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 Selecting an Inductor

The inductor plays a critical role in the performance of the DRV8662, DRV2700, DRV2665, and DRV2667, so selecting and testing a suitable inductor is important to ensure the best performance.

An inductor can be described with relatively few parameters. The following table shows the typical parameters listed in an inductor datasheet:

Part NumberInductance
(µH)		DC Resistance
(Ω)		ISATURATION
(A)		IRMSSRF
(MHz)
CIG22E3R3SNE3.30.2001.11.3042
DEFINITIONS
Inductance – the primary functional parameter of an inductor.
DC Resistance (DCR) – the resistance in the inductor due to the wire
ISATURATION or Saturation Current – the peak current flowing through the inductor that causes the inductance to drop due to core saturation.
IRMS or RMS Current or Thermal Current – the amount of continuous RMS current flowing through the inductor that causes the maximum allowable temperature rise.
SRF or Self Resonant Frequency – the frequency at which the inductance of the inductor winding resonates with the capacitance of the inductor winding.

To help narrow the number of inductors quickly, begin by looking at these three parameters:

  1. Inductance – the range of recommend inductances is from 3.3 µH to 22 µH.
  2. Saturation Current (ISAT, 30% decrease in inductance due to DC current) – saturation current should typically be above 1 A for most applications, but will vary depending on the load. Use the examples at the end of this document as a reference for choosing an inductor.
  3. RMS Current or Thermal Limit – the RMS current is less of an issue for haptic applications because of the low duty cycle of operation; however, in other applications where continuous operation is likely, be sure to select an appropriate RMS current rating.

Inductor current ratings are always the biggest source of confusion when selecting an inductor, because there are multiple, non-standardized current ratings to look for. See Section 6.5 for more information on inductor current ratings.

See the following sections for more information on each parameter.

Note:

The inductor will see high voltages (VBST – VDD) during normal operation. Ideal inductors do not have a voltage rating and thus most manufacturers will not publish a voltage rating; however, certain inductor core materials have voltage limitations. Please contact the manufacturer and ensure that the inductor material can operate at high voltages.