Analog Devices Inc. LTC3870EUF-1#PBF

Overview

LTC3870EUF-1#PBF from Analog Devices (formerly Linear Technology) is a PolyPhase® step-down slave controller designed for multiphase DC/DC systems operating with the LTC3887-1 master controller. It delivers precise per-phase current regulation across two channels, supports 4.5V–60V input, 0.5V–14V output, and 100kHz–1MHz synchronized switching frequency, enabling high-current power delivery in telecom and industrial base station supplies.

For engineers reviewing the LTC3870EUF-1#PBF datasheet, LTC3870EUF-1#PBF pinout, LTC3870EUF-1#PBF application, or LTC3870EUF-1#PBF equivalent, key selection criteria include phase-shift programmability via PHASMD, dual-channel ITH-based current sharing, ILIM-selectable 50mV/75mV current sense thresholds, and QFN-24 package compatibility with thermal pad grounding requirements.

Technical Context

The LTC3870EUF-1#PBF implements peak current mode control with external synchronization via SYNC pin, using an integrated PLL to lock to master-generated clocks from the LTC3887-1. Its dual PWM outputs drive external gate drivers or DrMOS devices, while independent RUN0/RUN1 enable control and FAULT0/FAULT1 fault response ensure coordinated startup/shutdown and protection across phases.

Current sensing is performed differentially on ISENSE0±/ISENSE1± with programmable range selection via ILIM (GND = 50mV max, INTVCC = 75mV max), and phase alignment is set by PHASMD voltage (GND, 1/3 INTVCC, 2/3 INTVCC, or INTVCC), yielding four discrete channel-to-SYNC phase relationships per channel - e.g., 180°/0° at GND, 90°/270° at INTVCC.

Key Specifications

Pinout & Package

Package: 24-lead (4mm × 4mm) plastic QFN with exposed pad (Pin 25), rated for –40°C to +125°C junction temperature. Exposed pad must be soldered to PCB ground for thermal management and signal integrity.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar multiphase slave controller applications.

Compared with LTC3870IUF-1#PBF, the LTC3870EUF-1#PBF offers identical electrical performance but with design-assured specifications over –40°C to +125°C rather than fully tested guarantees; compared with LTC3870EUF#PBF, it adds PHASMD-controlled phase shifting and full LTC3887-1 feature parity including ITH-based dynamic current sharing.

Availability

LTC3870EUF-1#PBF is available at Aetrix Electronics and suitable for telecom base station power, industrial PLC CPU core supplies, and high-density server VRMs requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for LTC3870EUF-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 product support, documentation, and manufacturing continuity for the LTC portfolio.

The LTC3870EUF-1#PBF belongs to Linear's PolyPhase® digital power system management IC family, engineered specifically to extend master controllers like the LTC3887-1 in high-current, multi-phase DC/DC converter applications.

FAQ

What is the primary function of the LTC3870EUF-1#PBF in a power system?

The LTC3870EUF-1#PBF functions exclusively as a PolyPhase® step-down slave controller, providing per-phase current regulation and synchronized PWM outputs under supervision of a master controller such as the LTC3887-1. It does not regulate output voltage directly; instead, it ensures precise current sharing across phases by responding to ITH voltage commands and phase alignment signals. The LTC3870EUF-1#PBF enables scalable high-current designs without adding I²C complexity or address conflicts.

How does the PHASMD pin affect timing in the LTC3870EUF-1#PBF?

The PHASMD pin on the LTC3870EUF-1#PBF sets the relative phase offset between the external SYNC clock and each PWM output: at GND, PWM0 leads SYNC by 180° and PWM1 aligns with SYNC; at INTVCC, PWM0 leads by 90° and PWM1 by 270°. This programmability allows interleaving up to six phases (with multiple LTC3870EUF-1#PBF and LTC3887-1 units), reducing input capacitor RMS current and improving thermal distribution. The LTC3870EUF-1#PBF implements these offsets using an internal resistor divider and comparator network.

Can the LTC3870EUF-1#PBF operate without a master controller?

No - the LTC3870EUF-1#PBF is not a standalone controller and requires coordination with a compatible master such as the LTC3887-1. It lacks voltage feedback circuitry, error amplifiers, and output voltage programming; its ITH pins must be driven by the master to set per-phase current limits, and its RUN/FAULT/SYNC pins depend on master signals for sequencing and protection. Attempting autonomous operation results in undefined behavior or failure to regulate. The LTC3870EUF-1#PBF is designed solely as a current-regulating extension of the master's control loop.

What are the key differences between the ILIM pin configurations on the LTC3870EUF-1#PBF?

The ILIM pin on the LTC3870EUF-1#PBF selects current sense threshold range: GND sets both channels to 50mV maximum (low range); INTVCC sets both to 75mV (high range); 1/3 INTVCC configures Channel 0 high / Channel 1 low; 2/3 INTVCC or floating configures Channel 0 low / Channel 1 high. These settings must match the MFR_PWM_MODE_3887-1 register bit 7 in the master to prevent current imbalance. The LTC3870EUF-1#PBF uses this 4-level logic to enable asymmetric current scaling across phases for optimized thermal distribution.

How does EXTVCC improve thermal performance in the LTC3870EUF-1#PBF?

EXTVCC on the LTC3870EUF-1#PBF enables an alternate 5V LDO path that powers INTVCC from an external rail (e.g., system 12V) instead of the main VIN supply, reducing power dissipation in the VIN-to-INTVCC LDO. This is active only when EXTVCC > 4.8V and VIN > 6.5V, and improves efficiency by up to 15% in high-input-voltage applications. The LTC3870EUF-1#PBF integrates dedicated overvoltage protection (14V max) and load regulation (±2%) on EXTVCC, making it safe for direct connection to standard intermediate bus rails.