aroma of burning circuit board in the earlier days of their career. When time is short or power supply design experience is limited, the readymade µModule regulator saves time and reduces risk to the program.
Developments of newer multi-output
products have added to the attractiveness. Figure 4 indicates the simplicity of a 4-channel solution based on the LTM4644 which is packaged in a 9mm x 15mm x 5.01mm BGA and can be configured with channels in parallel where needed. The external component count amounts to a single resistor to set
each output voltage accompanied by bulk input and output capacitors. A further advantage of the flexible output configuration is the opportunity to reduce the number of part types qualified on the corporate preferred parts listing, saving component engineering resources and increasing purchase quantities.
Safety and reliability Interconnect reliability of Bottom Termination Components (BTC) has long been an industry concern and many in- house studies at major defence contractors have been conducted to
determine the environmental suitability of different BTC package types. Linear Technology has also conducted studies where daisy-chain connected products are temperature cycled for many thousands of hours to determine solder interconnect reliability. Since the introduction of the first µModule regulator, LTM4600 in LGA packaging with gold plated square pads, much work has been undertaken to improve the physical layout of pads and internal design features. BGA packaging has been introduced and customers are provided with the option of SAC305 or SnPb ball composition. The later option is key for many military systems where in very harsh environments the use of SnPb components is still preferred, particularly for BTCs.
Designing for safety critical applications has also been assisted by the feature set of newer products, for example by returning to the LTM4644 Quad 4A µModule regulator discussed earlier the following features are provided: • Internal temperature sensing is
Figure 4: LTM4644 Quad 4A µModule Regulator with configurable output array
provided by a diode connected PNP transistor with a temperature coefficient equal to about -2mV/°C, this can be connected to an external ADC to provide data for the control system.
• Over temperature protection monitors the junction temperatures in the module. If the junction temperature reaches approximately 160°C the output will be turned off until the temperature drops about 15°C cooler. • Overcurrent and overvoltage fault conditions are protected by internal circuitry that performs foldback current limiting and monitors the output feedback voltage within a ±10% window around the regulation point. Other safety features that can be found
across the product range include adjustable input and output average current limits, input and output current monitors and full digital interface and control with onboard EEPROM for fault logging.
Conclusion
Advances in semiconductor and package technology have led to continuous improvement of products - in particular this article has focused on µModule regulator solutions and how they can help designers meet new performance goals in terms of improvements in solution SWaP and reliability, shorter time to market with lower risk, and optimum use of design teams and support resources
www.linear.com
www.cieonline.co.uk
Components in Electronics
May 2015 11
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