Analog Devices Inc./Maxim Integrated MAX42405AFOA+

Overview

MAX42405AFOA+ from Analog Devices is a fully integrated 36V, 5A synchronous buck converter with internal high-side and low-side MOSFETs, fixed 400kHz switching frequency, programmable 0.8V–12V output voltage, and 20μA no-load quiescent current-designed for industrial point-of-load regulation in space-constrained 24V/36V systems.

For engineers reviewing the MAX42405AFOA+ datasheet, MAX42405AFOA+ pinout, MAX42405AFOA+ application, or MAX42405AFOA+ equivalent, key selection considerations include its FC2QFN-17 package thermal performance (θJA = 29°C/W on 4-layer board), dropout operation up to 96% duty cycle, PGOOD monitoring, and dual-phase capability via VEA/SYNCOUT pins.

Technical Context

The MAX42405AFOA+ implements average current-mode control with internal slope compensation, enabling stable operation across wide input/output ratios and superior noise immunity in noisy industrial environments. Its architecture supports both forced-PWM (SYNC tied to BIAS) and automatic skip-mode (SYNC grounded), with soft-start ramp times of 2.5ms at 400kHz.

It integrates a 1.8V BIAS linear regulator with switchover logic, a 0.8V reference with ±1.6% feedback accuracy, and robust protection including overtemperature shutdown (175°C), hiccup-mode short-circuit response, and ±3A negative current limit on the low-side FET.

Key Specifications

Pinout & Package

MAX42405AFOA+ uses a 3.5mm × 3.75mm, 17-pin flip-chip quad flat no-lead (FC2QFN) package with symmetrical VIN/PGND layout for optimized EMI performance and thermal conduction through exposed die paddle.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar synchronous buck converter applications.

Compared with MAX42405AFOA+, MAX42406AFOA+ offers higher current headroom with zero layout change, while LM61480RQR trades dual-phase capability and ultra-low IQ for higher switching frequency and simpler control-but requires redesign for multiphase use cases.

Availability

MAX42405AFOA+ is available at Aetrix Electronics and suitable for industrial automation, point-of-load regulation, and distributed DC power systems requiring stable component supply, long-term lifecycle support, and RoHS-compliant packaging.

Supply support for MAX42405AFOA+ 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

Analog Devices is a global leader in high-performance analog, mixed-signal, and digital signal processing semiconductors, serving industrial, automotive, communications, and healthcare markets since 1965.

The MAX42405/MAX42406 family was designed specifically for compact, high-efficiency industrial POL conversion-emphasizing thermal resilience, EMI robustness, and seamless dual-phase scalability in constrained spaces.

FAQ

What is the maximum output current rating for MAX42405AFOA+ under typical industrial conditions?

The MAX42405AFOA+ is rated for 5A continuous output current. This rating is validated under JEDEC 4-layer board conditions (θJA = 29°C/W) with ambient temperature up to +70°C and full derating beyond that point. The device achieves this with integrated 46mΩ high-side and 23mΩ low-side MOSFETs, enabling efficient operation without external switches. Real-world 5A delivery is confirmed across the full 4.5V–36V input range and 0.8V–12V output range.

Does MAX42405AFOA+ support dual-phase operation, and what pins are required?

Yes, MAX42405AFOA+ supports dual-phase operation using the VEA and SYNCOUT pins. In controller mode, SYNCOUT provides a 180° out-of-phase clock signal, and VEA outputs the voltage error amplifier signal. In target mode, VEA accepts that signal to enforce matched current sharing. Both ICs must operate in forced-PWM mode (SYNC tied to BIAS), and separate FB resistor dividers are required per phase. No external phase controller is needed-the MAX42405AFOA+ handles synchronization and current balancing autonomously.

How does the PGOOD function work on MAX42405AFOA+, and what is its threshold accuracy?

The PGOOD pin on MAX42405AFOA+ is an open-drain output that asserts high when the regulated output voltage reaches 92–96% of the target value, with hysteresis of ~2%. It debounces for 100μs (at 400kHz) or 140μs (at 1.5MHz) to prevent false triggering during transients. PGOOD relies on internal comparators monitoring the FB node against a precision 0.8V reference. An external pull-up resistor is mandatory, and the output sinks up to 1mA while low. This enables reliable power sequencing in multi-rail industrial systems.

What is the purpose of the BIAS pin on MAX42405AFOA+, and how should it be decoupled?

The BIAS pin on MAX42405AFOA+ delivers a regulated 1.8V supply for internal circuitry, derived from either SUP (during startup) or OUT (after regulation is established, if VOUT > 2.5V). It must be decoupled with ≥2.2μF ceramic capacitance to PGND, placed adjacent to the pin. This capacitor stabilizes the internal LDO, suppresses switching noise coupling, and ensures reliable gate drive and error amplifier operation. Using less than 2.2μF risks instability, especially during load transients or input voltage dips.

Can MAX42405AFOA+ operate in dropout, and what is its maximum duty cycle?

Yes, MAX42405AFOA+ supports dropout operation with a maximum duty cycle of 96%, allowing regulation when input voltage approaches output voltage (e.g., 24V input → 22.5V output). This is achieved via adaptive gate drive and optimized control loop response. Dropout behavior is verified across temperature and load, with no loss of PGOOD assertion or regulation accuracy. The 96% limit ensures sufficient off-time for low-side FET conduction and inductor current decay-critical for maintaining stability near VIN ≈ VOUT.