Analog Devices Inc./Maxim Integrated MAX685EEE

Overview

MAX685EEE from Maxim Integrated is a dual-output DC-DC converter designed for powering CCD imaging devices and LCD bias rails. It delivers independently regulated positive output up to +24V and negative output down to −9V, each at up to 10mA, from a +2.7V to +5.5V input. Its single-inductor architecture, integrated power switches, and 30mV_p-p output ripple support compact, low-noise imaging and display subsystems in camcorders and digital cameras.

For engineers reviewing the MAX685EEE datasheet, MAX685EEE pinout, MAX685EEE application, or MAX685EEE equivalent, this device requires attention to its dual-regulation control logic, selectable power-on sequencing (SEQ), POK monitoring, and external clock synchronization capability - all critical for timing-sensitive analog front-end designs.

Technical Context

The MAX685EEE implements two independent PWM current-mode regulators sharing one inductor: one operates as a step-up converter (LXP-driven) for the positive rail, the other as an inverting converter (LXN-driven) for the negative rail. Each regulator cycles alternately at half the oscillator frequency (110kHz or 200kHz nominal), enabling fixed-frequency operation with low EMI.

Regulation relies on internal 1.25V reference (REF), FBP and FBN feedback comparators with thresholds of 1.24V (±3%) and −0.1V respectively, and POK assertion when both outputs reach ≥90% of target. The SEQ pin selects startup order, while SHDN enables 0.1µA shutdown mode with full output disable.

Key Specifications

Pinout & Package

MAX685EEE is packaged in a 16-pin QSOP (0.150" wide, 0.025" lead pitch), with exposed pad not connected internally. Pin functions are electrically validated per Maxim's datasheet revision 1 (June 2003).

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX685EEE, MAX686EEE extends negative output capability and current drive for next-gen imaging sensors, while TPS65131RGTR trades programmability and sequencing for integration and size - making MAX685EEE the optimal choice for mixed CCD/LCD systems requiring design flexibility and rail coordination.

Availability

MAX685EEE is available at Aetrix Electronics and suitable for CCD imaging systems, LCD bias generation, and portable medical sensor designs requiring stable component supply across extended temperature ranges (−40°C to +85°C).

Supply support for MAX685EEE 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 MAX685EEE belongs to Maxim's precision DC-DC converter product line, engineered specifically for low-noise, dual-rail bias generation in imaging and display subsystems where compact size, sequencing control, and ripple performance are critical.

FAQ

What is the maximum negative output voltage achievable with the MAX685EEE?

The MAX685EEE guarantees a minimum negative output of −9V under standard conditions. With external components (charge pump configuration per Figure 4 in the datasheet), it can deliver down to −16V. However, the absolute constraint is that the voltage difference between VDD and VOUT− must not exceed 14.5V - so lower VDD values enable larger magnitude negative outputs. The MAX685EEE datasheet specifies this limit explicitly in Note 1 of the Electrical Characteristics table.

Does the MAX685EEE support independent regulation of both outputs simultaneously?

Yes, the MAX685EEE uses two independent PWM current-mode regulators - one for the positive rail (controlled via FBP) and one for the negative rail (controlled via FBN). Each regulates its respective output against dedicated internal thresholds (1.24V for FBP, −0.1V for FBN), allowing simultaneous, stable operation even with mismatched loads. This dual-loop architecture is confirmed in the Functional Diagram (Figure 1) and Detailed Description section of the MAX685EEE datasheet.

Can the MAX685EEE be synchronized to an external clock, and what is the valid frequency range?

Yes, the MAX685EEE supports external clock synchronization via the SYNC pin. It accepts square-wave inputs from 200kHz to 480kHz. When synchronized, each output switches at half the applied SYNC frequency (e.g., 300kHz SYNC → 150kHz per rail). The internal oscillator operates at 220kHz (SYNC = GND) or 400kHz (SYNC = VDD). This capability is documented in the Electrical Characteristics table and Applications Information section of the MAX685EEE datasheet.

What is the purpose of the SEQ pin on the MAX685EEE, and how does it affect startup behavior?

The SEQ pin on the MAX685EEE controls power-on sequencing order: when SEQ = VDD, the positive output powers up first; when SEQ = GND, the negative output powers up first. During sequencing, the unpowered rail remains disabled until the powered rail reaches ≥90% of regulation. This prevents reverse-bias stress in CCDs and improper LCD gate activation. The behavior is verified in the Start-Up waveforms (Figures 11 and 12) and described in the SEQ and Power OK (POK) subsection of the MAX685EEE datasheet.

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

The POK output on the MAX685EEE is an open-drain indicator that goes high-impedance only when both outputs are within ≥90% of their target voltages. If either output falls below that threshold, POK pulls low (≤0.4V at 2mA sink). During shutdown, POK remains high-impedance. A 100kΩ pull-up to VDD is required. This real-time dual-rail monitoring function is specified in the POK Comparators table and illustrated in the Start-Up and Line-Transient Response waveforms of the MAX685EEE datasheet.