Design News, March 2013

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Electronics & Test module, the power is ready to be used. In portable applications such as cell phones, the output usually is used to charge a Lithium-Ion (Li-Ion) battery. Thus, a discrete battery charger is required. The charger uses the constant voltage from the receiver as an input power supply (figure 3). As described earlier, every sub-circuit within the wireless power receiver system contributes to power losses and affects efficiency. Design engineers are challenged by the efficiency of a wireless receiver, as well as thermal performance, board size, and BOM price of the portable device as a whole system. This implies that the battery charger within a portable device contributes to these challenging requirements, as well. One practical approach to lowering these requirements is to combine the rectification stage, voltage conditioning, and battery-charging circuits into one single IC for a highly efficient solution, versus a solution that uses a wireless power receiver followed by a separate downstream charger IC (figures 4 and 2) and expressed by equations 3 and 2, respectively. Equation 2: Efficiency (discrete solution %) = [(AC input Power)/(Vout*Iout)] * [(Vout*Iout)/ (VBAT*IBAT)] Equation 3: Efficiency (direct charging %) = (AC input Power)/(VBAT*IBAT) For example, the bq51050B provides all these functions in a single IC. This eliminates the need for a separate charger IC and provides potential cost savings in a small space-saving package. DN Tahar Allag is an analog power applications engineer with TI's single-cell battery management group where he is responsible for supporting external customers with detailed technical support for wired charging and wireless power-related problems. For more information, go to OTMC 100i Antenna-integrated PTP Grandmaster Clock • PTP Grandmaster Clock & NTP Time Server integrated in the antenna housing • Powered over Ethernet • Secure web interface • Extremely low power consumption More at: y to t wa g! ples in e sim sion Tim th eci lore Exp 1588 Pr IEEE

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