Electronic Design

Synchronous Buck Regulator Doubles Output Current In ThinSOT

Combining circuit refinements with process advances, Linear Technology has doubled its synchronous current-mode step-down regulator's output-current capability. Consequently, the LTC3406 offers a 600-mA continuous current output with a 3-V supply. A submicron CMOS process lets this buck regulator fit in a miniature, five-lead ThinSOT package with just a 1-mm profile.

Its operational quiescent current is as low as 20 µA, dropping below 1 µA in shutdown mode. A major contributor to this low figure is the chip's patented burst-mode operation, in which internal power MOSFETs operate intermittently based on load demand. Burst-mode operation also increases efficiency at light loads. The regulator's efficiency varies with load and VIN/VOUT ratios. Both main p-channel and synchronous n-channel MOSFET switches are implemented on-chip.

Designed for applications using one lithium-ion battery, the regulator offers a 2.5- to 5.5-V input voltage range. Its duty cycle is 100%, so its voltage dropout is low. Other features include ±2% output voltage accuracy over the temperature range, as well as low output ripple. Using a 10-µF ceramic capacitor at the output, with an ESR of 6 to 8 mÙ at 1.5 MHz, the output ripple is rated at 5 to 10 mV peak-to-peak.

The device's fixed switching frequency is internally set to 1.5 MHz, allowing the use of miniature surface-mount inductors and capacitors. Only three external components are required for a complete solution. The LTC3406-1.5 and -1.8 offer fixed output voltages of 1.5 V and 1.8 V. The LTC3406's output voltage is adjustable. Since the on-chip reference voltage is 0.6 V, the LTC3406 can go down to a 0.6-V output.

The LTC3406ES5 costs $1.95 in lots of 1000. The -1.8/-1.5 V options cost the same.

Linear Technology, www.linear.com; (408) 432-1900; fax (408) 434-6441.

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