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PCB Layout Guidelines for Power Controllers
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Short Description: on the controllers comparator input voltage, the circuit design and layout must .... Following a basic set of power rules will reduce test time and time to ...
Content Inside: Application Report SLUA366 October 2005 PCB Layout Guidelines for Power Controllers Bob Kando .............................................................................................. PMP - Systems Power (MAN) 1 Scope Power layouts require a few basic rules. This guideline for power controller layout addresses: · The supply of sufficient current to the load. · Noise immunity for the load and sense circuits. · Accurate current sensing. Reference the controller datasheet for helpful applications information such as component selection, set point calculations and thermal considerations. The power controller datasheet may have specific bypass capacitor information. Other times it may be necessary to perform system measurements and tests to determine the optimum bypass values. Treatment of other high frequency system signals such as clocks are not discussed here and usual good practice rules for layout and manufacturability apply. 2 Description 2.1 General The power controller, MOSFET and sense resistor operate together to deliver power to the slot. These components should be located together at the slot. The sense resistor is sized to select the current supplied on a given slot voltage. Because of the tolerance on the controllers comparator input voltage, the circuit design and layout must consider the high end of the current range for etch runs and vias. A circuit that is design for 12 A minimum, often supplies current to a maximum of 18 A. Use 18 A for all the etch and via calculations. 2.2 PCB Etch Table 1 is helpful to determine the current carrying capacity of PCB etches. The table assumes: · 1oz/sq foot copper (0.035mm thickness). · 10°C rise on outer layers, 20°C inner layers · Groups of high current tracks are de-rated · Tracks are not near or over heat sink areas Table 1. Current Capacity PCB Etch WIDTH CURRENT CAPACITY 0.010" 0.8 A 0.015" 1.2 A 0.020" 1.5 A 0.050" 3.2 A 0.100" 6.0 A SLUA366 October 2005 PCB Layout Guidelines for Power Controllers 1 Document Outlineþÿþÿþÿþÿþÿþÿþÿþÿþÿþÿ
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