Despite the proud claim that "everything's bigger" in the Lone Star State, at Texas Instruments we realize that sometimes it pays to be small. The smaller the better in fact when it comes to electronics for mobile devices. As mobile device screen sizes and resolution steadily increased over the last five years, so has the need for more efficient power conversion, despite the fact that the space available for the display electronics has steadily decreased.
The need for compact, high-performance, display solutions eventually led display vendors to introduce COG (Chip-on-Glass) technology, which typically requires bipolar power supply rails in the ±5 V range. TI's first power supply solutions for these displays used a boost converter and an inverting buck-boost converter. Our next generation used a novel SIMO (single inductor, multiple output) topology, which reduced the solution size considerably by only requiring one inductor. The current state-of-the-art solution from TI, the TPS65132, uses an inductive boost and an inverting charge pump to achieve overall power efficiencies greater than 86%, despite the extremely small solution size (see figure below).
The TPS65132 is available factory-programmed with default voltage settings of ±5.0 V, ±5.4 V or ±5.5 V, but it can be re-programmed by the customer in 100 mV steps and 1% accuracy to any voltage in the range ±4 V to ±6 V via the integrated I2C interface. Separate enable pins for the positive and negative outputs provide additional power sequencing flexibility. Another advantage of the topology used in the TPS65132 is that there is no need to balance the loads on the positive and negative outputs – one can be 100% loaded while the other is 0% loaded without any loss of performance.
The table below compares three of TI's most popular bipolar supply solutions. Originally developed for LCD bias applications, they are equally suitable for use in a wide range of applications supplied from a battery or 3.3 V supply. (For even higher output voltages, see the TPS65130/1 devices.)