Line Card

FAN5355 1A/0.8A 3MHz Digitally Programmable DC/DC Converter


【Basic Info】

【Product Feature】

* 93% Efficiency at 3MHz
* 800mA or 1A Output Current
* I2C™-Compatible Interface up to 3.4Mbps
* 6-bit VOUT Programmable from 0.75V to 1.975V
* 2.7V to 5.5V Input Voltage Range
* 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
* Pin-Selectable or I2C™ Programmable Output Voltage
* On-the-Fly External Clock Synchronization
* 10-lead MLP (3 x 3mm) or 12-bump CSP Packages


* Cell Phones, Smart Phones
* 3G, WiFi®, WiMAX™, and WiBro® Data Cards
* Netbooks®, Ultra-Mobile PCs
* SmartReflex™-Compliant Power Supply
* Split Supply DSPs and µP Solutions OMAP™, XSCALE™
* Mobile Graphic Processors (NVIDIA®, ATI)
* LPDDR2 and Memory Modules


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 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, and memory modules 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 VOUT. In hardware shutdown, the current consumption is reduced to less than 200nA.

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 startup, 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 startup.

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