For all the applications, a 0.1 μF or higher value ceramic decoupling
capacitor is recommended between IN terminal and GND.
The optimum placement of
decoupling capacitor is closest to the IN and GND terminals of the device.
Care must be taken to minimize the loop area formed by the bypass-capacitor
connection, the IN terminal, and the GND terminal of the IC. See Figure 12-1 and Figure 12-2 for PCB layout examples with HTSSOP and VQFN packages respectively.
High current carrying power path connections must be as short as possible
and must be sized to carry atleast twice the full-load current.
RTN, which is the reference ground for the device must be a copper plane or
island.
Locate all the TPS26400
support components R(ILIM), C(dVdT),
R(IMON), and MODE, UVLO, OVP resistors close to their
connection pin. Connect the other end of the component to the RTN with
shortest trace length.
The trace routing for the RILIM and R(IMON) components
to the device must be as short as possible to reduce parasitic effects on
the current limit and current monitoring accuracy. These traces must not
have any coupling to switching signals on the board.
Protection devices such as TVS, snubbers, capacitors, or diodes must be
placed physically close to the device they are intended to protect, and
routed with short traces to reduce inductance. For example, a protection
Schottky diode is recommended to address negative transients due to
switching of inductive loads, and it must be physically close to the OUT and
GND pins.
Thermal Considerations: When
properly mounted, the PowerPAD package provides significantly greater
cooling ability. To operate at rated power, the PowerPAD must be soldered
directly to the board RTN plane directly under the device. Other planes,
such as the bottom side of the circuit board can be used to increase heat
sinking in higher current applications. Designs that do not need reverse
input polarity protection can have RTN, GND and PowerPAD connected together.
PowerPAD in these designs can be connected to the PCB ground plane.