SDAA460 July   2026 ISOUSB211

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction
  5. 2Power Pins and Internal Rails
  6. 3Available Supply Options
    1. 3.1 Generating the 3.3V Rail (V3P3Vx)
    2. 3.2 Generating the 1.8V Rail (V1P8Vx)
    3. 3.3 Summary of the Four Building Blocks
  7. 4Typical Example Power Configurations
    1. 4.1 Power Configuration for an Isolated Host or Hub (Mixed Internal and External)
    2. 4.2 Power Configuration for Isolating a Self-Powered Peripheral
    3. 4.3 Power Configuration for Isolating a Bus-Powered Peripheral
  8. 5Thermal Considerations When Selecting a Supply Configuration
    1. 5.1 Operation Without External 1.8V Supply
    2. 5.2 Operation With External 1.8V Supply
  9. 6References
  10. 7Revision History

4.2 Power Configuration for Isolating a Self-Powered Peripheral

Figure 4-1 shows the equivalent arrangement for a self-powered peripheral. The roles of the two sides are mirrored relative to Figure 4-1:

  • Microcontroller side: V3P3V2 and VBUS2 are tied together to an external 3.3V supply. V1P8V2 is generated by the internal 1.8V LDO supplied from same external 3.3V supply on VCC2.
  • Connector side: VBUS1 is supplied by the VBUS of the USB port and the internal 3.3V LDO generates V3P3V1. The VCC1 and V1P8V1 are tied together to an external 1.8V supply derived from the same VBUS. For a peripheral, the total VBUS capacitance must stay below 10µF (at least 5µF recommended), with a 100nF capacitor close to the VBUS pin.
Isolated Self-Powered Peripheral with ISOUSB211 Figure 4-2 Isolated Self-Powered Peripheral with ISOUSB211