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DC/DC converter IC reduces BOM, PCB size

Posted: 20 Dec 2005 ?? ?Print Version ?Bookmark and Share

Keywords:STMicroelectronics? st? DC/DC converter chip? STw4141?

STw4141 DC/DC converter chip

STMicroelectronics (ST) introduced a DC/DC converter chip that allows two different output voltages to be generated using a single external coil. According to the company, the new 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 1.2V, but can be as low as 0.9V in new designs, and the I/O circuitry, which typically runs from a 1.5V or 1.8V supply rail. These supplies must typically be derived from a Li-ion (or NiMH/NiCd) battery whose output voltage varies from 2.7V to 5.5V according to its discharge level, making low drop-out (LDO) converters too inefficient in these applications. Therefore, current practice is to use two standard step-down DC/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.

By allowing two different output voltages to be obtained using a single external coil, said ST, the STw4141 allows the BOM to be cut by up to 40 percent and PCB size to be reduced by 30 percent compared to previous standard supply solutions. In addition, the STw4141 does not 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 0.9V to 1.8V with 50mV steps are also available. The devices provide a maximum load capability of 200mA on VOUT1 (peripheral supply) and 400mA on VOUT2 (core supply).

During full power operation, the device operates in externally synchronized or fixed frequency pulse width modulation (PWM) mode to deliver full output current capability while minimizing interference to sensitive RF and data acquisition circuits. During standby operation, the device can switch automatically to pulse frequency modulation (PFM) mode, reducing quiescent current to 90?A (typical) to maximize battery life. The selection of PWM/PFM modes can be automatic or controlled by the application via the AUTO and MODE/SYNC inputs. A shutdown mode is also provided, further reducing battery consumption to less than 1?A (typical).

The STw4141 includes many additional features, including soft-start, current limit protection and thermal shutdown protection. It is housed in a compact TFBGA package. The only external components required are a 4.7?H coil, a 10?F input capacitor and two 22?F output capacitors, allowing a minimal volume of 7-by-8mm board area and 1.2mm height for a complete dual-supply solution.

Engineering samples of the STw4141 have already been shipped to key customers. Full sample availability, together with volume production, is expected in Q1 2006. For quantities of 1,000 to 5,000 units, the new DC/DC converter chip is priced at $1.4.

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