Dc-dc converter provides two rails from one external coil - Embedded.com

Dc-dc converter provides two rails from one external coil


STMicroelectronics has introduced a dc-to-dc converter that allows two different output voltages to be generated using just one external coil. The STw4141 is specifically designed to supply digital baseband and multimedia processors in portable applications such as mobile phones, digital still cameras, and PDAs, where designers operate under tight constraints in terms of pcb area, cost, and power consumption.

The processors used in these applications usually require separate supplies for the core, which is typically powered by 1.5, 1.3 or 1.2 V, but can be as low as 0.9 V, and the I/O circuitry, which typically runs from a 1.5- or 1.8-V supply rail. These supplies must typically be derived from a battery whose output voltage varies from 2.7 to 5.5 V, making low drop-out (LDO) converters too inefficient in these applications. Therefore, current practice is to use two standard step-down dc-to-dc converters, each of which requires an external coil, two or more external capacitors and, in some cases, external resistors to set the output voltage.

In addition to the space savings, the STw4141 doesn't require resistive dividers to set the output voltages. The standard family provides all the most commonly requested combinations of preset core and I/O supplies, while custom voltage options in the range of 0.9 to 1.8 V with 50-mV steps are available. The devices provide a maximum load capability of 200 mA on VOUT1 (peripheral supply) and 400 mA on VOUT2 (core supply).

Other features include soft-start, current limit protection, and thermal shutdown protection. It's housed in a TFBGA package. Pricing is in the range of $1.4 in quantities of 1000 to 5000 units. Further information can be found at www.st.com/stonline/products/literature/bd/11655/stw4141.htm.

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