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AAT1154 Datasheet(PDF) 12 Page - Advanced Analogic Technologies |
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AAT1154 Datasheet(HTML) 12 Page - Advanced Analogic Technologies |
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12 / 16 page  Layout Figures 2 and 3 display the suggested PCB layout for the fixed output AAT1154. The following guide- lines should be used to help ensure a proper layout. 1. The connection from the input capacitor to the Schottky anode should be as short as possible. 2. The input capacitor should connect as closely as possible to VP (Pins 5 and 8) and GND (Pin 2). 3. C1, L1, and CR1 should be connected as closely as possible. The connection from the cathode of the Schottky to the LX node should be as short as possible. 4. The feedback trace (Pin 1) should be separate from any power trace and connect as closely as possible to the load point. Sensing along a high-current load trace can degrade DC load regulation. 5. The resistance of the trace from the load return to GND (Pin 2) should be kept to a minimum. This will help to minimize any error in DC regu- lation due to differences in the potential of the internal reference ground and the load return. 6. R1 and C3 are required in order to provide a cleaner power source for the AAT1154 con- trol circuitry. Thermal The losses associated with the AAT1154 output switching MOSFET are due to switching losses and conduction losses. The conduction losses are associated with the RDS(ON) characteristics of the output switching device. At the full load condition, assuming continuous conduction mode (CCM), an accurate calculation of the RDS(ON) losses can be derived from the following equations: RDS(ON) losses Internal switch RMS current D is the duty cycle and VF is the forward drop of the Schottky diode. ΔI is the peak-to-peak inductor ripple current. A simplified form of calculating the RDS(ON) and switching losses is given by: where IQ is the AAT1154 quiescent current. Once the total losses have been determined, the junction temperature can be derived. The thermal resistance ( ΘJA) for the SOP-8 package mounted on an FR4 printed circuit board in still air is 110°C/W. TJ = P · ΘJA + TAMB TAMB is the maximum ambient temperature and TJ is the resultant maximum junction temperature. 2 O DS(ON) O IN IR V P = + tSW · FS · IO + IQ · VIN V · OF IN F VV D VV + = + 2 2 12 RMS O I II D ⎛⎞ Δ =+· ⎝⎠ 2 ON RMS DS(ON) PI R = · AAT1154 1MHz 3A Step-Down DC/DC Converter 12 1154.2006.09.1.6 Figure 2: AAT1154 Fixed Output Figure 3: AAT1154 Fixed Output Top Side Layout. Bottom Side Layout. |
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Similar Description - AAT1154 |
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