onsemi FAN5904BUC01X

Overview

FAN5904BUC01X from ON Semiconductor is a multi-mode synchronous buck converter optimized for dynamic supply bias of RF power amplifiers in GSM/EDGE, 3G/3.5G, and 4G mobile handsets. It delivers up to 2.3 A in High-Power PWM Mode (3 MHz), supports 0.40–3.50 V dynamically adjustable output via analog VCON control, integrates a 35 mΩ bypass FET, and uses a single 470 nH inductor in a 1.71 mm × 1.71 mm WLCSP package.

For engineers reviewing the FAN5904BUC01X datasheet, pinout, applications, or equivalent options, this device is selected for fast transient response (<10 µs step settling), high-efficiency PFM operation across full VOUT range, and seamless transition between PWM, Auto, and Bypass modes in polar PA biasing systems.

Technical Context

The FAN5904BUC01X implements current-mode control with dual switching architectures: 3 MHz fixed-frequency PWM in High-Power Mode (MODE = 0) and 6 MHz PWM + PFM in Low-Power Auto Mode (MODE = 1). Its analog VCON input (0.16–1.40 V) linearly scales VOUT with 2.5× gain, enabling precise PA envelope tracking. The integrated 35 mΩ bypass FET activates automatically when VIN − VPMOS − VOUT exceeds 295–385 mV (HP mode) or 140–240 mV (LP mode), supporting up to 3.0 A load current with minimal dropout.

It features separate current limits per mode (2.7–3.9 A for HP, 1.35–1.95 A for LP), programmable MODE/SYNC/BPEN logic inputs, and dedicated AGND/PGND separation for RF noise suppression. Startup time is 50–60 µs, and output regulation maintains ±25 mV load regulation over 20 mA–2 A.

Key Specifications

Pinout & Package

1.71 mm × 1.71 mm, 16-bump, 0.4 mm pitch Wafer-Level Chip-Scale Package (WLCSP) with bumps face down in top-through view.

Key Features

Applications

Equivalent & Alternatives

The following parts are listed as comparable options for similar multi-mode buck converter applications.

Compared with MPQ4420AGU-A and TPS62130ARGTR, the FAN5904BUC01X uniquely combines analog VCON-based dynamic VOUT scaling, sub-10 µs transient response, integrated bypass FET, and dual-mode (3/6 MHz) operation-making it irreplaceable for GSM polar and 4G envelope-tracking PA bias where timing, efficiency, and analog simplicity are co-critical.

Availability

FAN5904BUC01X is available at Aetrix Electronics and suitable for GSM/EDGE handset design, 3G/4G mobile data card development, and LTE-A hotspot RF front-end production requiring stable component supply and long-term lifecycle support.

Supply support for FAN5904BUC01X 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 supplier delivering energy-efficient, high-performance silicon solutions for automotive, industrial, cloud computing, and mobile applications.

The FAN5904BUC01X belongs to ON Semiconductor's RF Power Management product line, engineered specifically for dynamic supply bias of cellular power amplifiers in space- and efficiency-constrained mobile platforms.

FAQ

What is the key functional difference between FAN5904BUC01X and FAN5904BUC00X?

The FAN5904BUC01X enables Pulse Frequency Modulation (PFM) operation across the full output voltage range (0.40–3.50 V), while the FAN5904BUC00X restricts PFM to VOUT < 1 V only. This makes the FAN5904BUC01X superior for 3G/4G applications requiring high efficiency at moderate output voltages (e.g., 1.8–2.8 V) under light loads, whereas FAN5904BUC00X targets ultra-low-noise GSM bias where PFM is limited to lowest VOUT segments.

How does the FAN5904BUC01X achieve <10 µs output voltage step response?

The FAN5904BUC01X achieves <10 µs VOUT rise/fall time through high-bandwidth current-mode control, optimized error amplifier slew rate, and minimized propagation delay in its analog VCON-to-VOUT path. It is validated under ∆VOUT ≤ 3.0 V steps with RLOAD ≤ 7 Ω and COUT = 2 × 4.7 µF, meeting GSM inter-slot timing for both High-Power and Low-Power modes - a performance metric confirmed in Figures 38–41 of the official datasheet.

Can the FAN5904BUC01X operate without an external inductor?

No, the FAN5904BUC01X requires an external 470 nH inductor connected between SW and VOUT. It is a synchronous buck controller with integrated MOSFETs but no internal energy storage; omitting the inductor prevents regulation and risks immediate device failure due to uncontrolled current flow. The 470 nH value is specified for minimal PCB footprint and optimal efficiency in mobile RF layouts.

What is the role of the BPEN pin on the FAN5904BUC01X?

The BPEN pin on the FAN5904BUC01X forces activation of the integrated 35 mΩ bypass FET when driven HIGH, overriding automatic threshold-based entry. When pulled LOW, bypass activation follows internal voltage comparisons (e.g., VIN − VPMOS − VOUT > 295 mV in HP mode). This enables deterministic, timing-controlled bypass for VSWR protection or burst-mode PA operation independent of analog conditions.

Does the FAN5904BUC01X support I²C or other digital interfaces?

No, the FAN5904BUC01X does not include I²C, SPI, or any digital communication interface. It is an analog-controlled DC-DC converter relying exclusively on the VCON voltage input (0.16–1.40 V) for output regulation, plus digital logic inputs (MODE, BPEN, SYNC, EN) for mode selection and control. All configuration and dynamic adjustment occur via analog voltage levels and discrete logic states - no firmware or serial protocol is involved.