SLVSDS9D July   2018  – January 2021

PRODUCTION DATA

1. Features
2. Applications
3. Description
4. Revision History
5. Description (continued)
6. Device Comparison Table
7. Pin Configuration and Functions
8. Specifications
9. Detailed Description
1. 9.1 Overview
2. 9.2 Functional Block Diagram
3. 9.3 Feature Description
4. 9.4 Device Functional Modes
1. 9.4.1 Peak-Current Mode Architecture
2. 9.4.2 Power Save Mode Operation
10. 10Application and Implementation
1. 10.1 Application Information
2. 10.2 Typical Application
11. 11Power Supply Recommendations
12. 12Layout
13. 13Device and Documentation Support
14. 14Mechanical, Packaging, and Orderable Information

• YFF|15

#### 10.2.2.2 Inductor Selection

The inductor selection is affected by several parameters such as the following:

• Inductor ripple current
• Output voltage ripple
• Transition point into power save mode
• Efficiency

See Table 10-3 for typical inductors.

For high efficiencies, the inductor must have a low DC resistance to minimize conduction losses. Especially at high-switching frequencies, the core material has a high impact on efficiency. When using small chip inductors, the efficiency is reduced, mainly due to higher inductor core losses. This needs to be considered when selecting the appropriate inductor. The inductor value determines the inductor ripple current. The larger the inductor value, the smaller the inductor ripple current and the lower the conduction losses of the converter. Conversely, larger inductor values cause a slower load transient response. To avoid saturation of the inductor, the peak current for the inductor in steady-state operation is calculated using Equation 2. Only the equation which defines the switch current in boost mode is shown because this provides the highest value of current and represents the critical current value for selecting the right inductor.

Equation 1.
Equation 2.

where

• D = Duty Cycle in Boost mode
• f = Converter switching frequency
• L = Inductor value
• η = Estimated converter efficiency (use the number from the efficiency curves or 0.9 as an assumption)
Note:

The calculation must be done for the minimum input voltage in boost mode.

Calculating the maximum inductor current using the actual operating conditions gives the minimum saturation current of the inductor needed. It is recommended to choose an inductor with a saturation current 20% higher than the value calculated using Equation 2. Table 10-3 lists the possible inductors.

Table 10-3 List of Recommended Inductors
INDUCTOR VALUE [µH] SATURATION CURRENT [A] DCR [mΩ] PART NUMBER MANUFACTURER(1) SIZE (LxWxH mm)
0.47 5.4 7.6 XFL4015-471ME Coilcraft 4 x 4 x 2
0.47 5.5 26 DFE201612E Toko 2.0 x 1.6 x 1.2