bd9876efj ROHM Co. Ltd., bd9876efj Datasheet - Page 9

• Manufacturer Part Number: bd9876efj
• Description: Flexible Step-down Switching Regulator With Built-in Power Mosfet
• Manufacturer: ROHM Co. Ltd.

●Evaluation Board Pattern (Reference)
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BD9876EFJ
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© 2011 ROHM Co., Ltd. All rights reserved.
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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.
Resistor
Divider
Inductor
Output
VOUT
Catch
Diode
Capacitor
Output
Fig.28 Evaluation Board Pattern
LX
GND
FB
VC
9/16
SYNC
VCC
BST
EN
Topside
Ground
Area
CBST
Input Bypass
Capacitor
Signal VIA
Thermal VIA
Route BST Capacitor
Trace on another layer to
provide with wide path for
topside ground
VCC
Technical Note
2011.07 - Rev.B