MB39C308 Datasheet, PDF (49/60 Pages) Fujitsu Component Limited. – 6ch DC/DC Converter IC for LPIA Platform VR

MB39C308
■ PRINTED CIRCUIT BOARD LAYOUT
Design of the PCB layout is important to make the suitable operation, suppressing noise or high efficiency ratio.
Refer to the evaluation board layout of MB39C308EVB-01 and consider the following guideline when designing
the layout of a circuit board.
1. Common items for each channel and peripheral components
• Ground and design for radiation of heat
At least, place the GND layer (PGND) in one of PCB internal layers. Place the through holes next to the GND
pin of IC and each component, and connect them to the GND layer with low impedance.
Place the AGND which is separated from the GND layer with flowing large current if possible. Connect the
bypass-capacitors of VREF and AVDD and the AGND pin of IC to the AGND. Connect AGND pin of IC to the
GND layer by one point connection as close as possible so as not to flow a large current to the AGND. Connect
GND pins of VB bypass-capacitor and the switching components to the GND layer directly.
Connect each thermal pin to the GND layer via the through hole so that the heat can be dissipated efficiency. It
is an ideal to place a through hole on a pad in the footprint of each thermal pin. Furthermore, it is also effective
to place the GND plane on the back side of the substrate of the trace mounted on IC.
• Bypass capacitors and boot strap capacitors
Place the bypass-capacitors connected to the VREF, AVDD, VB, PVDD7 pins next to each pin of IC. Furthermore,
connect the bypass-capacitors with the shortest path on surface layer to each pin. Place GND pins of bypass-
capacitors connected to VB and PVDD7 pins to the PGND7 pin with the shortest path.
Place the bootstrap capacitors for each channel next to CBx and LXx pins.
• Example layout
MB39C308
AVDD
VREF
CBx LXx
VB
PVDD7
x : Number of each channel
Pad of IC
Through hole
Capacitor
• Feedback line
Place the feed back lines to FB pins for each channel away from switching components and lines, because the
feed back line is sensitive to noise.
DS04-27261-6E
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