SLOA198A September   2014  – December 2021 DRV2665 , DRV2667 , DRV2700 , DRV8662

 

  1.   Trademarks
  2. 1 Boost Converter Basics
  3. 2 DRV8662, DRV2700, DRV2665, and DRV2667 Boost Converter
    1. 2.1 DRV8662, DRV2700, DRV2665, and DRV2667 Boost Converter Efficiency
      1. 2.1.1 Boost Efficiency vs Boost Current
    2. 2.2 DRV8662, DRV2700, DRV2665, and DRV2667 Boost Converter Load Regulation
      1. 2.2.1 Boost Regulation vs Current
  4. 3 Configuring the Boost Converter
  5. 4 Boost Converter Output Voltage
  6. 5 Calculating the Load Current
  7. 6 Selecting an Inductor
    1. 6.1 Inductance Rating
    2. 6.2 Saturation Current Rating
    3. 6.3 Thermal Current Rating
    4. 6.4 Choosing REXT
    5. 6.5 What to Avoid: Using Incorrect Inductor Current Ratings
  8. 7 Calculate the Maximum Boost Current
  9. 8 Output Capacitor Selection
  10. 9 Input Capacitor Selection
  11. 10PCB Layout
    1. 10.1 What to Avoid: Incorrect Inductor Placement
  12. 11Examples
    1. 11.1 Example: Based on the DRV8662EVM
      1. 11.1.1 Configure the Boost Voltage
      2. 11.1.2 Configure the Inductor Current
      3. 11.1.3 Boost Performance Results
    2. 11.2 Example: Based on the DRV2667EVM-CT with 25-nF Piezo Module
      1. 11.2.1 Configure the Boost Voltage
      2. 11.2.2 Configure the Inductor Current
      3. 11.2.3 Boost Performance Results
  13. 12Revision History

6.1 Inductance Rating

The inductance sets the maximum switching frequency of the boost converter. The general trade off with inductances between 3.3 µH and 22 µH are:

  • Larger inductances (10 µH or greater)
    • Advantage: Cause the boost converter to run at a lower switching frequency meaning less switching losses.
    • Disadvantage: Larger values typically have higher series resistance and lower saturation currents, requiring physically larger inductors.
  • Smaller inductances (Less than 10 µH)
    • Advantage: Typically have higher saturation currents and are a better choice for maximizing output current of the boost converter per inductor area.
    • Disadvantage: Higher switching frequencies can lead to more losses. Switching losses are not a major concern in most applications, but if thermal dissipation is a concern because of a small PCB or extreme temperatures, then consider using a larger inductance.

The approximate switching frequency can be calculated using Equation 4:

Equation 4. GUID-1C15A373-6621-46F6-8D80-1FF2027BED3A-low.gif
SymbolDescriptionValueUnit
fswitchingDRVxxx switching frequency–Hz
VINMinimum VDD voltage applied to the DRVxxxx–V
VBOOSTMaximum boost output voltage–V
ILIMITCurrent limit set by the DRVxxxx REXT resistor–Ap
Tip
Smaller inductances (3.3 – 4.7 µH) are often preferred in space-constrained applications because of their size, higher saturation current, and ability to deliver more charge to the load.