Analog Devices Inc. LT1571EGN-2#PBF

Overview

LT1571EGN-2#PBF from Analog Devices (formerly Linear Technology) is a constant-current/constant-voltage PWM battery charger IC optimized for 2-cell Li-Ion (8.2V/8.4V), NiMH, and NiCd batteries. It integrates a 1.5A DC/2A peak NPN power switch, internal 0.1Ω current sense resistor (±5% charge current accuracy), and fixed 200kHz switching frequency. It delivers fast charging in compact cradle or portable instrument designs with flag-based termination signaling.

For engineers reviewing the LT1571EGN-2#PBF datasheet, LT1571EGN-2#PBF pinout, LT1571EGN-2#PBF application, or LT1571EGN-2#PBF equivalent, key selection criteria include its fixed 8.2V/8.4V preset voltage, SELECT-pin voltage selection logic, GND-fused 28-pin SSOP thermal design, and FLAG output behavior tied to 20% charge current threshold detection.

Technical Context

The LT1571EGN-2#PBF implements a current-mode PWM buck topology with dual-loop control: an inner current loop using PROG-pin feedback (IPROG = 500µA/A) and an outer voltage loop via BAT2 pin referencing internal 2.465V ±0.6% reference. Its 200kHz oscillator enables compact magnetics while maintaining >87% efficiency at 1A into 8.4V battery.

It uses a saturating NPN switch driven by BOOST pin (VBOOST ≈ VCC + VBAT), with integrated thermal protection and undervoltage lockout (7V typical). The FLAG pin asserts low when charge current drops to ≤20% of programmed value-confirmed by comparator E6 monitoring IPROG vs IVA-and requires external pull-up for use in Li-Ion termination timing circuits.

Key Specifications

Pinout & Package

LT1571EGN-2#PBF uses a 28-pin narrow plastic SSOP (GN package) with four corner GND pins fused to the die attach paddle for thermal conduction. PCB land pattern must expand these GND pads to serve as heat sink; internal ground plane assumed for θJA = 40°C/W rating.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LTC4000IGN#PBF and BQ24610RGER, LT1571EGN-2#PBF delivers fixed 2-cell Li-Ion charging with lowest component count (no external sense or divider), best thermal performance in SSOP via fused GND paddle, and proven robustness in cradle and portable medical applications.

Availability

LT1571EGN-2#PBF is available at Aetrix Electronics and suitable for smartphone cradle chargers, industrial handheld terminals, medical portable monitors, and wireless test instruments requiring stable component supply and long-term manufacturability.

Supply support for LT1571EGN-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 and maintains full technical support, documentation, and manufacturing continuity for all LT-branded products.

The LT1571 series was designed specifically for compact, high-efficiency constant-current/constant-voltage battery charging in portable electronics-emphasizing integration, thermal reliability, and seamless Li-Ion/NiMH/NiCd compatibility.

FAQ

What is the function of the SELECT pin on the LT1571EGN-2#PBF?

The SELECT pin on the LT1571EGN-2#PBF determines the preset battery voltage: open circuit selects 8.2V, and grounding selects 8.4V. This pin interfaces directly with logic-level signals-no pull-up or pull-down resistors are required. It controls an internal resistor divider connected to the BAT2 pin, enabling quick configuration for dual-cell Li-Ion applications without external components. The LT1571EGN-2#PBF does not support other voltages; for adjustable outputs, the LT1571-1 variant must be used.

How does the FLAG output behave during Li-Ion charge termination with the LT1571EGN-2#PBF?

The FLAG pin on the LT1571EGN-2#PBF is an open-collector output that pulls low when the charge current drops to ≤20% of the programmed value-indicating entry into constant-voltage taper mode. It requires an external pull-up resistor (e.g., 300Ω to VCC) to generate a clean logic signal for microcontroller interrupts or timer activation. The threshold is set internally and confirmed by comparator E6 monitoring the filtered IPROG signal at the CAP pin; no additional components are needed for basic termination signaling in the LT1571EGN-2#PBF.

Can the LT1571EGN-2#PBF charge batteries other than Li-Ion?

Yes, the LT1571EGN-2#PBF supports NiMH and NiCd batteries in addition to Li-Ion. Its constant-current regulation and wide input range (8V–26V) accommodate various chemistries. For NiMH/NiCd, the fixed 8.2V/8.4V output serves as a safe upper limit, and the FLAG signal can be repurposed for temperature-based or timed termination. Unlike Li-Ion, NiMH/NiCd do not require precise voltage regulation, so the LT1571EGN-2#PBF's accuracy remains beneficial for current control and thermal management across all supported chemistries.

What thermal design considerations apply to the LT1571EGN-2#PBF in high-current operation?

The LT1571EGN-2#PBF uses a 28-pin SSOP (GN) package with four corner GND pins fused to the internal die attach paddle. To achieve the specified θJA = 40°C/W, these GND pins must connect to expanded PCB copper areas acting as heat spreaders-ideally tied to an internal ground plane. At 1.5A charge current and 8.4V battery, thermal calculations confirm junction temperature stays below 125°C up to 60°C ambient. Without proper GND pad layout, thermal resistance degrades significantly, risking premature thermal shutdown or reduced lifetime.

Is the LT1571EGN-2#PBF RoHS compliant and lead-free?

Yes, the LT1571EGN-2#PBF is RoHS compliant and lead-free. The "#PBF" suffix explicitly denotes lead-free packaging per Analog Devices' standard nomenclature. It meets JEDEC J-STD-020 moisture sensitivity level 3 and is qualified for reflow soldering up to 260°C peak temperature. The GN package uses matte tin plating over copper leadframe, and all internal die materials comply with EU RoHS Directive 2011/65/EU and China RoHS II requirements. Full compliance documentation is available through Analog Devices' product page for LT1571EGN-2#PBF.