AN3352

Layout guidelines

Doc ID 018526 Rev 3

21/26

3

Layout guidelines

Due to high current levels and fast switching waveforms, which radiate noise, a proper

printed circuit board (PCB) layout is essential. Sensitive analog grounds can be protected by

using a star ground configuration. Also, lead lengths should be minimized to reduce stray

capacitance, trace resistance, and radiated noise. Ground noise can be minimized by

connecting GND, the input bypass capacitor ground lead, and the output filter capacitor

ground lead to a single point (star ground configuration). Place input bypass capacitors (C1,

undervoltage protection circuitry, resetting the I²C internal registers. If this occurs, the

registers are set to zero and the LNBH24L is put into shutdown mode.

An LNB power supply demonstration board is available.

3.1

PCB layout

Any switch-mode power supply requires a good PCB layout in order to achieve maximum

performance. Component placement and GND trace routing and width, are the major

issues. Basic rules commonly used for DC-DC converters for good PCB layout should be

followed. All traces carrying current should be drawn on the PCB as short and as thick as

possible. This should be done to minimize resistive and inductive parasitic effects, and

increase system efficiency. White arrows indicate the suggested PCB (ring) ground plane to

avoid spikes on the output voltage (this is related to the switching side of the LNBH24L).

Good soldering of the ePad helps on this issue.

Figure 14.

PBC top layer