Analog Devices Inc. DC879A-A

Overview

LTC3525D-3.3 from Analog Devices (formerly Linear Technology) is a micropower synchronous step-up DC/DC converter optimized for single-cell alkaline/NiMH or Li-Ion battery-powered systems. It starts up from 0.85V, delivers fixed 3.3V output with pass-through mode in shutdown, supports up to 140mA load at 1.8V input, and achieves up to 95% efficiency. It serves as a compact, high-efficiency replacement for charge pumps in portable medical and instrumentation devices.

For engineers reviewing the LTC3525D-3.3 datasheet, LTC3525D-3.3 pinout, LTC3525D-3.3 application, or LTC3525D-3.3 equivalent, key selection criteria include ultralow 7µA quiescent current, 0.85V startup capability, SC70-6 package footprint, pass-through mode behavior, and synchronous rectification enabling >90% efficiency at light loads.

Technical Context

The LTC3525D-3.3 employs Burst Mode® operation with adaptive peak/valley inductor current control: peak switch current scales from 150mA (light load) to 400mA (heavy load), while valley current adjusts to maintain stable ripple and switching frequency. Its proprietary start-up oscillator enables operation below 1V input, and internal N-channel (0.5Ω) and P-channel (0.8Ω) MOSFETs eliminate external diode requirements.

During shutdown, SHDN < 0.4V activates the internal P-channel MOSFET, connecting VIN to VOUT through the inductor-enabling true pass-through mode. In normal operation, synchronous rectification engages only when VOUT exceeds VIN by ≥0.2V; below that threshold, efficiency drops due to follower-mode P-channel conduction.

Key Specifications

Pinout & Package

Package: 6-Lead Plastic SC70 (EIAJ SC-70, JEDEC MO-203 AB), 2.2mm × 1.35mm × 1.0mm body, 0.65mm pitch, 1mm max height.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar synchronous step-up converter applications.

Compared with LTC3525-3.3, the LTC3525D-3.3 uniquely provides VIN-to-VOUT pass-through in shutdown - a functional distinction critical for systems requiring uninterrupted power rail behavior. Against LTC3429B, it trades higher peak current and 5V flexibility for 7µA IQ and guaranteed 3.3V accuracy, making it superior for long-life, single-rail portable instrumentation.

Availability

LTC3525D-3.3 is available at Aetrix Electronics and suitable for glucose meters, portable audio players, handheld test instruments, and digital cameras requiring stable component supply with consistent parametric performance and long-term lifecycle support.

Supply support for LTC3525D-3.3 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 and power management ICs with rigorous qualification and long-term product support.

The LTC3525D-3.3 belongs to Linear's micropower synchronous boost converter family, designed specifically for battery-powered portable electronics demanding ultra-low quiescent current, minimal footprint, and robust low-voltage startup capability.

FAQ

What is the minimum input voltage required for LTC3525D-3.3 to start switching?

The LTC3525D-3.3 requires a minimum input voltage of 0.85V to initiate startup. Once regulation begins, it can sustain operation down to 0.5V depending on load current. This enables reliable operation from aging single-cell alkaline or NiMH batteries, and the internal start-up oscillator ensures consistent turn-on even under high-impedance source conditions. The LTC3525D-3.3 achieves this without external assist circuitry.

How does pass-through mode work in LTC3525D-3.3 during shutdown?

In shutdown, when SHDN is pulled below 0.4V, the LTC3525D-3.3 turns on its internal P-channel MOSFET, creating a low-resistance path from VIN to VOUT through the external inductor. This pass-through mode maintains output voltage continuity without external components. Unlike output disconnect variants, the LTC3525D-3.3 does not isolate VOUT - it actively routes VIN to the output rail, preserving system power integrity during sleep states.

Can LTC3525D-3.3 operate with input voltage higher than 3.3V?

Yes - the LTC3525D-3.3 supports VIN from 0.5V to 4.5V. When VIN ≥ VOUT (e.g., 3.6V), the device enters pass-through-like operation: the synchronous rectifier disables, and the P-channel MOSFET conducts as a follower, delivering VIN to VOUT with reduced efficiency and lower output current capability. This behavior is inherent to the LTC3525D-3.3 architecture and does not damage the IC, though efficiency drops to ~70% in this region.

What external components are required for basic LTC3525D-3.3 operation?

The LTC3525D-3.3 requires only three external components: a 10µH inductor (e.g., Murata LQH32CN100K53), a 10µF ceramic output capacitor (X5R/X7R), and a 1µF ceramic input bypass capacitor. No feedback resistors, compensation networks, or Schottky diodes are needed. This minimal BOM reduces cost, board area, and design complexity - a defining feature of the LTC3525D-3.3 architecture.

Is LTC3525D-3.3 pin-compatible with other members of the LTC3525 family?

No - the LTC3525D-3.3 shares the same SC70-6 package and pinout with LTC3525-3.3 and LTC3525-3, but functional differences exist. While pin assignments (SHDN, GND, VIN, VOUT, GND, SW) match, the shutdown behavior differs: LTC3525D-3.3 enables pass-through mode, whereas LTC3525-3.3 disconnects VOUT. Substituting them without verifying system-level shutdown requirements may cause unintended rail behavior. Always validate against the specific LTC3525D-3.3 datasheet.