TPS54521

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SLVS981C – JUNE 2010 – REVISED AUGUST 2013

Table 2. Bill of Materials (continued)

COUNT

RefDes

Value

Description

Size

Part Number

MFR

IC, 17V Input, 5A Output, Sync. Step Down

1

U1

TPS54521RHL

QFN14

TPS54521RHL

TI

Switcher With Integrated FET

PCB Layout Guidelines

Layout is a critical portion of good power supply design. See Figure 55 for a PCB layout example. The top layer

contains the main power traces for VIN, VOUT, and the PH node. Also on the top layer are connections for the

remaining pins of the TPS54521 and a large top side area filled with ground. The top layer ground area should

be connected to the internal ground layer(s) using vias at the input bypass capacitor, the output filter capacitor

and directly under the TPS54521 device to provide a thermal path from the exposed thermal pad land to ground.

The GND pin should be tied directly to the exposed thermal pad under the IC. For operation at full rated load, the

top side ground area together with the internal ground plane, must provide adequate heat dissipating area. There

are several signals paths that conduct fast changing currents or voltages that can interact with stray inductance

or parasitic capacitance to generate noise or degrade the power supply's performance. To help eliminate these

problems, the PVIN pin should be bypassed to ground with a low ESR ceramic bypass capacitor with X5R or

X7R dielectric. Care should be taken to minimize the loop area formed by the bypass capacitor connections, the

PVIN pins, and the ground connections. The VIN pin must also be bypassed to ground using a low ESR ceramic

capacitor with X5R or X7R dielectric. Make sure to connect this capacitor to the quiet analog ground trace rather

than the power ground trace of the PVIN bypass capacitor. Since the PH connection is the switching node, the

output inductor should be located close to the PH pins, and the area of the PCB conductor minimized to prevent

excessive capacitive coupling. The output filter capacitor ground should use the same power ground trace as the

PVIN input bypass capacitor. Try to minimize this conductor length while maintaining adequate width. The small

signal components should be grounded to the analog ground path as shown. The RT/CLK pin is sensitive to

noise so the RT resistor should be located as close as possible to the IC and routed with minimal lengths of

trace. The additional external components can be placed approximately as shown. It may be possible to obtain

acceptable performance with alternate PCB layouts. However, this layout has been shown to produce good

results and is meant as a guideline.

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