BD9B400MUV Datasheet, PDF (24/34 Pages) Rohm – Integrated MOSFET Single Synchronous Buck DC/DC Converter

BD9B400MUV
PCB Layout Design
In the step-down DC/DC converter, a large pulse current flows into two loops. The first loop is the one into which the current
flows when the High-Side FET is turned ON. The flow starts from the input capacitor CIN, runs through the FET, inductor L
and output capacitor COUT and back to GND of CIN via GND of COUT. The second loop is the one into which the current
flows when the Low-Side FET is turned on. The flow starts from the Low-Side FET, runs through the inductor L and output
capacitor COUT and back to GND of the Low-Side FET via GND of COUT. Route these two loops as thick and as short as
possible to allow noise to be reduced for improved efficiency. It is recommended to connect the input and output capacitors
directly to the GND plane. The PCB layout has a great influence on the DC/DC converter in terms of all of the heat
generation, noise and efficiency characteristics.
V_IN
C_IN
MOS FET
L
V_OUT
C_OUT
Figure 52. Current Loop of Buck Converter
Accordingly, design the PCB layout considering the following points.
 Connect an input capacitor as close as possible to the IC PVIN terminal on the same plane as the IC.
 If there is any unused area on the PCB, provide a copper foil plane for the GND node to assist heat dissipation from
the IC and the surrounding components.
 Switching nodes such as SW are susceptible to noise due to AC coupling with other nodes. Route the coil pattern as
thick and as short as possible.
 Provide lines connected to FB far from the SW nodes.
 Place the output capacitor away from the input capacitor in order to avoid the effect of harmonic noise from the input.
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TSZ02201-0J3J0AJ01200-1-2
22.Apr.2016 Rev.002