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

8 Output Capacitor Selection

The output capacitor is important for decreasing output voltage ripple and reducing the effects of load transients on the boost voltage. The boost output voltage can be configured from 20 V up to 105 V, so the boost output capacitor must have a voltage rating equivalent to the boost output voltage or higher. A 250-V rated, 100-nF capacitor of X5R or X7R type is recommended for a boost converter voltage of 105 V. The selected capacitor should have a minimum working capacitance of 50 nF.

To estimate the absolute minimum capacitance required, use Equation 10. Typically the DRVxxxx devices operate with a switching frequency between 800 kHz to 1 MHz. To include additional margin for the device loop response, it is best to use one-sixth of the switching frequency (ƒ).

Equation 10. GUID-3E42979B-B33E-419D-9482-E706E96443F3-low.gif
Symbol Description Value Unit
DELTA I Boost transient current 0 – 0.070 mA
VDROOP Maximum boost output voltage droop – V
fSW Boost switching frequency Typically 800kHz-1MHz Hz
C Output capacitor – F
Tip
A guideline for ceramic capacitors: the de-rated capacitance is approximately equal to the rated capacitance multiplied by one minus the applied voltage over the rated voltage.
Cde-rated = Crated (1 – Vapplied/Vrated)
For example, when 50 V is applied to a 100-V rated capacitor, the capacitance will decrease by about 50%. Most capacitor vendors provide a capacitance versus voltage curve for reference.