The LTC3105, a new high-performance synchronous boost CONVERTER, which incorporates maximum power point control (MPPC) and starts up with inputs as low as 250mV, has been released by Linear Technology.

The device operates over an extremely wide input range of 0.2V to 5V, making it ideal for harvesting energy from high-impedance alternative power sources, including photovoltaic cells, thermoelectric generators (TEGs) and fuel cells. The LTC3105’s internal 400mA synchronous SWITCHes maximize EFFICIENCY while its Burst Mode operation offers quiescent current of only 22uA, further optimizing converter efficiency over all operating conditions. A user-programmable MPPC set point maximizes the energy that can be extracted from any power source without collapsing its internal voltage.

The LTC3105 is ideally suited to power wireless sensors and data acquisition applications. Surplus or ambient energy can be harvested and then used to generate system power in lieu of traditional wired or battery power, which may be expensive or impractical. Typically, these applications require very low average power, but require periodic pulses of higher load current. For example, the LTC3105 can be used in wireless sensor applications where the power load is extremely low when the sensor is in standby mode, interrupted by periodic high load bursts, when the circuitry is powered up to take measurements and transmit data.

The device offers an auxiliary LDO that delivers up to 6mA of output current to power external microcontrollers and sensors while the main output is charging. Once fully charged, the main output can deliver voltages as high as 5.25V with up to 100mA of output current. It can also regulate VOUT even when VIN is greater than or equal to VOUT, offering further design flexibility. In shutdown, the LTC3105 offers output disconnect, isolating VIN from VOUT, requiring only 4uA of quiescent current. The combination of the LT3105’s 3mm x 3mm DFN package (or MSOP-12) and very small external components offers a very compact solution for energy harvesting applications.

The LTC3105EDD is available in a 10-lead 3mm x 3mm DFN package and the LTC3105EMS is available in an MSOP-12 package, says the company.

This article was taken from: electropages.com

During 2003, the focus in dc-dc converters shifted from the actual converters to the distributed-power architectures using these devices. Sure, many announcements heralded better dc-dc converter performance. But even greater attention was paid to architectural developments that promise to bolster performance as well as reduce cost and space requirements for power systems.

Several vendors expressed their support for the intermediate voltage bus architecture (IBA) by introducing the necessary bus converters. Even the IC manufacturers got in the game by offering bus converter chips and chip sets. Simultaneously, a mounting number of nonisolated point-of-load converters (POLs) debuted. Many of these devices are no doubt aimed at IBA applications, which rely more on nonisolated point-of-load converters than on bricks.

Meanwhile, Vicor unveiled the Factorized Power Architecture (FPA) and a related set of BGA-style power components. The performance specifications FPA promised were outstanding. But its approach of distributing a pre-regulated but nonisolated high-voltage dc bus to a series of isolated POLs generated wonder and confusion.

By now, some of that confusion may have dissipated since the company openly discussed the new approach’s rationale and principles of operation. Vicor also removed a potential hurdle to commercializing FPA by licensing it to Celestica. As the electronics industry continues to recover, the battle between FPA and IBA should heat up.

A general interest in nonisolated POLs has led to a proliferation of these devices. Many hundreds of models have emerged to provide countless combinations of voltages, currents, and package types. The glut of part numbers has many clamoring for standardization.

In response, some vendors have adopted the footprint and pinout of Tyco’s Austin series. Others have opted for alternatives like Texas Instruments’ POL alliance. Meanwhile, Datel has advocated the eighth brick as a POL standard.

Power-supply vendors will also try to resolve how much of the dc-dc converter should be digital. Microcontrollers are now being used to add features and enhance performance for otherwise analog designs. But some vendors want to push digital further, using it to manage the control loop and create a more flexible converter design.

This article was taken from: Electronic Design

For use in space power systems, more than 50 dc/dc converter modules grouped into four families deliver up to 120W of output power and operate reliably in harsh radiation environments. Reportedly, they are the first dc/dc converters with a guaranteed radiation tolerance through long-term exposure to low dose radiation. Features of the SVSA, SVHF, SVTR, and SVFL product families include 6W to 120W of output power, single and dual outputs, characterization and guarantee to 30 krads (Si) per the company’s RHA plan specified per MIL-PRF-38534, Appendix G, Level P with 2x margin, and characterization, and testing for TID at HDR and LDR to the MIL-PRF-38534 Class H element evaluated components standard. The space series units are available now with pricing beginning at $950 each for the 6W SVSA Series in OEM quantities. VPT INC., Blacksburg, VA. (425) 353-3010.

This article was taken from: Electronic Design

How a 1ppm d/a converter can ease precision instrumentation design problems. By Maurice Egan. Original article here on NewElectronics.co.uk.

The push to improve the precision of instrumentation systems has led to performance improvements in d/a converters beyond 16bits, a benchmark previously achieved with cumbersome, expensive and slow Kelvin-Varley dividers.

Over time, however, the definition of what constitutes a precision d/a converter has changed as markets and technologies have evolved. Advances in semiconductor processing, d/a converter design and calibration techniques are enabling highly linear d/a converters which are stable and fast settling, while delivering a 20bit performance which is better than 1ppm. These small ics have guaranteed specifications, do not require calibration and are easy to use.

