Analog Devices Inc./Maxim Integrated MAX685EUE

Overview

MAX685EUE from Maxim Integrated is a dual-output DC-DC converter IC designed for powering CCD imaging devices and LCD bias rails. It delivers independently regulated +24V (up to 10mA) and -9V (up to 10mA) from a single +2.7V to +5.5V input using one inductor, features 30mV_p-p output ripple, fixed-frequency PWM operation at 220kHz/400kHz, and includes power-OK indication and selectable power-on sequencing.

For engineers reviewing the MAX685EUE datasheet, MAX685EUE pinout, MAX685EUE application, or MAX685EUE equivalent, this device is selected for low-noise dual-rail generation in portable imaging and display systems where space-constrained layout, sequencing control, and external clock synchronization are critical design requirements.

Technical Context

The MAX685EUE implements a dual-mode current-mode PWM controller that alternates between step-up and inverting topologies on successive cycles, enabling independent regulation of positive and negative outputs with a shared inductor. Each output uses dedicated feedback comparators (FBP threshold = 1.24V, FBN threshold = –0.1V) and internal error amplifiers to maintain regulation under load.

It integrates P-channel and N-channel MOSFET switches (R_DS(on) = 0.6Ω typical), supports external clock synchronization from 200kHz to 480kHz via SYNC, and provides logic-controlled shutdown (0.1µA quiescent current) with programmable startup order via SEQ. The POK output asserts open-drain high-impedance when both outputs reach ≥90% of target voltage.

Key Specifications

Pinout & Package

The MAX685EUE is housed in a 24-pin Thin QFN package (4mm × 4mm × 0.8mm), thermally enhanced with exposed PGND pad. Pin pitch is 0.5mm; RoHS-compliant and lead-free.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar dual-output DC-DC converter applications.

Compared with MAX686EUE and TPS65131RGTR, the MAX685EUE uniquely balances compact 4mm × 4mm packaging, full sequencing control, external clock synchronization, and verified –9V/+24V capability-making it the preferred choice for high-fidelity CCD imaging and precision LCD bias where timing integrity and noise performance are non-negotiable.

Availability

MAX685EUE is available at Aetrix Electronics and suitable for CCD imaging systems, LCD bias generation, and portable digital camera power management requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for MAX685EUE 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 U.S.-based semiconductor company specializing in high-performance analog, mixed-signal, and power management ICs for industrial, communications, and consumer applications.

The MAX685EUE belongs to Maxim's precision DC-DC converter product line, engineered specifically for low-noise, dual-rail power delivery in imaging and display systems where compact size, sequencing control, and EMI resilience are essential.

FAQ

What is the maximum output voltage range supported by the MAX685EUE?

The MAX685EUE supports a positive output voltage up to +24V and a negative output down to –9V using internal feedback thresholds. With external charge-pump components (as shown in Figure 4 of the datasheet), the MAX685EUE can be configured to deliver up to +45V and down to –16V while maintaining regulation. These extended ranges require additional diodes and capacitors but retain the same core control architecture and pin configuration.

Does the MAX685EUE support external clock synchronization, and what is its valid frequency range?

Yes, the MAX685EUE supports external clock synchronization via the SYNC pin. It accepts an external clock signal between 200kHz and 480kHz. When SYNC is grounded, the device operates at 220kHz; when tied to VDD, it runs at 400kHz. The actual switching frequency at each LX node is half the oscillator or sync frequency, so driving SYNC at 400kHz results in 200kHz switching on LXP and LXN.

How does the SEQ pin affect power-up behavior in the MAX685EUE?

The SEQ pin determines the startup sequence of the MAX685EUE's dual outputs. When SEQ is logic-high (tied to VDD), the positive output powers up first and stabilizes before the negative output begins ramping. When SEQ is logic-low (tied to GND), the negative output powers up first. This sequencing prevents transient stress on CCD sensors and LCD panels by ensuring proper bias ordering during system initialization.

What is the role of the POK output in the MAX685EUE, and how is it used?

The POK (Power-OK) output in the MAX685EUE is an open-drain indicator that signals when both positive and negative outputs have reached ≥90% of their target regulation points. It remains high-impedance during shutdown and transitions to low-impedance (pulling to GND) if either output falls out of regulation. A 100kΩ pull-up resistor to VDD is required; POK sinks up to 2mA and interfaces directly with microcontroller reset or enable logic.

Can the MAX685EUE operate from a single-cell Li-ion battery, and what is its minimum input voltage?

Yes, the MAX685EUE is fully compatible with single-cell Li-ion batteries, supporting an input voltage range from +2.7V to +5.5V. Its undervoltage lockout (UVLO) activates below 2.35V (typical), ensuring reliable start-up even as the battery discharges. At VDD = 3.3V, the MAX685EUE maintains full 10mA output capability and meets all specified ripple, efficiency, and sequencing performance metrics.