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

6.4 Choosing REXT

The resistor on the REXT pin is found using Equation 7:

Equation 7. GUID-EF8F957D-2EBE-4419-9836-6874EE3DC07B-low.gif
Symbol Description Value Unit
K 10500
VREF Internal reference voltage on REXT 1.35 V
RINT Internal resistance 60 Ω
ILIMIT Inductor current limit from inductor datasheet – Ap

The following graph shows the relationship between REXT and the current limit.

GUID-3BAD2725-4145-4D5E-A895-31E59A4B38E9-low.gif

Use the REXT resistor to set the current limit for the inductor. This can serve two purposes:

  1. Prevent Inductor Saturation – the current limit must be set equal to or lower than the inductor saturation current. If the inductance were to drop below 2.2 µH because of saturation, the boost converter may have difficulty regulating the output voltage.
  2. Limit Peak Battery Current – the resistor can help limit the maximum current from the battery; however, a lower current limit decreases the amount of current delivered to the load each switch cycle.
Tip
The best way to lower peak battery currents is by adding a bulk input capacitor.