The industry's first family of low dropout (LDO) voltage regulators/supervisors to support the dual-supply voltage needs of low-power digital signal processors (DSPs) was announced by Texas Instruments (TI). The devices regulate 3.3 volts and a second fixed (1.8V or 2.5V) or programmable voltage in a single 28-pin integrated circuit (IC) package, thus eliminating three ICs from single-core DSP designs and even more from complex applications using multiple DSPs. Moreover, they provide the relative simplicity and low-cost found in linear regulator power supply designs.

"These devices are part of TIıs growing family of power management products that support the increasing demands placed on power supplies by todayıs DSPs," said Bob Newton, analog product specialist for TI's Advanced Analog Products. "Combined with the worldıs lowest power DSPs from TI, the new LDO family with its advanced packaging provides DSP solutions for a broad array of high-performance, low-power signal processing applications. The low dropout voltage and micropower operation of the dual PMOS regulators make them especially suitable in power-sensitive, battery driven applications. Single-DSP systems, such as wireless handsets, Internet Protocol phones and digital hearing aids, benefit from reduced chip count and space. Multi-DSP systems, such as telecom infrastructure equipment, can take advantage of the dual regulator's capability to power up to four DSPs from a single package."

The new devices, designated the TPS73HD301, HD318 and HD325, provide greater benefit for systems using multiple DSPs because of TIıs PowerPad, the patented thermally-enhanced Thin Shrink Small Outline Package. The package enables excellent power dissipation in a small surface mount package. Either output can provide up to 750 milliamps of current, enough to power four low-power DSPs from one package. This ability to supply multiple DSPs reduces system power consumption and board size in telecommunications infrastructure equipment using multiple DSPs. Cellular base stations, telephone company (telco) switches, internet service provider (ISP) routers, remote servers and packet gateways can all benefit from these devices and the low power DSPs they support.

Low Dropout Voltage and Output Tolerance are Major Advantages

Each product in the family is built using a PMOS pass element, resulting in a dual regulator with micropower supply current requirements and very low dropout. Typical dropout for the 3.3V output is only 350 milivolts at 750 miliamps of output current. Low supply current and low dropout voltage are key requirements for extending battery life in portable equipment applications. The device output also has a tolerance of +/- 2%.

More Power Saving Features

These regulators support a low power logic-enabled standby mode to minimize power drain in "off" states to further reduce battery consumption. The supply current used by the device totals only 600 to 800 microamps for the dual regulator over the full range of operation. When combined with a low-power DSP from TI's TMS320C54x family (designated products listed below), battery-powered systems using these LDO regulators have a longer useful life.

Click here for table.

Although intended primarily to provide support for their own DSPs, these parts are nonetheless significant. They represent a continuing pattern by TI to provide the external analog requirements for DSP solutions so that the company can be a single source shop for such applications -- and a very successful strategy it has become. The BMW-sounding part numbers of TPS73HD318 and 315 provide the 3.3-V output plus 3.18 V and 3.25 V respectively. The 301 part provides the 3.3-V output plus one that is adjustable from 1.2 to 9.75 V, of which the 1.2 V is a lower output than has been available before (for an upcoming product?); the 9.75 V may be a touch low for some of the 10-V applications that are still out there.

The dropout is low but not quite as low as some of TI's previous products, but the great virtues here are the provision of the two outputs and sufficient power to drive multiple microprocessors. TI say here up to four but I think that could be five in some circumstances. Even so, there is a price premium for going this route if you don't use the output current to its fullest. The crossover would be in the region between powering two and three DSPs, as discrete LDOs are available for less than $0.50. There would be size issues as well with multiple packages and the usually not-considered handling and loading costs for multiple parts. The press release could be taken to be misleading when it mentions the output accuracy to be +/- 2%. That is valid for all the outputs except the 1.8-V output where the accuracy is +/- 3%. The active-low resets with 200 ms delay, except on the 1.8-V output as well. The choice of the 28-pin TSSOP was presumably made because of the heat dissipation needs because there are, in fact, 12 unused leads and there are another 10 leads which wouldn't necessarily have had to be brought out of the IC at all for the majority of circuit designs.