The FAN5355 device is a high-frequency, ultra-fast transient response, synchronous step-down DC-DC converter optimized for low-power applications using small, low-cost inductors and capacitors. The FAN5355 supports up to 800mA or 1A⁽¹⁾ load current.

The device is ideal for mobile phones and similar portable applications powered by a single-cell Lithium-Ion battery. With an output voltage range adjustable via I²C™ interface from 0.75V to 1.975V, the device supports low-voltage DSPs and processors, core power supplies in smart phones, PDAs, and handheld computers.

The FAN5355 operates at 3MHz (nominal) fixed switching frequency using either its internal oscillator or external SYNC frequency.

During light-load conditions, the regulator includes a PFM mode to enhance light-load efficiency. The regulator transitions smoothly between PWM and PFM modes with no glitches on V_OUT. Normal PFM (NPFM) mode offers the lowest quiescent current, at the expense of setpoint accuracy. Enhanced PFM (EPFM) mode features higher accuracy, as well as a 25kHz minimum PFM frequency, designed to prevent the regulator from operating in the audible range. In shutdown, the current consumption is reduced to less than 2µA, using software shutdown (EN = 1 with EN_DCDC = 0), and less than 200nA in hardware shutdown (EN = 0).

The serial interface is compatible with Fast/Standard and High-Speed mode I²C™ specifications, allowing transfers up to 3.4Mbps. This interface is used for dynamic voltage scaling with 12.5mV voltage steps, for reprogramming the mode of operation (PFM or Forced PWM), or to disable/enable the output voltage.

The chip's advanced protection features include short-circuit protection and current and temperature limits. During a sustained over-current event, the IC shuts down and restarts after a delay to reduce average power dissipation into a fault.

During start-up, the IC controls the output slew rate to minimize input current and output overshoot at the end of soft-start. The IC maintains a consistent soft-start ramp, regardless of output load during start-up.

The FAN5355 is available in 10-lead MLP (3x3mm) and 12-bump CSP packages.

• 91% Efficiency at 3MHz
• 800mA or 1A Output Current
• 2.7V to 5.5V Input Voltage Range
• 6 or 7-bit V_OUT Programmable from 0.75 to 1.975V
• 3MHz Fixed-Frequency Operation
• Excellent Load and Line Transient Response
• Small Size, 1µH Inductor Solution
• ±2% PWM DC Voltage Accuracy
• 35ns Minimum On-Time
• High-Efficiency, Low-Ripple, Light-Load PFM
• Smooth Transition between PWM and PFM
• 37µA Operating PFM Quiescent Current
• Software Selectable 25kHz Minimum PFM Frequency Prevents Audible Noise in PFM Mode
• I²C™-Compatible Interface up to 3.4Mbps
• Pin-Selectable or I²C™ Programmable Output Voltage
• On-the-Fly External Clock Synchronization
• 10-lead MLP (3 x 3mm) or 12-bump CSP Packages

• SmartReflex™-Compliant Power Supply
• Split Supply DSPs and µP Solutions OMAP™, XSCALE™
• Cell Phones, Smart Phones, PDAs, Digital Cameras, and Portable Media Players
• Micro DC-DC Converter Modules
• Handset Graphic Processors (NVIDIA^®, ATI)