Analog Devices Inc. LTC4425IDD#PBF

Overview

LTC4425IDD#PBF from Analog Devices (formerly Linear Technology) is a linear supercapacitor charger with integrated ideal diode, active cell balancing, and V/I monitoring - designed to charge 2-cell series supercap stacks from Li-Ion, USB, or 2.7V–5.5V current-limited sources. It delivers up to 2A peak charge current, features 50mΩ ideal diode on-resistance, programmable 4.9V/5.4V top-off clamping, and operates with only 20µA quiescent current in active mode. It is used in power-meter backup circuits and portable industrial instruments requiring high peak power with low average consumption.

For engineers reviewing the LTC4425IDD#PBF datasheet, LTC4425IDD#PBF pinout, LTC4425IDD#PBF application, or LTC4425IDD#PBF equivalent, key selection criteria include its dual-mode charging (LDO vs. smart current-profile), internal 2.45V/2.7V per-cell voltage clamping, VMID-based active balancing, PROG-pin current monitoring (1000× scaling), and thermal regulation at 105°C - all in a 3mm × 3mm DFN-12 package with exposed GND pad.

Technical Context

The LTC4425IDD#PBF implements a three-loop control architecture: constant-current, constant-voltage, and constant-temperature regulation. Its ideal diode controller maintains 15mV forward drop and shuts off instantly during reverse voltage conditions. The device supports two distinct operating modes - LDO mode (FB grounded, fixed VOUT set by resistor divider) and normal mode (FB tied to VIN, adaptive charge current based on VIN–VOUT differential).

It integrates an active leakage balancer that drives VMID to exactly VOUT/2 with ±1mA sourcing/sinking capability, eliminating external balancing resistors. Voltage clamping uses pin-selectable 2.45V or 2.7V thresholds per cell, with 50mV hysteresis and shunt transistors that activate before overvoltage, reducing charge current to 10% during clamp operation.

Key Specifications

Pinout & Package

Package: 12-lead 3mm × 3mm plastic DFN with exposed GND pad (Pin 13), rated for –40°C to +125°C operation.

Key Features

Applications

Equivalent & Alternatives

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

Compared with LTC4425EMSE#PBF, the LTC4425IDD#PBF offers superior thermal management via its exposed-pad DFN and supports higher continuous current in space-constrained layouts; versus MAX1759EUB+T, it provides full 2-cell management with integrated balancing and dual-threshold clamping - eliminating design compromises in mission-critical backup systems.

Availability

LTC4425IDD#PBF is available at Aetrix Electronics and suitable for power meter backup circuits, industrial PDA power management, and portable instrumentation requiring stable component supply with guaranteed long-term availability and traceable sourcing.

Supply support for LTC4425IDD#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 LTC4425IDD#PBF belongs to Linear's supercapacitor management IC family, engineered specifically for high-reliability, low-maintenance backup power systems in industrial, energy, and portable test equipment.

FAQ

What is the primary function of the LTC4425IDD#PBF in a 2-cell supercapacitor system?

The LTC4425IDD#PBF serves as a fully integrated supercapacitor charger, ideal diode controller, and active cell balancer for 2-cell series stacks. It charges the stack from sources like Li-Ion batteries or USB, regulates output voltage in LDO mode or tracks VIN in normal mode, enforces per-cell voltage limits via pin-selectable clamps, and maintains voltage balance using its VMID output - all without external balancing resistors. This makes the LTC4425IDD#PBF ideal for compact, maintenance-free backup power designs.

How does the PROG pin on the LTC4425IDD#PBF enable both charge current programming and real-time monitoring?

The PROG pin on the LTC4425IDD#PBF functions as both a programming interface and a current-sense node. A resistor from PROG to GND sets the full-scale charge current (I_CHG = 1000 × 1V/R_PROG). Simultaneously, the voltage on PROG remains proportional to actual charge current at all times (V_PROG = I_CHG × R_PROG/1000), enabling accurate, isolated current telemetry without additional components. This dual role is intrinsic to the LTC4425IDD#PBF's architecture and applies in both LDO and normal operating modes.

Can the LTC4425IDD#PBF be used with a single supercapacitor instead of a 2-cell stack?

No - the LTC4425IDD#PBF is specifically designed for 2-cell series supercapacitor stacks and relies on the VMID pin to sense and balance the midpoint voltage. Its internal clamp circuitry, shunt transistors, and balancing amplifier are all optimized for split-stack operation. Using it with a single supercap would leave VMID unconnected or improperly biased, disabling critical protection and balancing functions. For single-cell applications, consider alternatives like the LTC3225 or MAX1759, which are architected for that topology.

What happens to the LTC4425IDD#PBF when the input voltage (VIN) drops below the output voltage (VOUT)?

When VIN drops below VOUT, the LTC4425IDD#PBF's ideal diode controller immediately turns off the internal PMOS pass device to prevent reverse current flow from the supercap stack back to the failing input source. During this condition, the device continues drawing only 20µA from VOUT (if EN is high), sustaining VMID monitoring and clamp functionality - but the balancer is disabled per datasheet specification. The PFO pin asserts low to signal power fail, and the part remains ready to resume charging once VIN recovers above VOUT by >250mV.

How does thermal regulation work in the LTC4425IDD#PBF, and how is it different from thermal shutdown?

The LTC4425IDD#PBF employs two distinct thermal protections: regulation and shutdown. Thermal regulation activates at ~105°C junction temperature, progressively reducing charge current to maintain TJ ≈ 105°C - allowing continued operation under overload or high ambient conditions. In contrast, thermal shutdown triggers at ~160°C, completely disabling the part until junction temperature falls to ~146°C. Regulation is transparent to system operation (PROG pin still reports scaled current), while shutdown halts all charging and requires manual or automatic EN toggle to recover. Both mechanisms are integral to the LTC4425IDD#PBF's robustness in unventilated enclosures.