Datasheet

TPS62590

SLVS897B –JANUARY 2009– REVISED APRIL 2011

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Input Capacitor Selection

The buck converter has a natural pulsating input current; therefore, a low ESR input capacitor is required for best

input voltage filtering and minimizing the interference with other circuits caused by high input voltage spikes. For

most applications, a 10-μF ceramic capacitor is recommended. The input capacitor can be increased without any

limit for better input voltage filtering.

Take care when using only small ceramic input capacitors. When a ceramic capacitor is used at the input and the

power is being supplied through long wires, such as from a wall adapter, a load step at the output or V

step on

the input can induce ringing at the V

pin. The ringing can couple to the output and be mistaken as loop

instability or could even damage the part by exceeding the maximum ratings.

Table 5. List of Capacitor

CAPACITANCE TYPE SIZE SUPPLIER

10μF GRM188R60J106M69D 0603 1.6x0.8x0.8mm3 Murata

LAYOUT CONSIDERATIONS

As for all switching power supplies, the layout is an important step in the design. Proper function of the device

demands careful attention to PCB layout. Care must be taken in board layout to get the specified performance. If

the layout is not carefully done, the regulator could show poor line and/or load regulation, stability issues as well

as EMI problems. It is critical to provide a low inductance, impedance ground path. Therefore, use wide and

short traces for the main current paths. The input capacitor should be placed as close as possible to the IC pins

as well as the inductor and output capacitor.

Connect the GND Pin of the device to the Power Pad of the PCB and use this Pad as a star point. Use a

common Power GND node and a different node for the Signal GND to minimize the effects of ground noise.

Connect these ground nodes together to the Power Pad (star point) underneath the IC. Keep the common path

to the GND PIN, which returns the small signal components and the high current of the output capacitors as

short as possible to avoid ground noise. The FB line should be connected right to the output capacitor and routed

away from noisy components and traces (e.g., SW line).