Analog Devices Inc./Maxim Integrated MAX1759EUB+T

Introduction to the MAX1759EUB+T Buck/Boost Charge Pump Regulator

The MAX1759EUB+T, developed by Analog Devices Inc./Maxim Integrated, is a highly integrated buck/boost charge pump switching regulator designed to generate a regulated power rail from challenging battery sources. Carefully engineered for compact, battery-powered devices, the MAX1759EUB+T supports both fixed and adjustable output modes. It efficiently manages the conversion from single-cell lithium-ion batteries or two to three NiMH/alkaline cells to deliver a stable 3.3V fixed or 2.5V–5.5V adjustable output. The device is housed in a small ten-pin μMAX (or MSOP) package, facilitating use in dense portable designs where PCB real estate is at a premium.

Highlighted Specifications of the MAX1759EUB+T

The MAX1759EUB+T stands out for its combination of flexibility, efficiency, and protection. Highlights include:

Dual-output configuration: Selectable fixed 3.3V or adjustable output from 2.5V to 5.5V.

Wide input range: Operates from +1.6V to +5.5V, suitable for direct connection to a single Li+ cell or several NiMH/alkaline cells.

100mA guaranteed continuous output current from 2.5V input with the ability to handle short current peaks up to 200mA.

Ultra-low quiescent current of 50μA (typ), ideal for extending battery lifespan in portable applications.

5MHz operating frequency, allowing small external component size and rapid transient response.

Integrated power-OK (POK) indicator pin, useful for system monitoring and sequencing.

Comprehensive protection: short-circuit, thermal shutdown, and inrush current limiting via built-in soft-start.

Working Principles and System Structure of the MAX1759EUB+T

Central to the MAX1759EUB+T is its innovative charge-pump architecture, which dynamically switches between buck (step-down) and boost (step-up) modes. This dual-mode regulation is automatically handled by internal control logic, which senses both VIN and VOUT to determine the proper conversion mode.

When the input voltage is below the required output, the device operates as a regulated voltage doubler, transferring charge via a flying capacitor. When the input voltage exceeds the output, the controller transitions to a gated switch charge transfer mode to maximize efficiency and maintain regulation even under light loads. Should heavy load conditions prevent effective regulation in step-down mode, the controller can revert to step-up operation as needed.

Key additional features include a shutdown function (reducing supply current to 1μA), undervoltage lockout for safe operation below 1V input, and open-drain POK output for system-level feedback when output regulation fails.

Electrical, Thermal, and Safety Specifications of the MAX1759EUB+T

The MAX1759EUB+T is specified for operation from –40°C to +85°C, making it versatile for harsh or outdoor applications. Absolute maximum ratings, including 6V pin tolerances, safeguard against accidental over-voltage, while internal thermal shutdown engages at 160°C die temperature (with 20°C hysteresis) to prevent overheating during fault conditions.

Short-circuit protection is provided by foldback current limiting, which restricts maximum load under fault to 110mA, ensuring device integrity. Soft-start sequencing is implemented to control inrush current during startup, supporting robust power supply sequencing and enhancing system reliability. The output can be shut off entirely via the SHDN pin, disconnecting the load and reducing system current drain to microamp levels in standby.

Design Recommendations for Integrating the MAX1759EUB+T

When integrating the MAX1759EUB+T into a PCB, attention to passive component selection and board layout is crucial for achieving optimal performance. The device requires only three external ceramic capacitors: input (CIN), flying/transfer (CX), and output (COUT), enabling a highly compact power solution.

Selection of low ESR (≤20mΩ) ceramic capacitors minimizes output ripple and supports high-frequency operation.

CIN and COUT are typically 10μF each, with CX usually 0.33μF. For higher output currents or reduced cost, combinations with tantalum capacitors can be considered.

For adjustable output operation, select resistor divider values to set the FB pin current at approximately 15μA, with feedback resistors close to the device for layout best practices.

Implementing a solid PCB ground plane and keeping all high-frequency current loops short further improves EMI performance and device efficiency.

Common Use Cases for the MAX1759EUB+T

The MAX1759EUB+T is tailored for low-power, space-constrained battery applications such as:

Li-ion powered handheld devices requiring regulated 3.3V rails from a single cell.

Miniature devices and sensor nodes where space is limited and high efficiency is prioritised.

Backup battery boost converters in larger embedded systems, ensuring reliable power switchover and regulation from depleted or varying battery sources.

Any portable equipment that must cope with varying battery voltages while maintaining strict output voltage rails for sensitive IC loads (e.g., microcontrollers, radio modules, or sensors).

Alternative or Substitute Devices for the MAX1759EUB+T

For projects considering alternatives or replacements for the MAX1759EUB+T, engineers might evaluate the following:

Analog Devices/Maxim Integrated MAX1720: A similar charge pump regulator with lower output current specifications, suitable for light-load applications.

Texas Instruments TPS60100: A regulated charge pump with comparable output current and adjustable voltage configuration.

Linear Technology (now Analog Devices) LTC3240: An alternative in a similar category, supporting fixed and adjustable output with extensive protection features.

When selecting an equivalent or replacement, critical considerations include required output current, input voltage range, package dimension, and system compatibility.

Conclusion

The MAX1759EUB+T offers a highly integrated and feature-rich solution for designers of battery-powered systems challenged by variable supply voltages and stringent space or efficiency requirements. Its buck/boost topology ensures reliable output regulation across a broad input range, while its compact μMAX package, robust protection, and minimal external parts streamline both board layout and system integration. For engineers engaged in power supply design or procurement, the MAX1759EUB+T merits strong consideration as a versatile and space-efficient DC-DC charge pump for next-generation portable products.