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17_W_5_V_AND_33_V_POWER_SUPPLY

2015-03-20 07:30  
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17_W_5_V_AND_33_V_POWER_SUPPLY
The low concerns of today's notebook computer designs do not have to restrict designers to low-performance solutions. The logic power supply is usually required to furnish excellent regulation at extremely high efficiency, but also carry a small price tag. This LTC1149 circuit addresses these requirements by using a single synchronous rectifier controller IC to generate both 3.3- and 5-V logic supplies. The 3.3-V output is generated in normal step-down regulator fashion using synchronous switches and an inductor. The key to circuit operation is the extra winding on the inductor and its corresponding synchronous rectifier, QN2. These provide the 5-V output by using transformer action. Cross regulation with this circuit is excellent because of the use of a trifilarwound inductor and a split feedback, which combines both outputs into the same feedback net-work. Efficiency exceeds 90 percent over most of the operating range. In addition, the 3.3- and 5-V outputs are inherently synchronous in switching frequency, and they will reach their rated voltage at the same time after power-up. Another bonus is that is if one logic supply is short-circuited, the other output will be disabled.