Analog Devices Inc./Maxim Integrated MAX685EEE-T

Overview

The MAX685EEE-T from Maxim Integrated is a dual-output (positive and negative) DC-DC converter designed for powering CCD imaging devices and LCD bias supplies. It delivers up to +24V/10mA and −9V/10mA from a +2.7V to +5.5V input using a single inductor, features 30mV_p-p output ripple, fixed-frequency PWM operation at 220kHz or 400kHz, and integrated power switches in a 24-pin 4mm × 4mm Thin QFN package.

For engineers reviewing the MAX685EEE-T datasheet, MAX685EEE-T pinout, MAX685EEE-T application, or MAX685EEE-T equivalent, this device supports low-noise dual-rail generation with selectable power-on sequencing, external clock synchronization (200–480kHz), and a logic-controlled shutdown drawing only 0.1µA - critical for portable CCD and LCD systems requiring tight voltage regulation and compact layout.

Technical Context

The MAX685EEE-T employs current-mode PWM control with independent regulation of positive and negative outputs via alternating step-up and inverting cycles on a shared inductor. Each output uses dedicated feedback comparators (FBP threshold = 1.24V ±3%, FBN threshold = −0.1V) and internal error amplifiers to maintain regulation across load (0–10mA) and line (2.7–5.5V) variations.

Its oscillator operates internally at 220kHz or 400kHz (selected via SYNC pin), or synchronizes externally between 200kHz and 480kHz; actual switching frequency per output is half that value. The POK output signals regulation status (both outputs within 90% of target) with open-drain logic, while SEQ pin selects startup order - negative-first (SEQ = GND) or positive-first (SEQ = VDD).

Key Specifications

Pinout & Package

The MAX685EEE-T is housed in a 24-pin 4mm × 4mm Thin QFN package (TQFN-24) with exposed thermal pad (PGND pins 13, 14, 15, 16, 17). Pin functions are validated per Maxim's official datasheet Rev 1 (6/03) and match the 24-TQFN top-view configuration.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX686EEE-T, the MAX685EEE-T offers tighter integration for standard CCD/LCD rails (±24V/−9V) with built-in sequencing and POK; versus LT3467EDD#TRPBF, it trades higher switching frequency for robust system-level control features essential in imaging applications.

Availability

MAX685EEE-T is available at Aetrix Electronics and suitable for CCD imaging devices, LCD bias supplies, and digital camera power management requiring stable component supply, long-term lifecycle support, and traceable sourcing.

Supply support for MAX685EEE-T 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) designs precision analog, mixed-signal, and power management ICs for industrial, medical, communications, and consumer applications.

The MAX685EEE-T belongs to Maxim's high-efficiency DC-DC converter product line, engineered specifically for low-noise, dual-rail power in portable imaging and display systems where size, regulation accuracy, and sequencing control are critical.

FAQ

What is the maximum output voltage capability of the MAX685EEE-T?

The MAX685EEE-T delivers up to +24V on the positive output and down to −9V on the negative output using its internal architecture and standard external components. With added diodes and capacitors (per Figure 4 in the datasheet), the MAX685EEE-T can be configured to generate up to +45V and down to −16V - though those extended ranges require careful layout and component derating. The absolute maximum voltage ratings (e.g., LXN to GND ≤ +30V) must not be exceeded in either configuration.

Does the MAX685EEE-T support external clock synchronization?

Yes, the MAX685EEE-T supports external clock synchronization via the SYNC pin, accepting input frequencies from 200kHz to 480kHz. When driven externally, the internal oscillator locks to the applied signal, and each output switches at half that frequency - e.g., a 400kHz sync signal results in 200kHz switching per rail. This feature enables EMI reduction in noise-sensitive systems like digital cameras and medical imaging equipment using the MAX685EEE-T.

How does the POK (Power-OK) output function on the MAX685EEE-T?

The POK output on the MAX685EEE-T is an open-drain indicator that goes high-impedance when both the positive and negative outputs are within 90% of their regulated setpoints. If either output falls outside that window, POK pulls low (≤0.4V at 2mA sink). During shutdown, POK remains high-impedance. A 100kΩ pull-up resistor to VDD is required. This behavior allows system microcontrollers to verify stable dual-rail power before enabling downstream CCD or LCD circuitry - a key safety function in the MAX685EEE-T application.

Can the MAX685EEE-T operate from a 3.3V input supply?

Yes, the MAX685EEE-T operates over an input voltage range of +2.7V to +5.5V, fully supporting 3.3V nominal supplies. At 3.3V input, it maintains regulation across its full output range (e.g., +15V/−7.5V) with typical efficiency of ~65–70% at 10mA load per rail. Input dropout is not applicable since it is a boost/inverting topology - the 3.3V input is sufficient to generate both rails, making the MAX685EEE-T ideal for modern low-voltage portable systems.

What package type is used for the MAX685EEE-T?

The MAX685EEE-T uses a 24-pin Thin QFN package measuring 4mm × 4mm × 0.8mm (TQFN-24), with an exposed thermal pad connected to PGND pins (13, 14, 15, 16, 17). This package replaces the older 16-pin QSOP variant (MAX685ETG) and provides superior thermal performance and board-area efficiency - critical for space-constrained CCD and LCD modules where the MAX685EEE-T is deployed.