SLUSEG8B October 2021 – February 2022 LMR54406 , LMR54410

PRODUCTION DATA

- 1 Features
- 2 Applications
- 3 Description
- 4 Revision History
- 5 Device Comparison Table
- 6 Pin Configuration and Functions
- 7 Specifications
- 8 Detailed Description
- 9 Application and Implementation
- 10Power Supply Recommendations
- 11Layout
- 12Device and Documentation Support
- 13Mechanical, Packaging, and Orderable Information

- DBV|6

The most critical parameters for the inductor are
the inductance, saturation current, and the RMS current. The inductance is based on
the desired peak-to-peak ripple current Δi_{L}. Since the ripple current
increases with the input voltage, the maximum input voltage is always used to
calculate the minimum inductance L_{MIN}. Use Equation 9 to calculate the minimum value of the output inductor.
K_{IND} is a coefficient that represents the amount of inductor ripple
current relative to the maximum output current of the device. A reasonable value of
K_{IND} must be 20% to 60% of maximum I_{OUT} supported by
converter. During an instantaneous overcurrent operation event, the RMS and peak
inductor current can be high. The inductor saturation current must be higher than
peak current limit level.

Equation 8.

Equation 9.

In general, it is preferable to choose lower inductance in switching power supplies, because it usually corresponds to faster transient response, smaller DCR, and reduced size for more compact designs. Too low of an inductance can generate too large of an inductor current ripple such that overcurrent protection at the full load can be falsely triggered. It also generates more inductor core loss since the current ripple is larger. Larger inductor current ripple also implies larger output voltage ripple with the same output capacitors. With peak current mode control, it is recommended to have adequate amount of inductor ripple current. A larger inductor ripple current improves the comparator signal-to-noise ratio.

For this design example, choose K_{IND} = 0.4. The minimum inductor value is calculated to be 15.36 µH. Choose the nearest standard 15-µH ferrite inductor with a capability of 1.5-A RMS current and 2.5-A saturation current.