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Novel DC/DC Converter from STMicroelectronics Provides Two Regulated Supply Rails Using Only One External Coil


Geneva, December 14, 2005 - STMicroelectronics (NYSE: STM), one of the world’s largest semiconductor manufacturers and the world’s leading supplier of semiconductor products for power conversion according to independent market analyst iSuppli, has introduced an innovative and patented DC/DC converter chip that allows, for the first time, two different output voltages to be generated using a single 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. In these demanding applications, the STw4141 allows significant reductions to be achieved in both the PCB area and the manufacturing cost of the power supply subsystem.

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 1.5 or 1.8V supply rail. These supplies must typically be derived from a lithium-ion (or NiMH/NiCd) battery whose output voltage varies from 2.7 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. The external coils significantly impact the bill of material (BOM), the PCB area and the application cost.

By allowing two different output voltages to be obtained using a single external coil, the STw4141 allows the BOM to be cut by up to 40% and PCB size to be reduced by 30% compared to previous standard supply solutions. For example, a complete STw4141 power supply subsystem solution can be implemented using only 56mm2 of PCB area, compared with around 80mm2 for the best previous alternative approaches. Moreover, 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 - 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).

Based on voltage-mode buck architecture, the STw4141 delivers its significant BOM and PCB area benefits without sacrificing performance: efficiency of up to 92% is best-in-class and both output voltages are guaranteed to be within 100mV of the specified values. Moreover, high efficiency is maintained over a very wide range of I/O output currents, from below 10mA up to the full 200mA limit. During full power operation, the device operates in externally synchronized or fixed frequency PWM (Pulse Width Modulation) 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 PFM (Pulse Frequency Modulation) mode, reducing quiescent current to 90 microamps (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 microamp (typical).

The STw4141 includes many additional features, including soft-start, current limit protection and thermal shutdown protection. It is housed in a compact TFBGA 3x3x1.2 package, which offers the smallest possible size for space-critical applications such as cell phones. The only external components required are a small 4.7-microHenry coil, a 10-microFarad input capacitor and two 22-microFarad output capacitors, allowing a minimal volume of 7x8mm 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. US pricing is in the range of $1.4 in quantities of 1000 to 5000 units.

About STMicroelectronics
STMicroelectronics is a global leader in developing and delivering semiconductor solutions across the spectrum of microelectronics applications. An unrivalled combination of silicon and system expertise, manufacturing strength, Intellectual Property (IP) portfolio and strategic partners positions the Company at the forefront of System-on-Chip (SoC) technology and its products play a key role in enabling today’s convergence markets.
The Company’s shares are traded on the New York Stock Exchange, on Euronext Paris and on the Milan Stock Exchange. In 2004, the Company’s net revenues were $8.76 billion and net earnings were $601 million. Further information on ST can be found at


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