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AME5284 Datasheet(PDF) 10 Page - Analog Microelectronics |
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AME5284 Datasheet(HTML) 10 Page - Analog Microelectronics |
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10 / 16 page  AME 10 AME5284 Rev.A.02 4A, 300KHz ~ 1.4MHz Synchronous Rectified Step-Down Converter Efficiency Considerations Although all dissipative elements in the circuit produce losses, one major source usually account for most of the losses in AME5284 circuits: I2R losses. The I2R loss dominates the efficiency loss at medium to high load currents. The I2R losses are calculated from the resistances of the internal switches, R SW, and external inductor R L. In continuous mode, the average output current flowing through inductor L is "chopped" between the main switch and the synchronous switch. Thus the series resistance looking into the SW pin is a function of both top and bottom MOSFET R DS(ON) and the duty cycle (D) as fol- lows: R SW = (RDS(ON)TOP)(D) + (RDS(ON)BOTTOM)(1-D) The R DS(ON) for both the top and bottom MOSFETs can be obtained from Electrical Characteristics table. Thus, to obtained I2R losses, simply add R SW to R L and multi- ply the result by the square of the average output cur- rent. Other losses including C IN and COUT ESR dissipative losses and inductor core losses generally account for less than 2% total additional loss. Thermal Considerations In most application the AME5284 does not dissipate much heat due to its high efficiency. But, in applications where the AME5284 is running at high ambient tempera- ture with low supply voltage and high duty cycles, such as in dropout, the heat dissipated may exceed the maxi- mum junction temperature of the part. If the junction temperature reaches approximately 170oC, both power switches will be turned off and the SW switch will be- come high impedance. |
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Similar Description - AME5284 |
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