Applications for a 1ppm d/a converter vary from gradient coil control in medical MRI systems to precision source and positioning in mass spectrometry and test and measurement applications.

Performance measures
The circuit in Fig 1 delivers 1ppm performance; its key specifications are integral nonlinearity, differential nonlinearity and a peak to peak noise of 0.1Hz to 10Hz.

In Fig 1, U1 is a 20bit d/a converter with 1ppm linearity specifications. U2, a precision dual amplifier, is a force-sense buffer for the d/a converter reference inputs. U3, a precision output buffer, is required for load driving; its key requirements are similar to that of the reference buffers, including: low noise; low offset voltage; low drift; and low input bias current.

Even though precision sub ppm components are available, building a 1ppm system is not a task that should be taken lightly. The major contributors to errors in 1ppm accurate circuits are noise, temperature drift and thermoelectric voltages.

* Noise
To enable a true 1ppm system, noise contributions needs to be minimised. The noise spectral density of U1 is 7.5 nV/vHz. U2 and U3 specify noise density of 2.8 nV/vHz, much lower than the d/a converter’s contribution.
Wideband noise can be filtered, but low frequency noise in the 0.1Hz to 10Hz range (1/f) cannot and the most effective method of minimising this is in component optimisation and selection. U1 generates 0.6µV p-p of noise in the 0.1Hz to 10Hz bandwidth, much less than the 1LSB level (19µV for a ±10V output). The design target for 1/f noise in the system should be approximately 0.1 LSB or around 2µV. The three amplifiers in the signal chain generate a total of approximately 0.2µV p-p of noise at the circuit output. Add this to the 0.6µV p-p of U1 and the total expected 1/f noise is 0.8µVp-p.

* Temperature drift
Temperature drift is another major source of error in precision circuits. U1 exhibits a temperature coefficient of 0.05ppm/^°C. U2 drifts at 0.6µV/^°C, which introduces an overall 0.03 ppm/^°C drift into the circuit. U3, meanwhile, contributes a further 0.03 ppm/^°C of output drift. These contributions add up to 0.11 ppm/^°C. For scaling and gain circuits, low drift, thermally matched resistor networks are recommended, such as Vishay series 300144Z and 300145Z.

* Thermoelectric voltages
Thermoelectric voltages are the result of the Seebeck effect, where temperature dependent voltages are generated at dissimilar metal junctions. The generated voltage can be anywhere between 0.2µV/°C for a copper to copper junction and 1mV/°C for a copper to copper oxide junction.
Thermoelectric voltages manifest as a low frequency drift similar to 1/f noise and can be greatly reduced by keeping all connections clean and oxide free as well as shielding circuitry from air currents. Fig 4 shows the difference in voltage drift between a circuit that is open to air currents and a circuit that is shielded.

Long term stability
Precision analogue ics are stable devices, but do undergo long term age related changes. The d/a converter’s long term stability is typically better than 0.1ppm/1000hr at 125°C, but the aging is not cumulative; rather, it follows a square root rule. If a device ages at 1ppm/1000hr, it will age at v2ppm/2000hr, v3ppm/3000hr and so on. This is typically 10 times longer for each 25^°C reduction in temperature, so, when operating at 100^°C, one can expect ageing of 0.1ppm over 10000hrs – approximately 60 weeks. If this is extrapolated, the device can be expected to age by 0.32ppm over a period of 10 years.

Circuit construction and layout
In a circuit where such a high level of accuracy is important, careful consideration of the power supply and ground return layout helps to ensure the rated performance. Design the pcb such that the analogue and digital sections are separated and confined to separate areas of the board.
There should be ample power supply bypassing of 10µF in parallel with 0.1µF on each supply located as close to the package as possible. The capacitors should have low effective series resistance and low effective series inductance. A series ferrite bead on each power supply line will further help to reduce high frequency noise getting through to the device.

The power supply lines should use as large a trace as possible to provide low impedance paths and to reduce the effects of glitches on the power supply line. Shield fast switching signals, such as clocks, with digital grounds to avoid radiating noise to other parts of the board; they should never be run near the reference inputs or under the package. Avoid crossover of digital and analogue signals and run traces on opposite sides of the board at right angles to each other to reduce the effects of feedthrough on the board.

Building a 1ppm a/d solution
A typical contemporary 1ppm a/d solution consists of two 16bit d/a converters – one major, the other minor. Their outputs are scaled and combined to yield increased resolution. The output from the major d/a converter is summed, with the output from the minor device attenuated so that it fills the resolution gaps between the major d/a converter’s LSB steps.

The combined outputs need to be monotonic, but not extremely linear, because high performance is achieved with constant voltage feedback via a precision a/d converter, which corrects for the inherent component errors. Thus, circuit accuracy is limited by the a/d converter, rather than the d/a converters. However, because of the requirement for constant voltage feedback and the inevitable loop delay, the solution is slow, potentially requiring seconds to settle.

Digital circuitry is also needed to facilitate the interface between both d/a converters and the a/d converter; not to mention the software required for error correction.

Author profile:
Maurice Egan is a product applications engineer for precision converter products with Analog Devices.