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 up to 1A output current from 2.7V–14V input, with preset 3.3V (±1%) or adjustable 1.25V–VIN output. It integrates a P-channel high-side switch (0.24Ω), 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, key selection criteria include its 600kHz switching frequency enabling compact external components, 100% duty-cycle dropout operation, four-mode control (PWM/normal/low-power/shutdown), and auxiliary 3V/5mA CVL output for biasing peripheral logic.

Technical Context

The MAX1685EEE+ employs current-mode PWM control with oscillator-triggered minimum/maximum on-time regulation, supporting fixed-frequency operation at 600kHz or synchronization to an external clock. Its dual-mode feedback (FB pin grounded for 3.3V or resistor-divider for adjustable output) interfaces directly with the 1.25V reference and integrator compensation network (CC pin).

It features integrated low-voltage regulators: VH supplies –4.6V (w.r.t. IN) to the P-channel gate driver, while VL delivers 3V/5mA at CVL for internal circuitry and external loads. Bootstrap operation (BOOT connected to VOUT) reduces quiescent current by sourcing internal bias from the output voltage when VOUT ≤ 5.5V.

Key Specifications

Pinout & Package

MAX1685EEE+ is housed in a 16-pin QSOP package (5.3mm × 10.2mm, 0.65mm pitch), optimized for space-constrained portable designs. Thermal pad is not present; power dissipation is managed via PGND and LX thermal paths.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX1684EEE+, the MAX1685EEE+ trades slightly higher gate-drive losses for 50% smaller magnetics and tighter layout; versus MAX1692EUA+, it provides 67% higher output current, 2.5× wider input range, and auxiliary CVL bias-making it the sole fit for dual-cell Li+ powered handhelds demanding 1A at 3.3V.

Availability

MAX1685EEE+ is available at Aetrix Electronics and suitable for cellular handsets, two-way radios, and PDA power management requiring stable component supply, long-lifecycle availability, and consistent parametric performance across production batches.

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 industrial, automotive, and portable applications.

The MAX1684/MAX1685 product line was designed specifically for low-noise, high-efficiency power conversion in battery-powered communication devices-emphasizing wide input range, multiple operating modes, and integrated auxiliary functions to minimize external components.

FAQ

What output voltage options does the MAX1685EEE+ support?

The MAX1685EEE+ supports two output configurations: a factory-preset 3.3V output (±1%) achieved by grounding the FB pin, or an externally adjustable output from 1.25V to VIN using a resistor divider connected to FB. The 1.25V internal reference (REF pin) enables precise adjustment without external references, and the device maintains ±1% accuracy over temperature and load for both modes.

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

The MAX1685EEE+ achieves 100% duty-cycle operation by holding its internal P-channel high-side switch continuously on when input voltage approaches output voltage. This minimizes dropout to I_OUT × R_DS(on) (≈240mV at 1A), allowing regulation even as dual Li+ cells discharge below 3.3V. The feature is automatic and requires no external circuitry-enabled inherently by the current-mode control architecture and zero-crossing detection.

What is the purpose of the CVL pin on the MAX1685EEE+?

The CVL pin on the MAX1685EEE+ provides a regulated 3V output capable of sourcing up to 5mA. It powers internal low-voltage circuitry (including the N-channel synchronous rectifier driver) and can also supply external logic such as microcontroller I/O banks or level shifters. CVL is disabled during shutdown, and its voltage remains stable across input variations (2.7V–14V) due to internal regulation-eliminating the need for a separate LDO in many portable designs.

Can the MAX1685EEE+ be synchronized to an external clock?

Yes, the MAX1685EEE+ can be synchronized to an external clock via the SYNC/PWM pin. When driven with a TTL-level square wave (480–700kHz), the internal oscillator locks to the external frequency, eliminating beat frequencies and simplifying EMI filtering in multi-rail systems. In synchronized mode, the device retains all four operating modes (PWM/normal/low-power/shutdown), and the external clock replaces the internal 600kHz oscillator without affecting regulation accuracy or transient response.

What are the thermal limitations of the MAX1685EEE+ in a 16-QSOP package?

The MAX1685EEE+ in 16-QSOP has a maximum continuous power dissipation of 667mW at +70°C ambient, derating by 8.3mW/°C above that temperature. Its junction-to-ambient thermal resistance (θ_JA) is approximately 150°C/W. To maintain reliability, PCB layout must prioritize thermal relief: use wide copper pours connected to PGND and LX pins, avoid thermal isolation of the package, and ensure ambient temperature stays below +85°C. Thermal shutdown activates at +160°C (with hysteresis) but is disabled in low-power mode to preserve ultra-low quiescent current.