Analog Devices Inc./Maxim Integrated MAX1855EEG+

Overview

MAX1855EEG+ from Maxim Integrated is a high-speed, synchronous step-down controller with integrated voltage positioning, designed specifically for CPU core power supplies in notebook computers. It delivers 0.600V–1.75V dynamically adjustable output via 5-bit DAC, supports 2V–28V input, achieves ±1% DC output accuracy, and features Quick-PWM™ architecture enabling 100ns load transient response. It drives large synchronous-rectifier MOSFETs in single-stage (battery-to-V_CORE) or two-stage (+5V-to-V_CORE) converter topologies.

For engineers reviewing the MAX1855EEG+ datasheet, MAX1855EEG+ pinout, MAX1855EEG+ application, or MAX1855EEG+ equivalent, this page provides verified technical context, validated pin functions, confirmed voltage-positioning behavior, real-world efficiency curves at 400kHz/550kHz, and direct alternative part comparisons - all grounded in the official 19-1758 Rev 0 datasheet and Maxim's published operating characteristics.

Technical Context

The MAX1855EEG+ implements Maxim's proprietary Quick-PWM™ constant-on-time control scheme, delivering stable switching frequency (200/300/400/550kHz selectable via TON pin) while maintaining ultra-fast transient response. Its voltage-positioning loop uses VPS input with 0.153–0.197%/mV gain to modulate output setpoint based on sensed current, reducing full-load dissipation and minimizing required output capacitance.

It integrates dual gate drivers: DH (1.3–5Ω high-side pull-up) and DL (0.5–1.7Ω low-side pull-down), supporting external N-channel MOSFETs. Protection includes overvoltage fault (1.97–2.03V at FB), undervoltage foldback (35–45% drop), thermal shutdown (150°C), and programmable current limiting (adjustable 40–240mV threshold via ILIM).

Key Specifications

Pinout & Package

MAX1855EEG+ is housed in a 24-pin QSOP package (body width 0.154", lead pitch 0.025") with exposed pad for thermal enhancement. Pin functions are validated per Maxim's official pin description table (Rev 0, p.12–13).

Key Features

Applications

Equivalent & Alternatives

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

Compared with MAX1716EEG+ and MAX1854EEG+, the MAX1855EEG+ uniquely supports the lowest 0.600V output (critical for modern low-voltage cores) and includes factory-trimmed overvoltage protection - making it the only choice for designs requiring both sub-0.7V operation and hardware-level OVP safety.

Availability

MAX1855EEG+ is available at Aetrix Electronics and suitable for notebook computers, docking stations, CPU core supply systems, and portable industrial controllers requiring stable component supply, long-term lifecycle support, and guaranteed -40°C to +85°C operation.

Supply support for MAX1855EEG+ 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 computing, communications, and industrial markets.

The MAX1716/MAX1854/MAX1855 product line was engineered specifically for voltage-positioned CPU core power supplies in mobile computing platforms, addressing stringent requirements for fast transient response, high DC accuracy, and multi-frequency adaptability.

FAQ

What is the minimum output voltage supported by the MAX1855EEG+?

The MAX1855EEG+ supports a minimum output voltage of 0.600V, as specified in the "Features" section and confirmed in the Electrical Characteristics table (DAC codes from 0.6V to 1.3V). This 0.6V capability enables compatibility with advanced low-voltage CPU cores requiring deep voltage scaling, unlike the MAX1716EEG+ (0.925V min) or MAX1854EEG+ (0.925V min).

Does the MAX1855EEG+ include overvoltage protection, and how is it implemented?

Yes, the MAX1855EEG+ includes dedicated overvoltage protection with a trip threshold of 1.97–2.03V measured at the FB pin, as documented in the Electrical Characteristics table (p.3, "Output Overvoltage Fault Threshold"). The fault propagates within 1.5µs and forces VGATE low. This feature is absent in the MAX1854EEG+ and differs from the MAX1716EEG+'s 1.8–2.0V threshold.

How does the voltage-positioning function work on the MAX1855EEG+?

The MAX1855EEG+ implements voltage positioning via its VPS pin, which accepts a current-sense signal (typically from CS through a 1kΩ resistor). With a gain of 0.153–0.197%/mV, VPS modulates the FB reference to create a controlled output droop proportional to load current - reducing full-load power loss and relaxing output capacitor requirements.

What switching frequencies are available on the MAX1855EEG+, and how are they selected?

The MAX1855EEG+ supports four discrete switching frequencies: 200kHz (TON = VCC), 300kHz (TON = open), 400kHz (TON = REF), and 550kHz (TON = GND). These are selected by hardwiring the TON pin to specific voltage levels, as defined in the Electrical Characteristics table (p.4, "TON Input Levels") and Typical Operating Characteristics (p.8, MAX1716-13/14).

Can the MAX1855EEG+ drive large MOSFETs, and what are its gate-driver specifications?

Yes, the MAX1855EEG+ is designed to drive large synchronous-rectifier MOSFETs. Its DH driver has 1.3–5Ω on-resistance (pull-up) and supports 1A source/sink current; DL driver has 0.5–1.7Ω on-resistance (pull-down) and delivers 3A sink/1A source current - enabling robust control of high-current power stages as validated in Circuit #1 (18A load, IRF7811/FDS7764A).