onsemi FAN53541UCX

Overview

FAN53541UCX from ON Semiconductor is a 2.4 MHz, 5 A synchronous buck regulator in WLCSP-20 package, delivering adjustable output voltage (0.8 V to 90% VIN) from 2.7–5.5 V input. It integrates high-side and low-side MOSFETs (R_DS(ON) = 33 mΩ / 28 mΩ), supports PFM/PWM mode auto-switching, and features power-good (PGOOD), soft-start, UVLO, and thermal shutdown - deployed in DSP power supplies and communication cards.

For engineers reviewing the FAN53541UCX datasheet, pinout, applications, or equivalent options, key selection criteria include its 20-ball WLCSP footprint, 50 µA typical quiescent current in PFM mode, 2.4 MHz fixed-frequency operation with external sync capability, and no-external-compensation design for compact DC/DC solutions.

Technical Context

The FAN53541UCX employs a proprietary synchronous rectification architecture enabling >90% efficiency at 5 A and >80% at 2 mA load. Its nonlinear fixed-frequency PWM modulator maintains stable 2.4 MHz switching across wide VIN (2.7–5.5 V) and IOUT (0–5 A) ranges while decoupling frequency stability from output capacitor ESR.

It operates in continuous conduction mode (CCM) at medium-to-heavy loads and transitions seamlessly to discontinuous conduction mode (DCM) single-pulse PFM at light loads - achieving <3% VOUT disturbance during mode transition and low-output-ripple PFM operation without requiring ceramic capacitor ESR tuning.

Key Specifications

Pinout & Package

Package: 20-ball Wafer-Level Chip-Scale Package (WLCSP), 4×5 array, 0.4 mm pitch, 250 µm solder balls, 1.96 mm × 1.56 mm body size, 586 µm nominal height.

Key Features

Applications

Equivalent & Alternatives

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

Compared with MP2143GQ-Z and TPS62130ARGTR, the FAN53541UCX delivers 5 A in the smallest footprint (1.96 mm × 1.56 mm), includes PGOOD and MODE sync, and eliminates compensation - making it optimal for high-current, space-constrained, and system-synchronized POL designs.

Availability

FAN53541UCX is available at Aetrix Electronics and suitable for communication card power, DSP core supply, HDD preamp supply, and set-top box SoC rail applications requiring stable component supply, long-term lifecycle assurance, and consistent parametric performance across production lots.

Supply support for FAN53541UCX 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

ON Semiconductor is a global semiconductor manufacturer specializing in energy-efficient power management, analog, sensor, and connectivity solutions for automotive, industrial, cloud, and consumer markets.

The FAN53541UCX belongs to ON Semiconductor's TinyBuck™ family of high-frequency synchronous buck regulators, designed specifically for compact, high-efficiency point-of-load conversion in portable and space-constrained electronics.

FAQ

What is the recommended input and output capacitor configuration for FAN53541UCX?

The FAN53541UCX requires a 10 µF X5R 0805 ceramic input capacitor (CIN) placed adjacent to VIN and GND balls, plus a 10 nF X7R 0402 bypass capacitor (CIN1) closer to the VIN pin. For output, 20 µF total (e.g., two 10 µF 0805 X5R capacitors) is recommended to ensure stability and transient response. Larger COUT values improve load-step performance without affecting loop stability.

Does FAN53541UCX support external frequency synchronization, and how is it implemented?

Yes, FAN53541UCX supports external frequency synchronization via the MODE pin. When an external square wave (30–70% duty cycle, 525–700 kHz) is applied to MODE, the regulator locks its switching frequency to exactly four times the input signal (4× f_MODE). This enables deterministic EMI reduction and system-level clock domain alignment without requiring additional PLL circuitry.

What is the purpose of the AGND pin on FAN53541UCX, and how should it be routed?

The AGND pin on FAN53541UCX serves as the dedicated analog reference for feedback (FB), enable (EN), mode (MODE), and power-good (PGOOD) circuits. It must be routed separately from power GND planes and tied to the analog section ground pour - avoiding shared traces with high-dV/dt SW or VIN paths. A star-point connection to the main GND plane near the IC minimizes noise coupling into sensitive analog nodes.

How does FAN53541UCX handle startup into a pre-biased output voltage?

FAN53541UCX implements diode emulation mode during startup, which disables reverse current flow through the low-side MOSFET. This prevents the output capacitor from discharging into the IC when VOUT is already biased, eliminating negative voltage transients and ensuring safe, monotonic startup - critical for hot-swap and multi-rail sequencing applications.

What thermal derating guidance applies to FAN53541UCX in a 4-layer PCB with 2 oz copper?

On a standard 4-layer evaluation board (2 oz outer layers, 1 oz inner layers), FAN53541UCX exhibits θ_JA = 38°C/W. To maintain T_J ≤ 125°C, maximum ambient temperature must be limited based on load: e.g., at 4 A and 5 V_IN/1.2 V_OUT, efficiency ≈ 82%, resulting in ~1.05 W IC dissipation - allowing ~97°C ambient before exceeding 125°C junction. Thermal vias under the GND balls and extended copper pours are strongly recommended.