BD9673AEFJ Datasheet, PDF (14/23 Pages) Rohm – Flexible Step-down Switching Regulators with Built-in Power MOSFET

BD9673AEFJ
Datasheet
●Evaluation Board Pattern (Reference)
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 VCC 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
VCC pin, and the anode of the catch diode. See Fig.28 for a PCB layout example. The GND pin should be tied directly to the
thermal pad under the IC and the thermal pad.
The thermal pad should be connected to any internal PCB ground planes using multiple VIAs directly under the IC. The LX
pin should be routed to the cathode of the catch diode and to the output inductor. 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. For operation at full rated load, the top side ground area must provide
adequate heat dissipating area. The additional external components can be placed approximately as shown. It may be
possible to obtain acceptable performance with alternate PCB layouts, however this layout has been shown to produce good
results and is meant as a guideline.
Figure 43. Evaluation Board Pattern
Figure 44. Reference Board Pattern
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TSZ22111・15・001
14/20
TSZ02201-0Q1Q0AJ00190-1-2
28.JAN.2014 Rev.003