STMicroelectronics’ Converter Provides Two Regulated Voltages Using One Coil

STMicroelectronics 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 printed circuit board (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.

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).

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.