BD9E151NUX Datasheet, PDF (15/22 Pages) Rohm – 1ch Step-Down Switching Regulator

BD9E151NUX
Cautions on PCB board layout
TOP side
Ground Area
VCC
Datasheet
OUTPUT
Capacitor
Catch
Diode
VOUT
LX
SoftStart
Capacitor
Thermal VIA
Signal VIA
Figure 28. Reference PCB layout
Layout is a critical portion of good power supply design. There are several signals paths that conduct fast changing currents
or voltages that can interact with stray inductance or parasitic capacitance to generate noise or degrade the power supplies
performance. To help eliminate these problems, the VIN pin should be bypassed to ground with a low ESR ceramic bypass
capacitor with B dielectric. Care should be taken to minimize the loop area formed by the bypass capacitor connections, the
VIN pin, and the anode of the catch diode. See Fig.28 for a PCB layout example.
In the BD9E151NUX, since the LX connection is the switching node, the catch diode and output inductor should be located
close to the LX pins, and the area of the PCB conductor minimized to prevent excessive capacitive coupling. And GND area
should not be connected directly power GND, connected avoiding the high current switch paths. The additional external
components can be placed approximately as shown.
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TSZ22111・15・001
15/19
TSZ02210-0Q3Q0AZ00160-1-2
2013.07.17 Rev.001