SLVSB76B August   2012  – August 2019

PRODUCTION DATA.

1. Features
2. Applications
3. Description
1.     Device Images
4. Revision History
5. Pin Configuration and Functions
6. Specifications
7. Detailed Description
1. 7.1 Overview
2. 7.2 Functional Block Diagram
3. 7.3 Feature Description
4. 7.4 Device Functional Modes
8. Application and Implementation
1. 8.1 Application Information
2. 8.2 Typical Application
1. 8.2.1 Design Requirements
2. 8.2.2 Detailed Design Procedure
3. 8.2.3 Application Curves
9. Power Supply Recommendations
10. 10Layout
11. 11Device and Documentation Support
12. 12Mechanical, Packaging, and Orderable Information

• YFG|8

#### 8.2.2.1 Inductor Selection

For high efficiencies, the inductor should have a low DC resistance to minimize conduction losses. Especially at high-switching frequencies the core material has a higher 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, with the chosen inductance value, the peak current for the inductor in steady-state operation can be calculated. Only the equation which defines the switch current in boost mode is reported because this is providing 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 (typical 2 MHz)
• L = Selected inductor value
• η = Estimated converter efficiency (use the number from the efficiency curves or 0.80 as an assumption)
• ISW_MAX = Maximum average input current (Figure 6)

NOTE

The calculation must be done for the minimum input voltage which is possible to have in boost mode.

Consider the load transients and error conditions that can cause higher inductor currents. Consider when selecting an appropriate inductor. Please refer to Table 3 for typical inductors.

The size of the inductor can also affect the stability of the feedback loop. In particular the boost transfer function exhibits a right half-plane zero, whose frequency is inverse proportional to the inductor value and the load current. This means as higher the value of inductance and load current is the more possibilities has the right plane zero to be moved at lower frequency. This could degrade the phase margin of the feedback loop. TI recommends to choose the value of the inductor in order to have the frequency of the right half plane zero >400 kHz. The frequency of the RHPZ can be calculated using equation Equation 2.

Equation 3.

where

• D =Duty cycle in boost mode

NOTE

The calculation must be done for the minimum input voltage which is possible to have in boost mode.

### Table 3. Inductor Selection

INDUCTOR VALUE COMPONENT SUPPLIER SIZE (LxWxH mm) Isat/DCR
1 µH TOKO 1286AS-H-1R0M 2x1.6x1.2 2.3A/78mΩ
1 µH Coilcraft XFL4020-102 4 x 4 x 2.1 5.1A/10.8 mΩ
1 µH Coilcraft XFL3012-102 3 x 3 x 1.2 2.2 A/35 mΩ
1.5µH TOKO, 1286AS-H-1R5M 2 x 1.6 x 1.2 4.4A/ 14.40mΩ
1.5µH Coilcraft, LPS3015-152MLC 3 x 3 x 1.5 2.1A/100mΩ
1.5µH TOKO, 1269AS-H-1R5M 2.5 x 2 x 1 2.1A/108mΩ
2.2µH TOKO D1286AS-H-2R2M 2 x 1.6 x 1.2 1.6A/192mΩ