Analog Devices Inc./Maxim Integrated MAX1685EEE

Overview

MAX1685EEE from Maxim Integrated is a high-efficiency, internal-switch, 600kHz PWM step-down DC-DC converter delivering 1A output current from 2.7V–14V input, with preset 3.3V (±1%) or adjustable 1.25V–VIN output. It integrates a 0.24Ω P-channel MOSFET, synchronous rectifier, and 1% accurate 1.25V reference, targeting power management in handheld communications devices.

For engineers reviewing the MAX1685EEE datasheet, MAX1685EEE pinout, MAX1685EEE application, or MAX1685EEE equivalent, this page delivers verified technical context, real-world operating modes (PWM/normal/low-power/shutdown), package mapping to 16-QSOP, and validated alternative options for portable power supply design.

Technical Context

The MAX1685EEE uses oscillator-triggered current-mode control with minimum on-time of 220ns and maximum on-time of 2/f_OSC, enabling true 100% duty-cycle operation for ultra-low dropout. Its dual-mode feedback (FB grounded for 3.3V fixed; resistor-divider for adjustable output) interfaces directly with the 1.25V reference and supports external synchronization via SYNC/PWM pin.

It implements five distinct operating modes-fixed-frequency PWM (600kHz), synchronized PWM, normal (PFM at light load), low-power (standby), and shutdown-with mode selection governed by STBY and SYNC/PWM logic levels. Internal regulators supply CVL (3V/5mA) and CVH (−4.6V w.r.t. IN), while BOOT connection to VOUT enables quiescent current reduction in normal/low-power modes.

Key Specifications

Pinout & Package

MAX1685EEE is housed in a 16-pin QSOP (Quad Small Outline Package) with 0.65mm pitch, optimized for space-constrained portable designs. Thermal performance supports continuous 1A operation at −40°C to +85°C ambient.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX1685EEE, MAX1692EUA+ trades 14V input flexibility and auxiliary CVL capability for smaller footprint and higher current, while TPS62231DRVR sacrifices input range and feature set for extreme miniaturization and higher switching frequency - making MAX1685EEE optimal for mid-power, multi-rail, battery-plus-adapter systems.

Availability

MAX1685EEE is available at Aetrix Electronics and suitable for cellular phone power supply, two-way radio baseband core, handheld terminal application processor, and portable PDA LCD backlight bias applications requiring stable component supply across extended product lifecycles.

Supply support for MAX1685EEE 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

Maxim Integrated (now part of Analog Devices) is a semiconductor company specializing in high-performance analog, mixed-signal, and power management ICs for demanding industrial, automotive, and portable applications.

The MAX1684/MAX1685 product line was designed specifically for efficient, low-noise DC-DC conversion in battery-powered handheld communication devices, emphasizing wide input range, multiple operating modes, and integration of auxiliary supplies.

FAQ

What is the maximum input voltage rating for MAX1685EEE?

The MAX1685EEE has an absolute maximum input voltage rating of 15V, with recommended continuous operation from 2.7V to 14V. Exceeding 15V may cause permanent damage. The device's wide input range supports both dual Li+ battery packs (up to ~8.4V fully charged) and wall adapters (up to 14V), making MAX1685EEE suitable for hybrid power architectures.

How does the MAX1685EEE achieve 100% duty-cycle operation?

The MAX1685EEE achieves 100% duty cycle by holding its internal P-channel MOSFET continuously on when input voltage approaches output voltage - eliminating switching losses and minimizing dropout. This behavior is enabled by its current-mode control architecture and absence of minimum off-time constraint. At 1A load, dropout voltage is approximately 350mV (I_OUT × R_DS(ON)), ensuring regulation even with deeply discharged batteries.

Can MAX1685EEE be synchronized to an external clock, and what is the acceptable frequency range?

Yes, MAX1685EEE supports external clock synchronization via the SYNC/PWM pin. When driven with a TTL-level 50% duty-cycle square wave, it locks to frequencies between 520kHz and 680kHz - covering its nominal 600kHz switching frequency with ±13% margin. This capability prevents beat frequencies in systems with multiple switching regulators, such as cellular handsets with separate RF and baseband power domains.

What is the purpose of the CVL pin on MAX1685EEE, and how is it used?

The CVL pin on MAX1685EEE provides a regulated 3V output capable of sourcing up to 5mA. It powers internal low-voltage circuitry and can supply external logic, level shifters, or bias networks. CVL is active in normal and low-power modes but disabled in shutdown. In low-power mode, CVL also serves as the reference for STBY pin logic - connecting STBY to AGND forces standby operation independent of SYNC/PWM state.

How does the BOOT pin function in MAX1685EEE, and when should it be connected to AGND instead of VOUT?

The BOOT pin on MAX1685EEE enables internal bootstrap operation: when connected to VOUT (≤5.5V), it reduces quiescent current by powering internal circuitry from the output rail instead of VIN. If VOUT exceeds 5.5V, BOOT must be connected to AGND to prevent overvoltage stress on the internal CVL regulator - in that case, CVL remains regulated at 3V from the VH supply, maintaining safe operation but with higher input quiescent current.