Power Electronics

Step-Down Converters

Maxim Integrated Products introduces the MAX1556/MAX1557 step-down, dc-dc converters for use in digital still cameras, mobile phones, PDAs, palmtop computers and other handheld portable equipment. Available in a tiny 3mm × 3-mm, 10-pin QFN package, the MAX1556 delivers up to 1.2 A and the MAX1557 delivers up to 600 mA of load current.

The devices offer a low quiescent current of 16 µA and 27 µA in dropout. A proprietary topology provides the benefits of high fixed-frequency operation, while still providing better than 95% efficiency at both light and full loads.

The MAX1556/MAX1557 have a unique, wideband control loop and voltage-positioning feature. By minimizing the amplitude and duration of overshoot and undershoot in response to load transients, this unique capability allows less than 50-mV peak-to-peak load transient response and 4 µs load step recovery time. Other dc-dc converters with high gain-control loops use external compensation to maintain tight dc load regulation, but still allow large voltage droops of 5% or greater for several hundreds µs during transients. If, for example, the load is a CPU running at 600 MHz, then a dip lasting 100 µs corresponds to 60,000 CPU clock cycles.

The MAX1556/MAX1557 offer an internal low-on-resistance MOSFET switch and synchronous rectifier to maximize efficiency and dropout performance while minimizing external component count. Both devices also feature an adjustable soft-start to minimize battery transient loading. The input voltage range is 2.6 V to 5.5 V, allowing the use of 1-cell Li-Ion (Li+) or 3-cell alkaline/NiMH batteries. With two input-select pins, designers can select an adjustable output on either device, or preset 3.3 V, 2.5 V or 1.8 V for the MAX1556 and 1.5 V, 1.3 V or 1.0 V for the MAX1557, without external feedback resistors.

The devices are specified for the extended temperature range (-40°C to 85°C). Pre-assembled evaluation kits with recommended external components are available to speed designs. Prices start at $1.55 for the MAX1556 and $1.45 for the MAX1557.

For more information, visit www.maxim-ic.com.

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