OUT

OUT

IN

IN

L(peak)

OUT

I

V

V

V

D

I

=

+

with D =

2

f

L

(1

D)

η

V

-

´

´

´

-

´

(

)

´

-

»

D

´

´

IN

OUT

IN

MIN

L

OUT

V

V

V

L

I

f

V

»

´

´

OUT

L_MAX

OUT

IN

V

I

I

η

V

TPS61240, TPS61241

www.ti.com

SLVS806D – APRIL 2009 – REVISED DECEMBER 2015

10.2.2.1 Programming the Output Voltage

The output voltage is set by a resistor divider internally. The FB pin is used to sense the output voltage. So to

configure the output properly, the FB pin needs to be connected directly to the output.

10.2.2.2 Inductor Selection

To make sure that the TPS6124x devices can operate, an inductor must be connected between pin VIN and pin

L. A boost converter normally requires two main passive components for storing energy during the conversion. A

boost inductor and a storage capacitor at the output are required. To select the boost inductor, it is

recommended to keep the possible peak inductor current below the current limit threshold of the power switch in

the chosen configuration. The highest peak current through the inductor and the switch depends on the output

load, the input (VIN), and the output voltage (VOUT). Estimation of the maximum average inductor current can be

done using Equation 2.

(2)

For example, for an output current of 200 mA at 5.0 V VOUT, at least 540 mA of average current flows through the

inductor at a minimum input voltage of 2.3 V.

The second parameter for choosing the inductor is the desired current ripple in the inductor. Normally, it is

advisable to work with a ripple of less than 20% of the average inductor current. A smaller ripple reduces the

magnetic hysteresis losses in the inductor, as well as output voltage ripple and EMI. But in the same way,

regulation time at load changes rises. In addition, a larger inductor increases the total system size and cost. With

these parameters, it is possible to calculate the value of the minimum inductance by using Equation 3.

(3)

Parameter f is the switching frequency and

ΔIL is the ripple current in the inductor, i.e., 20% x IL. In this example,

the desired inductor has the value of 1.7

μH. With this calculated value and the calculated currents, it is possible

to choose a suitable inductor. In typical applications a 1.0-

μH inductance is recommended. The device has been

optimized to operate with inductance values between 1.0

μH and 2.2 μH. It is recommended that inductance

values of at least 1.0

μH is used, even if Equation 3 yields something lower. Care has to be taken that load

transients and losses in the circuit can lead to higher currents as estimated in Equation 3. Also, the losses in the

inductor caused by magnetic hysteresis losses and copper losses are a major parameter for total circuit

efficiency.

With the chosen inductance value, the peak current for the inductor in steady state operation can be calculated.

Equation 4 shows how to calculate the peak current I.

(4)

This would be the critical value for the current rating for selecting the inductor. It also needs to be taken into

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

Table 3. List of Inductors

MANUFACTURER

SERIES

DIMENSIONS

MDT2012-CH1R0AN

2.0 x 1.2 x 1.0 max. height

TOKO

MDT1608-CH1R0N

1.6 x 0.8 x 0.95 max. height

KSLI-201210AG-1R0

2.0 x 1.2 x 1.0 max. height

Hitachi Metals

KSLI-201610AG-1R0

2.0 x 1.6 x 1.0 max. height

muRata

LQM21PN1R0MC0

2.0 x 1.2 x 0.55 max. height

FDK

MIPS2012D1R0-X2

2.0 x 1.2 x 1.0 max. height

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