In the previous article, we reviewed the current paths that accompany switching in a step-up DC/DC converter, as a basis for thinking about the PCB layout. In this article, prior to explaining specific issues, we describe the overall procedure for PCB layout, and indicate some important related points.
Procedure for PCB Layout of a Step-Up DC/DC Converter
The procedure for PCB layout is essentially as follows. The illustration provides a rough idea.
- 1.Position the input capacitors CIN and CIBYPASS near the IC.
- 2.To the extent possible, minimize the ground loops of the output capacitor COUT and the switching MOSFET.
- 3.Position the output capacitor COUT, the freewheel diode D2, and the inductor L as close together as possible, and on the same surface.
- 4.The area of the copper foil trace of the inductor L in particular should not be made greater than necessary, in order to diminish radiated emission from the switching node insofar as possible.
- 5.Thermal vias are provided as necessary.
- 6.The feedback path is laid out so as to recede from the vicinity of the output capacitor COUT and remain distant from noise sources such as the output capacitor COUT and the freewheel diode D2.
- 7.In some equipment, external compensation components RC and CC are necessary. Such components should be positioned close to the IC ground.
- 8.When a feedback voltage divider is necessary, it is positioned near the IC ground.
・The PCB layout is designed based on current paths in the circuit and the properties of the flowing currents.