Power Electronics

SOT-23 DC-DC Converters Deliver 95% Efficiency

National Semiconductor has introduced the first two products in a family of miniature, synchronous step-down dc-dc converters for portable systems. The LM3670 and LM3671 feature automatic switchover from PFM to PWM to achieve high efficiency over the entire load, obtaining up to 95% efficiency during continuous switching operation. Typical quiescent current is just 16 µA. The converters also limit noise, generating less than 5-mV peak-to-peak output voltage ripple.

These chips will initially be offered in 5-pin SOT-23 packages. However, in the spring of 2005, the LM3671 will be available in National's micro SMD chip-scale package, which measures just 1.4 mm × 1.1 mm. The LM3671's 2-MHz oscillator frequency also helps to create a small overall dc-dc converter design by enabling use of small external passives. An LM3671 converter design can be completed using a 2.2-µH inductor and two 10-µF capacitors.

Operating from a 2.8 V to 5.5 V input, the LM3671 generates a stepped-down output at a load up to 600 mA. Standard output voltage options include 3.3 V, 1.875 V, 1.8 V, 1.6 V, 1.5 V, 1.375 V, 1.25 V, 1.2 V as well as an adjustable output version.

A low-power version of the LM3671, the LM3670 switches at 1 MHz and delivers up to 300 mA. The LM3670 is available with output voltage options of 1.8 V, 1.875 V, 1.5 V and an adjustable version. The LM3670 requires a small 10-µH inductor and two 4.7-µF capacitors for operation.

Available now, the LM3670 is priced at $1.40 and the LM3671 is priced at $1.60 in 1,000-unit quantities.

For more information, visit www.national.com.

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