LM5145 datasheet(27/55 Pages) TI

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9 Application and Implementation

Note

Information in the following applications sections is not part of the TI component specification,

and TI does not warrant its accuracy or completeness. TI’s customers are responsible for

determining suitability of components for their purposes, as well as validating and testing their design

implementation to confirm system functionality.

9.1 Application Information

9.1.1 Design and Implementation

To expedite the process of designing of a LM5146-based regulator for a given application, use the LM5146

Quickstart Calculator available as a free download, as well as numerous LM5146 reference designs populated in

TI Designs™ reference design library, or the designs provided in Section 9.2. The LM5146 is also WEBENCH®

Designer enabled.

9.1.2 Power Train Components

Comprehensive knowledge and understanding of the power train components are key to successfully completing

a synchronous buck regulator design.

9.1.2.1 Inductor

For most applications, choose an inductance such that the inductor ripple current, ΔIL, is between 30% and 40%

of the maximum DC output current at nominal input voltage. Choose the inductance using Equation 7 based on a

peak inductor current given by Equation 8.

OUT

˜ ¨

' ˜

(7)

L(peak)

OUT

(8)

Check the inductor data sheet to ensure that the saturation current of the inductor is well above the peak

inductor current of a particular design. Ferrite designs have very low core loss and are preferred at high

switching frequencies, so design goals can then concentrate on copper loss and preventing saturation. Low

inductor core loss is evidenced by reduced no-load input current and higher light-load efficiency. However, ferrite

core materials exhibit a hard saturation characteristic and the inductance collapses abruptly when the saturation

current is exceeded. This results in an abrupt increase in inductor ripple current, higher output voltage ripple,

not to mention reduced efficiency and compromised reliability. Note that the saturation current of an inductor

generally decreases as its core temperature increases. Of course, accurate overcurrent protection is key to

avoiding inductor saturation.

9.1.2.2 Output Capacitors

Ordinarily, the output capacitor energy store of the regulator combined with the control loop response are

prescribed to maintain the integrity of the output voltage within the dynamic (transient) tolerance specifications.

The usual boundaries restricting the output capacitor in power management applications are driven by finite

available PCB area, component footprint and profile, and cost. The capacitor parasitics—equivalent series

resistance (ESR) and equivalent series inductance (ESL)—take greater precedence in shaping the load transient

response of the regulator as the load step amplitude and slew rate increase.

The output capacitor, COUT, filters the inductor ripple current and provides a reservoir of charge for step-load

transient events. Typically, ceramic capacitors provide extremely low ESR to reduce the output voltage ripple

and noise spikes, while tantalum and electrolytic capacitors provide a large bulk capacitance in a relatively

compact footprint for transient loading events.

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LM5146

SNVSBV0A – JUNE 2021 – REVISED JUNE 2021

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