March 2008
FAN5355
1A / 0.8A, 3MHz Digitally Programmable TinyBuckTM Regulator
Features
Description
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.
91% Efficiency at 3MHz
800mA or 1A Output Current(1)
2.7V to 5.5V Input Voltage Range
6 or 7-bit VOUT 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
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.
High-Efficiency, Low-Ripple, Light-Load PFM
Smooth Transition between PWM and PFM
37μA Operating PFM Quiescent Current
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. 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).
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
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.
Applications
SmartReflex™-Compliant Power Supply
Split Supply DSPs and μP Solutions OMAP™, XSCALE™
Cell Phones, Smart Phones, PDAs, Digital Cameras, and
Portable Media Players
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.
Micro DC-DC Converter Modules
Handset Graphic Processors (NVIDIA®, ATI)
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.
I2C is a trademark of Philips Corporation.
SmartReflex and OMAP are trademarks of Texas Instruments.
XSCALE is a trademark of Intel Corporation.
The FAN5355 is available in 10-lead MLP (3x3mm) and
12-bump CSP packages.
NVIDIA is a registered trademark of NVIDIA Corporation.
© 2008 Fairchild Semiconductor Corporation
FAN5355 • Rev. 1.0.4
www.fairchildsemi.com
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