1 Features

1• Operates from a Single Li-Ion Cell (3 V to 5.5 V)

• 6-MHz (typ.) PWM Switching Frequency

• Fixed Output Voltage: 3.3 V

• Up to 1.2-A Maximum Load Capability

• High Efficiency: 94% (typ.) with 3.8-V V IN at

300 mA

• Analog Bypass: 60-mV (typ.) Drop-Out at 600 mA

• Low I Q: 16 μA typical, 25 μA maximum

• Automatic ECO/PWM/Bypass Mode Change

• Forced PWM Mode for Low Output-Voltage Ripple

• Soft-Start Limits Input Current on Start-Up

• Current Overload Protection

• Thermal Overload Protection

• Small Total Solution Size: < 7.5 mm2

2 Applications

• WLAN, WiFi Station Devices

• WiFi RF PC Cards

• Battery-Powered RF Devices

3 Description

The LM3281 is a high-efficiency low-noise miniature

DC-DC converter optimized for powering noise- sensitive wireless connectivity chipsets and RF Front

End Modules (FEMs) from a single Lithium-Ion cell.

The LM3281 is ideal for “always on” applications with

very low unloaded quiescent current of 16 μA (typ.).

The LM3281 steps down an input supply voltage to a

fixed output voltage of 3.3 V with output current up to

1200 mA. Five different modes of operation are used

to optimize efficiency and minimize battery drain. In

Pulse Width Modulation (PWM) mode, the device

operates at a fixed frequency of 6 MHz which

minimizes RF interference when driving medium-to- heavy loads. At light load, the device automatically

enters into Economy (ECO) mode with reduced

quiescent current. In a low-battery voltage condition,

a bypass mode reduces the voltage dropout to 60 mV

(typ.) at 600 mA. If very low output voltage ripple is

desired at light loads, the device can also be forced into PWM mode. Shutdown mode turns the device off

and reduces battery consumption to 0.1 μA (typ.).