The WEBENCH Power Designer provides a customized schematic along with a list of materials with real-time

pricing and component availability.

In most cases, these actions are available:

• Run electrical simulations to see important waveforms and circuit performance

• Export customized schematic and layout into popular CAD formats

• Print PDF reports for the design, and share the design with colleagues

Get more information about WEBENCH tools at www.ti.com/WEBENCH.

8.2.2.2 External Component Selection

8.2.2.2.1 Switching Frequency Selection

The switching frequency can be chosen to optimize efficiency (1 MHz) or ripple/noise (2.2 MHz). Using the 2.2-

MHz setting increases the gain of the feedback loop and can result in lower output noise. However, additional

considerations for minimum on-time and duty cycle must also be considered. First, calculate the duty cycle using

Equation 3. Higher efficiency results in a shorter on-time, so a conservative approach is to use a higher

efficiency than expected in the application.

OUT

IN

V

D

V

K

u

(3)

where:

• η = estimated efficiency (use the value from the efficiency curves or 0.9 as an conservative assumption)

Then, calculate the on-time with both 1 MHz and 2.2 MHz using Equation 4. The on-time must always remain

above the minimum on-time of 70 nsec. Use the maximum input voltage and maximum efficiency to determine

min

_ min

_ max

ON

SW

D

t

f

(4)

then

8.2.2.2.2 Inductor Selection for the First L-C Filter

The inductor selection is dependent on the selected switching frequency and the duty cycle. When using the 2.2-

MHz frequency, only use a 2.2-µH inductor. When using the 1-MHz frequency, calculate the maximum duty cycle

V, use a 4.7-µH inductor to achieve the full output current or a 2.2-µH inductor for higher efficiency with a

reduced maximum output current.

The inductor also has to be rated for the appropriate saturation current. Equation 5 and Equation 6 calculate the

maximum inductor current under static load conditions. The formula takes the converter efficiency into account.

The calculation must be done for the maximum input voltage where the peak switch current is highest.

1

OUT

OUT

IN

L

SW

V

V

V

I

f

L

K

K

§

·

u¨

¸

u

©

¹

'

u

(5)

TPS62912, TPS62913

SLVSFP4 – AUGUST 2020

www.ti.com

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