Datasheet

TPS54231

SLUS851C –OCTOBER 2008–REVISED JULY 2012

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Where:

Ptot is the total device power dissipation (W).

is the ambient temperature (°C).

is the junction temperature (°C) .

Rth is the thermal resistance of the package (°C/W).

JMAX

is maximum junction temperature (°C).

AMAX

is maximum ambient temperature (°C).

PCB LAYOUT

The VIN pin should be bypassed to ground with a low ESR ceramic bypass capacitor. Care should be taken to

minimize the loop area formed by the bypass capacitor connections, the VIN pin, and the anode of the catch

diode. The typical 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 source of the anode of the catch diode. See Figure 13 for

a PCB layout example. The GND D pin should be tied to the PCB ground plane at the pin of the IC. The source

of the low-side MOSFET should be connected directly to the top side PCB ground area used to tie together the

ground sides of the input and output capacitors as well as the anode of the catch diode. The PH pin should be

routed to the cathode of the catch diode and to the output inductor. Since the PH connection is the switching

node, the catch diode and output inductor should be located very close to the PH 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 TPS54231 uses a fused lead frame so that the

GND pin acts as a conductive path for heat dissipation from the die. Many applications have larger areas of

internal or back side ground plane available, and the top side ground area can be connected to these areas

using multiple vias under or adjacent to the device to help dissipate heat. The additional external components

can be placed approximately as shown. It may be possible to obtain acceptable performance with alternate

layout schemes, however this layout has been shown to produce good results and is intended as a guideline.