onsemi FAN53528BUC08X

Overview

FAN53528BUC08X from onsemi is a digitally programmable 2.4 MHz synchronous buck regulator delivering up to 3.0 A continuous output current, with I²C interface (up to 3.4 Mbps), 0.35 V–1.14375 V programmable output in 6.25 mV steps, and fixed 0.4 V / 0.6 V power-up defaults - used for core voltage regulation in ARM/Tegra/OMAP application processors.

For engineers reviewing the FAN53528BUC08X datasheet, pinout, applications, or equivalent options, key selection criteria include its 2.4 MHz fixed-frequency operation, PFM/PWM auto-mode transition, 50 µA quiescent current in light-load PFM mode, WLCSP-15 package footprint, and I²C-programmable slew rate control for dynamic voltage scaling.

Technical Context

The FAN53528BUC08X implements a proprietary non-linear fixed-frequency PWM modulator with synchronous rectification, enabling fast load transient response (<±20 mV at 10 mA ↔ 700 mA) while maintaining stable 2.4 MHz switching across 2.5–5.5 V input and 0–3.0 A load. Its architecture eliminates ESR dependency, supporting ceramic output capacitors.

It integrates dual VSEL register banks (VSEL0/VSEL1), hardware EN control with internal 250 kΩ pull-down, and I²C slave address 0xA0. Power-up defaults are VOUT = 0.4 V (VSEL0) and 0.6 V (VSEL1), with no EN delay - distinguishing it from EUC48X variants that include 5 ms EN delay.

Key Specifications

Pinout & Package

Package: 15-bump Wafer-Level Chip Scale Package (WLCSP), 1.310 mm × 2.015 mm, 0.4 mm ball pitch, Case 567QS.

Key Features

Applications

Equivalent & Alternatives

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

Compared with TPS628641RQYR and RTQ2132BGQW, the FAN53528BUC08X uniquely combines dual-VSEL hardware selection, 50 µA PFM quiescent current, and 2.4 MHz fixed-frequency operation - making it optimal for space-constrained, battery-sensitive mobile SoC core supplies requiring rapid, deterministic voltage transitions.

Availability

FAN53528BUC08X is available at Aetrix Electronics and suitable for smartphone baseband processors, LPDDR4 memory power delivery, and ultra-mobile PC SoC auxiliary rails requiring stable component supply, long-term lifecycle support, and traceable wafer-lot sourcing.

Supply support for FAN53528BUC08X 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

onsemi (Nasdaq: ON) is a global semiconductor leader delivering energy-efficient, intelligent power and sensing solutions for automotive, industrial, cloud, medical, and IoT applications.

The FAN53528 series was designed specifically for high-efficiency, digitally programmable core voltage regulation in mobile application processors - emphasizing small WLCSP footprint, I²C-based DVFS control, and robust thermal/current protection.

FAQ

What is the default power-up output voltage of the FAN53528BUC08X?

The FAN53528BUC08X powers up with two default output voltages: 0.4 V when the VSEL pin is logic LOW (selecting VSEL0 register), and 0.6 V when VSEL is HIGH (selecting VSEL1 register). These values are factory-programmed and stored in non-volatile register defaults, ensuring predictable boot behavior without I²C initialization. The FAN53528BUC08X does not include an EN delay, so VOUT begins soft-start immediately upon EN assertion.

Does the FAN53528BUC08X support both PFM and PWM modes, and how is mode selection controlled?

Yes, the FAN53528BUC08X supports automatic PFM/PWM mode transition based on load current, and forced PWM mode. Mode selection is determined jointly by the VSEL pin state and MODE bits (bits 1:0) in Control Register 02h. When VSEL is LOW and MODE = '10', Auto PFM/PWM is active; when VSEL is HIGH and MODE = '11', Forced PWM is enabled. This dual-control scheme allows hardware- or software-driven mode selection, giving system designers flexibility in balancing efficiency and noise requirements. The FAN53528BUC08X achieves 50 µA quiescent current in PFM mode.

What is the I²C slave address of the FAN53528BUC08X, and does it support High-Speed Mode?

The FAN53528BUC08X uses I²C slave address 0xA0 (7-bit address 0x50, R/W bit appended), distinct from DUC/EUC/GUC variants which use 0xA4. It fully supports Standard (100 kHz), Fast (400 kHz), Fast Plus (1 MHz), and High-Speed Mode (3.4 Mbps) - the latter enabled via HS master code transmission followed by REPEATED START. This allows rapid voltage reprogramming during CPU DVFS events. All register reads/writes for the FAN53528BUC08X follow standard I²C packet structure with MSB-first data transfer.

How does the FAN53528BUC08X handle output voltage transitions, and what slew rate options are available?

The FAN53528BUC08X provides programmable positive-edge slew rate control via the SLEW bits (6:4) in Control Register 02h, offering eight discrete settings from 0.5 mV/s to 64 mV/s. This prevents overshoot during upward voltage transitions (e.g., CPU frequency ramp-up) and ensures controlled settling. Downward transitions rely on load discharge; the IC halts switching until VOUT reaches the new setpoint. The FAN53528BUC08X's slew control is implemented entirely in hardware, requiring no host timing loops or external components.

What thermal and overcurrent protections are built into the FAN53528BUC08X?

The FAN53528BUC08X integrates thermal shutdown at 150°C (with 17°C hysteresis) and peak current limiting at 4.75 A typical. If 16 consecutive current-limit cycles occur, the device enters tri-state and waits ~1700 s before attempting restart - preventing thermal runaway during sustained short-circuit or overload. Under-voltage lockout (UVLO) activates at 2.45 V with 350 mV hysteresis, and input overvoltage protection (OVP) triggers at 6.15 V. All protections are internal and require no external components - a key reliability feature of the FAN53528BUC08X.