when the input supply is removed, and how quickly does it enter sleep mode?

When VCC drops below the UVLO threshold (4.1V) or falls within 54mV of VBAT, the LTC1731ES8-4.1#PBF automatically enters sleep mode within microseconds, reducing battery drain current to 7µA typical. In this state, the internal resistor divider disconnects from BAT, DRV goes to VCC, and CHRG becomes high-impedance - preserving battery capacity during storage or intermittent use.