MB39A132QN-G-ERE1 Datasheet, PDF (46/56 Pages) Fujitsu Component Limited. – ASSP For Power Management Applications (Rechargeable Battery) Synchronous Rectification DC/DC Converter IC for Charging Li-ion Battery

MB39A132
• Board layout
When designing the layout, consider the points listed below. Take account of the following points when
designing the board layout.
- Place a GND plane on the IC mounting surface whenever possible. Connect bypass capacitors connected
to switching components to the switching GND (PGND pin), and controller components to GND (GND
pin). Separate different GND so that no large current path passes through the controller GND (GND pins).
When designing the connection of the controller GND and the switching GND, make their connection
underneath the IC. Connect PGND to the controller GND at only one point to prevent large current from
flowing to the controller GND. Connect the controller GND to PGND only at one point of PGND in order
to prevent a large current path from passing the controller GND.
- Connect to the input capacitor (CIN), SWFET, SBD, inductor (L), sense resistor (Rs), output capacitor (Co)
on the surface layer. Do not connect to them via any through-hole.
- For a loop composed of input capacitors (CIN), switching FET and SBD, minimize its current loop. When
minimizing routing and loops, give priority to this loop over others.
- Create through-holes directly next to the GND pins of the input capacitor (CIN), SBD, output capacitor
(Co), and connect these pins to the GND of the inner layer.
- Place the boot strap capacitor (CBOOT) as close to the CB, LX pins as possible.
- Place the input capacitor (CIN) and high-side FET as close together as possible. Bring out the net of the
LX pin from a point close to the source pin of the high-side FET. Large currents momentarily flow through
the net of the LX pin. Use a wiring width of about 0.8 mm, and minimize the length of routing.
- Large currents momentarily flow through the nets of the OUT1, OUT2 pins, which are connected to the
switching FET gate. Use a wiring width of about 0.8 mm and minimize the length of routing.
- Place the bypass capacitor connected to VCC, VIN, VREF, and VB pins, and the resistance connected
to the RT pin as close to the respective pins as possible. Moreover, connect the bypass capacitor and
the GND pin of the fOSC:setting resistance in close proximity to the GND pin of the IC.
(Strengthen the connection to the internal layer GND by making through-holes in close proximity to each
of the GND pin of the IC, terminals of bypass capacitors, terminals of the fosc setting resistors.)
- -INCx,+INCx, BATT,COMPx,RT pins is sensitive to noise. Therefore, minimize the routing of these pins
and keep them as far away from switching components as possible.
- The remote sensing (Kelvin connection) of the routing of the -INC2 and +INC2 pins are very sensitive to
noise. Therefore, make their routing close to each other and keep the routing as far away from switching
components as possible.
GND routing example
Example of switching components
High-side FET
PGND
VCC
VIN
To LX pin
Low-side FET
VIN
Cin
PGND
GND
VREF
RT
Connect the PGND to the GND at a single point
directly under the IC.
Surface layer
Inner layer
SBD
L
Co
VO
RS
To +INC2 pin
To -INC2 pin
To BATT pin
To feedback line
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DS04–27265–3E