SLVAFL5 September   2023 TPS61299

 

  1.   1
  2.   Abstract
  3.   Trademarks
  4. 1Introduction of Water Heater
  5. 2Low Voltage Start-up Boost Converter Introduction
    1. 2.1 General Introduction About TPS61299
    2. 2.2 Introduction about Traditional Start-up Process
    3. 2.3 Down Mode and Boost Mode Operation
  6. 3TPS61299 Ultra-low Voltage Start-up Design
    1. 3.1 Ultra Low Voltage Start-up Set up
    2. 3.2 The Way AVIN influence Start-up Process
    3. 3.3 The Way Vout Influence Start-up Process
    4. 3.4 The Way L Influence Start-up process
      1. 3.4.1 Why With the Larger Inductance, The Smaller PVIN Start-up Can Be Achieved?
      2. 3.4.2 Why Does The Inductance Continue to Increase, The Minimum PVIN to Start Up Is Not Lower
      3. 3.4.3 Why 80 mV Can Start Normally While 70 mV Fail to?
  7. 4Ultra-low Voltage Start-up Design
    1. 4.1 Test Waveform
  8. 5Summary
  9. 6References

3.4.2 Why Does The Inductance Continue to Increase, The Minimum PVIN to Start Up Is Not Lower

The Ton_max of the low side MOSFET limits the excitation time of the inductor, so after inductance exceeds a certain value, VOUT remains unchanged when the excitation time remains unchanged. The larger L is, the smaller the di/dt is. When the on time of low side MOSFET reaches Ton_max , peak current of the inductor hasn't reached hysteresis current (350 mA) , then the low side MOSFET is forced to turn off, after which the high side MOSFET turns on. Therefore less energy is converted , so VOUT cannot be regulated to target voltage normally.

GUID-20230822-SS0I-SXB4-NB52-J5HV0LSVGWFQ-low.svg Figure 3-7 Inductor Current With Larger Inductance