(

)

OUT

OUT

IN

MIN

OUT

I

V

V

C

f

V

V

-

=

D

g

g

g

h

g

g

OUT

L(DC)

OUT

IN

V

1

I

=

I

V

OUT

IN

IN

L(PEAK)

OUT

I

V

D

V

I

=

+

with D

1

2

f

L

(1 D)

V

h

=

-

-

h

g

g

g

g

g

TPS61253, TPS61254, TPS61256, TPS61258, TPS61259

www.ti.com

SLVSAG8E – SEPTEMBER 2011 – REVISED MARCH 2015

(4)

Selecting an inductor with insufficient saturation performance can lead to excessive peak current in the

converter. This could eventually harm the device and reduce its reliability.

When selecting the inductor, as well as the inductance, parameters of importance are: maximum current rating,

series resistance, and operating temperature. The inductor DC current rating should be greater (by some margin)

than the maximum input average current, refer to Equation 5 and Current Limit Operation section for more

details.

(5)

The TPS6125x series of step-up converters have been optimized to operate with a effective inductance in the

range of 0.7 µH to 2.9 µH and with output capacitors in the range of 10 µF to 47 µF. The internal compensation

optimize the performance of the device for specific operating conditions. For more details, see the Checking

Loop Stability section.

In high-frequency converter applications, the efficiency is essentially affected by the inductor AC resistance (i.e.

quality factor) and to a smaller extent by the inductor DCR value. To achieve high efficiency operation, care

should be taken in selecting inductors featuring a quality factor above 25 at the switching frequency. Increasing

the inductor value produces lower RMS currents, but degrades transient response. For a given physical inductor

size, increased inductance usually results in an inductor with lower saturation current.

dependent components:

•

The losses in the core material (magnetic hysteresis loss, especially at high switching frequencies)

•

Additional losses in the conductor from the skin effect (current displacement at high frequencies)

•

Magnetic field losses of the neighboring windings (proximity effect)

•

Radiation losses

The following inductor series from different suppliers have been used with the TPS6125x converters.

Table 4. List of Inductors

SERIES

DIMENSIONS (in mm)

HITACHI METALS

KSLI-322512BL1-1R0

3.2 x 2.5 x 1.2 max. height

LQM32PN1R0MG0

3.2 x 2.5 x 1.0 max. height

MURATA

LQM2HPN1R0MG0

2.5 x 2.0 x 1.0 max. height

LQM21PN1R5MC0

2.0 x 1.2 x 0.55 max height

DFE322512C-1R0

3.2 x 2.5 x 1.2 max. height

TOKO

MDT2012-CLR1R0AM

2.0 x 1.2 x 0.58 max height

(1)

See Third-Party Products Disclaimer

10.2.2.2 Output Capacitor

For the output capacitor, it is recommended to use small ceramic capacitors placed as close as possible to 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, using a smaller ceramic capacitor in parallel to the large one is highly

To get an estimate of the recommended minimum output capacitance, Equation 6 can be used.

(6)

Where f is the switching frequency which is 3.5 MHz (typ.) and

ΔV is the maximum allowed output ripple.

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