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 is the 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 ns. Use the maximum input voltage and maximum efficiency to determine the

minimum duty cycle, Dmin. Use the maximum switching frequency for fSW.

min

_ min

_ max

ON

SW

D

t

f

(4)

then

• If tON_min min < 70 ns with 2.2 MHz, use 1 MHz.

• If tON_min min < 70 ns with 1 MHz, reduce the maximum input voltage.

• If tON_min min ≥ 70 ns for both cases, use 1 MHz for highest efficiency, or 2.2 MHz for lowest noise and ripple.

8.2.2.2.2 Output Capacitor Selection

The effective output capacitance can range from 40 μF (minimum) up to 200 μF (maximum) for a single L-C

system design. When using a second L-C filter, the first L-C filter must have output capacitance between 40

μF and 80 μF, the second stage L-C filter (if used) must have at least 20 μF of capacitance, and the total

capacitance for both L-C filters must be less than 200 μF. Load transient testing and measuring the bode plot are

good ways to verify stability.

TI recommends ceramic capacitors (X5R or X7R). Ceramic capacitors have a DC-Bias effect, which has a strong

influence on the final effective capacitance. Choose the right capacitor carefully in combination with considering

its package size and voltage rating. The ESR and ESL of the output capacitor are also important considerations

in selecting the output capacitors for low noise applications. Smaller package sizes typically have lower ESL

and ESR. 0805 or smaller packages are recommended, as long as they provide the required capacitance and

voltage rating for stable operation. Table 8-4 lists recommended output capacitors.

Table 8-4. Recommended Output Capacitors

CAPACITOR TYPE

CAPACITOR VALUE

MANUFACTURER

VOLTAGE (V)

PACKAGE

Bulk Capacitor

22 μF, X7S

TDK C2012X7S1A226M125AC

10

0805

Bulk Capacitor

47 μF, X7R

Murata GRM32ER71A476ME15L

10

1210

TPSM82913

SLVSGJ4A – OCTOBER 2022 – REVISED DECEMBER 2022

www.ti.com

22

Submit Document Feedback

Copyright © 2022 Texas Instruments Incorporated

Product Folder Links: TPSM82913