SLVAFD6 July   2022 TPS564247 , TPS565242

 

  1.   Abstract
  2.   Trademarks
  3. 1Introduction
  4. 2Analysis of the Floating-Input Pre-bias Output Operation
    1. 2.1 Analysis of FCCM Device
    2. 2.2 Analysis of PSM Device
  5. 3Experimental Verification
    1. 3.1 FCCM device
      1. 3.1.1 Bias Voltage > Target
      2. 3.1.2 Bias Voltage < Target
    2. 3.2 PSM device
      1. 3.2.1 Bias Voltage > Target
      2. 3.2.2 Bias Voltage < Target
  6. 4Summary
  7. 5References

4 Summary

For the floating input and bias output operation of the adaptive constant on-time (D-CAP) control device, the assessment of safe operation needs to discuss case by case. If the bias voltage is lower than UVLO threshold, device can operation safely both for FCCM and PSM device. If the bias voltage is higher than UVLO threshold, for FCCM device, it may encounter over voltage damage risk. Use enable function let device shut down is the most direct method to avoid energy flow into Vin side, but it is not the most simple method for PSM device. Based on the analysis in this application note, PSM device can operate safely if the bias voltage is higher than UVLO threshold. It means it is no need to use external control signal or switch, which can save the cost and system size.