Embedded Systems Design - July 2008 - (Page 34)

feature By designing a circuit with off-the-shelf components that obtains a quiescent current of 5 mA, we have surpassed our goal of 12 mA. Efficiency for the Figure 3 power supply is relatively flat for different loads at the nominal Vin of 12 V. 100% 80% 60% Javier Monsalve Kägi graduated with a BSEE and MSEE from Worcester Polytechnic Institute, Massachusetts. He is a ﬁeld applications engineer at Maxim Integrated Products, Inc., and previously worked for Spanish companies doing analog and digital electronic design in avionics and designing an IC for temperature measurement and voice synthesis (thermometer for the visual impaired). You may reach him at javier.monsalve@maxim-ic.com. ENDNOTES: 1. Carney, William. “IEEE 902.11g: New Draft Standard Clarifies Future of WLAN,” Texas Instruments Inc., 2002. PDF available on http://focus.ti.com/docs/ solution/folders/print/47.html. Haroun, Ibrahim, Ioannis Lambadaris, and Roshdy Hafez. “RF System Issues in Wireless Sensor Networks,” Microwave Engineering Europe, Nov. 2005, pp. 31–35. PDF available on www.mwee.com/ mag_archive/mwee1105.html. Application Note 664, “Feedback Isolation Augments Power-Supply Safety and Performance,” Maxim Integrated Products, Jan 22, 2001 (see www.maximic.com/an664). Also see June 19, 1997 issue of EDN (www.edn.com/archives/ 1997/061997/13df_04.htm). Garate, Jose Ignacio, Jose Miguel de Diego, and Maite Sierra. “Consequences of Discontinuous Current Consumption on Battery Powered Wireless Terminals,” [ISIE06, Paris, France, Oct. 2006]. IEEE Explore: http://ieeexplore.ieee.org/xpl/ freeabs_all.jsp?arnumber=4153462 Garate, Jose Ignacio and Jose Miguel de Diego. “Improvements of Power Supply Systems in Machine to Machine Modules and Fixed Cellular Terminals with Discontinuous Current Consumption,” (Digests 9th ICIT06, Mumbai, India, Dec. 2006.) n (%) 2. 40% 20% 0% 0 0.14 0.2 0.3 0.4 0.5 Io ( A ) 0.6 0.7 0.8 0.9 1 3. Figure 5 techniques described in two papers by Jose Ignacio Garate and others.4, 5 A capacitor of high value and low ESR is highly recommended. Measurement results (Tables 2 and 3) don’t include losses in the common-mode input filter or the protection circuitry. Table 2 gives values for the power supply’s input and output variables for different input voltages under no-load conditions. The minimum current draw achieved is 5 mA. You can reduce that to 3 mA, but the low-value resistor necessary to achieve 3 mA causes the control loop to become unstable. To prevent self oscillation and to accommodate component tolerances, a security margin is introduced by setting the current draw slightly higher than 5 mA. As shown in Table 3, the optimum efficiency is reached at normal conditions with a nominal load. Figure 5 shows the efficiency for different output currents. For commercially available, isolated power supplies with similar characteristics, we found that the lowest no34 load current draw is around 20 mA. By designing a circuit with off-the-shelf components that obtains a quiescent current of 5 mA, we have surpassed our goal of 12 mA. ■ Jose Miguel de Diego has a BS in electrical engineering from the E.T.S.I.I. of Navarra University, San Sebastián, and a doctorate in industrial engineering from the High School of Engineering of Bilbao, Spain. His research areas are power-supply systems and renewable energies, and he has worked in R&D at industrial electronics companies, including Ericsson Radio S.A., Spain. You may reach him at jm.dediego@ehu.es. Jose Ignacio Garate has a BS and an MS degrees from the High School of Engineering of Bilbao, Spain, both in telecommunication engineering. He is working on his doctorate on discontinuous current consumption in battery-powered wireless terminals and output power control for radio-frequency power ampliﬁers. He worked in the R&D departments of Ericsson Radio S.A., Spain, and Ericsson ABB, Lund and Gable, Sweden. You may reach him at joseignacio.garate@ehu.es. 4. 5. FURTHER READING: “MAX1649/MAX1651, 5V/3.3V or Adjustable, High-Efﬁciency, Low-Dropout, Stepdown DCDC Controllers,” Maxim Integrated Products, Datasheet 10-0305, Rev 2; 9/95. www.maxim -ic.com/quick_view2.cfm/qv_pk/1028 “MAX1771, 12V or Adjustable, High-Efﬁciency, Low IQ, Step-Up DC-DC Controller,” 2002, Maxim Integrated Products, Datasheet 190263; Rev 2; 3/02. www.maxim-ic.com/quick _view2.cfm/qv_pk/1030 JULY 2008 | embedded systems design | www.embedded.com http://focus.ti.com/docs/solution/folders/print/47.html http://focus.ti.com/docs/solution/folders/print/47.html http://www.mwee.com/mag_archive/mwee1105.html http://www.mwee.com/mag_archive/mwee1105.html http://www.maximic.com/an664 http://www.maximic.com/an664 http://www.edn.com/archives/1997/061997/13df_04.htm http://www.edn.com/archives/1997/061997/13df_04.htm http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=4153462 http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=4153462 http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1028 http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1028 http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1030 http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1030 http://www.embedded.com

Table of Contents Feed for the Digital Edition of Embedded Systems Design - July 2008

Embedded Systems Design - July 2008 Contents #Include Parity Bit Programming Pointers Interactive C-code Cleaning Tool Supports Multiprocessor SoC Design Building a Power Supply for Discontinuous Transmission Wireless Networks An Exception Primer Advertising Index Break Points Marketplace

Embedded Systems Design - July 2008

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