www.ti.com
ꢀꢁ ꢂ ꢃꢄ ꢅꢃ ꢆ
SLVS456C − OCTOBER 2003 − REVISED OCTOBER 2004
APPLICATION INFORMATION
VIN
GND
VIN
BOOT
VOUT
VIN
PH
PH
UVLO
PWRGD
RT
LSG
VBIAS
PGND
AGND
VSENSE
SYNC
ENA
GND
COMP
VIA to Ground Plane
Figure 21. TPS54350 PCB Layout
PCB LAYOUT
The VIN pins should be connected together on the printed
circuit board (PCB) and bypassed with a low ESR ceramic
bypass capacitor. Care should be taken to minimize the
loop area formed by the bypass capacitor connections, the
VIN pins, and the TPS54350 ground pins. The minimum
recommended bypass capacitance is 10-µF ceramic with
a X5R or X7R dielectric and the optimum placement is
closest to the VIN pins and the AGND and PGND pins. See
Figure 21 for an example of a board layout. The AGND and
PGND pins should be tied to the PCB ground plane at the
pins of the IC. The source of the low-side MOSFET and the
anode of the Schottky diode should be connected directly
to the PCB ground plane. The PH pins should be tied
together and routed to the drain of the low-side MOSFET
or to the cathode of the external Schottky diode. Since the
PH connection is the switching node, the MOSFET (or
diode) should be located very close to the PH pins, and the
area of the PCB conductor minimized to prevent excessive
capacitive coupling. The recommended conductor width
from pins 14 and 15 is 0.050 inch to 0.075 inch of 1-ounce
copper. The length of the copper land pattern should be no
more than 0.2 inch.
For operation at full rated load, the analog ground plane
must provide adequate heat dissipating area. A 3-inch by
3-inch plane of copper is recommended, though not
mandatory, dependent on ambient temperature and
airflow. Most applications have larger areas of internal
ground plane available, and the PowerPAD should be
connected to the largest area available. Additional areas
on the bottom or top layers also help dissipate heat, and
any area available should be used when 3 A or greater
operation is desired. Connection from the exposed area of
the PowerPAD to the analog ground plane layer should be
made using 0.013-inch diameter vias to avoid solder
wicking through the vias. Four vias should be in the
PowerPAD area with four additional vias outside the pad
area and underneath the package. Additional vias beyond
those recommended to enhance thermal performance
should be included in areas not under the device package.
13
TI [ TEXAS INSTRUMENTS ]
