´

>

´

OUT

OUT

IN

V

I

0.8

100 mA

V

´

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

´

´

´

IN

OUT

IN

OUT

V

(V

- V )

1

L =

f 200 mA

V

æ

ö

ç

÷

è

ø

OUT

FB

V

R

= R

x

- 1

1

2

V

TLV61220

www.ti.com

SLVSB53A – MAY 2012 – REVISED DECEMBER 2014

11.2.2.1 Adjustable Output Voltage Version

An external resistor divider is used to adjust the output voltage. The resistor divider needs to be connected

between VOUT, FB and GND as shown in Figure 14. When the output voltage is regulated properly, the typical

voltage value at the FB pin is 500 mV. The maximum recommended value for the output voltage is 5.5 V. The

current through the resistive divider should be about 100 times greater than the current into the FB pin. The

typical current into the FB pin is 0.01

μA, and the voltage across the resistor between FB and GND, R2, is

typically 500 mV. Based on those two values, the recommended value for R2 should be lower than 500 kΩ, in

order to set the divider current to 1

μA or higher. The value of the resistor connected between VOUT and FB, R1,

depending on the needed output voltage (VOUT), can be calculated using Equation 1:

(1)

As an example, if an output voltage of 3.3 V is needed, a 1-M

Ω resistor is calculated for R1 when for R2 a 180-kΩ

has been selected.

11.2.2.2 Inductor Selection

To make sure that the TLV61220 can operate, a suitable inductor must be connected between pin VBAT and pin

SW. 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.

(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.

(3)

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 helps 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.

(4)

The following inductor series from different suppliers have been used with TLV61220 converters:

Table 4. List of Inductors

VENDOR

INDUCTOR SERIES

Toko

DFE252010C

EPL3015

Coilcraft

EPL2010

Murata

LQH3NP

Taiyo Yuden

NR3015

Wurth Elektronik

WE-TPC Typ S

Copyright © 2012–2014, Texas Instruments Incorporated

Submit Documentation Feedback

13

Product Folder Links: TLV61220