Inductor Selection

´

´

´

IN

OUT

IN

OUT

V

(V

- V )

1

L =

f 200 mA

V

(2)

´

ì

ï

´

í

ï

î

OUT

OUT

IN

L,MAX

V

I

+ 100 mA;

continous current operation

0.8 V

I

=

200 mA;

discontinuous current operation

(3)

´

>

´

OUT

OUT

IN

V

I

0.8

100 mA

V

(4)

Capacitor Selection

Input Capacitor

Output Capacitor

TPS61220

TPS61221

TPS61222

To make sure that the TPS6122x devices can operate, a suitable inductor must be connected between pin VIN

and pin L. Inductor values of 4.7

µH show good performance over the whole input and output voltage range .

Choosing other inductance values affects the switching frequency f proportional to 1/L as shown in Equation 2.

Choosing inductor values higher than 4.7

µH can improve efficiency due to reduced switching frequency and

therefore with reduced switching losses. Using inductor values below 2.2

µH is not recommended.

Having selected an inductance value, the peak current for the inductor in steady state operation can be

calculated. Equation 3 gives the peak current estimate.

For selecting the inductor this would be the suitable value for the current rating. It also needs to be taken into

account that load transients and error conditions may cause higher inductor currents.

Equation 4 provides an easy way to estimate whether the device will work in continuous or discontinuous

operation depending on the operating points. As long as the inequation is true, continuous operation is typically

established. If the inequation becomes false, discontinous operation is typically established.

The following inductor series from different suppliers have been used with TPS6122x converters:

Table 1. List of Inductors

VENDOR

INDUCTOR SERIES

EPL3015

Coilcraft

EPL2010

Murata

LQH3NP

Tajo Yuden

NR3015

Wurth Elektronik

WE-TPC Typ S

At least a 10-

µF input capacitor is recommended to improve transient behavior of the regulator and EMI behavior

of the total power supply circuit. A ceramic capacitor placed as close as possible to the VIN and GND pins of the

IC is recommended.

the VOUT and GND pins of the IC. If, for any reason, the application requires the use of large capacitors which

can not be placed close to the IC, the use of a small ceramic capacitor with an capacitance value of around

2.2

µF in parallel to the large one is recommended. This small capacitor should be placed as close as possible to

the VOUT and GND pins of the IC.

14

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