1

1

2

3

out

in

RMSCout

out

V

V

I

V

L

ƒ

-

=

´

´

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TPS62060, TPS62061, TPS62063

www.ti.com

SLVSA95B – MARCH 2010 – REVISED JULY 2015

9.2.2.2.2

Output Capacitor Selection

The advanced fast-response voltage mode control scheme of the TPS6206x allows the use of tiny ceramic

capacitors. Ceramic capacitors with low ESR values have the lowest output voltage ripple and are

recommended. The output capacitor requires either an X7R or X5R dielectric. Y5V and Z5U dielectric capacitors,

aside from their wide variation in capacitance over temperature, become resistive at high frequencies and may

not be used. For most applications a nominal 10 µF or 22 µF capacitor is suitable. At small ceramic capacitors,

the DC-bias effect decreases the effective capacitance. Therefore a 22 µF capacitor can be used for output

voltages higher than 2 V, see list of capacitors.

In case additional ceramic capacitors in the supplied system are connected to the output of the DC-DC converter,

range. In this case a loop stability analysis must be performed as described later.

At nominal load current, the device operates in PWM mode and the RMS ripple current is calculated as:

(8)

9.2.2.2.3

Input Capacitor Selection

Because of the nature of the buck converter having a pulsating input current, 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 VIN step on

the input can induce ringing at the VIN pin. This ringing can couple to the output and be mistaken as loop

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

Table 2. List of Capacitors

CAPACITANCE

TYPE

SUPPLIER

10

μF

GRM188R60J106M

0603: 1.6 x 0.8 x 0.8

Murata

22

μF

GRM188R60G226M

0603: 1.6 x 0.8 x 0.8

Murata

22 µF

CL10A226MQ8NRNC

0603: 1.6 x 0.8 x 0.8

Samsung

10 µF

CL10A106MQ8NRNC

0603: 1.6 x 0.8 x 0.8

Samsung

9.2.2.3 Checking Loop Stability

The first step of circuit and stability evaluation is to look from a steady-state perspective at the following signals

•

Switching node, SW

•

•

These are the basic signals that must be measured when evaluating a switching converter. When the switching

waveform shows large duty cycle jitter or the output voltage or inductor current shows oscillations, the regulation

loop may be unstable. This is often a result of board layout and/or wrong L-C output filter combinations. As a

next step in the evaluation of the regulation loop, the load transient response is tested. The time between the

application of the load transient and the turnon of the P-channel MOSFET, the output capacitor must supply all of

the device operates in PWM mode at medium to high load currents.

stability of the converter. Without any ringing, the loop has usually more than 45° of phase margin.

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