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 The Way L Influence Start-up process

Based on common sense, the lower power inductance may lead to more energy converting to the output side, regardless of the ripple and loop stability. However it is not all this case when DCR is taken into consideration, because larger DCR might lead to failure of starting up. This is a little different with how AVIN and VOUT influence start-up process, which is explained in detail.

Table 3-4shows the inductance and minimum PVIN which can achieve successful start-up, under the condition that VOUT=3.3 V, AVIN=0.7 V.

Table 3-4 Minimum PVIN for start-up VS Inductance
L(uH) PVIN min（mV）
0.47 100
1 90
1.5 80
2.2 80
3.3 80
4.7 80
6.8 110
22 Fail to start up
Note: The inductance DCR selected in the experiments is controlled within 40 mΩ, and the experimental influence caused by the difference in Rdc is reduced as much as possible.

As is shown in Table 3-4, when inductance is smaller than 4.7 uH, with the increasing of inductance, the TPS61299 can achieve lower PVIN start up. However, when inductance is higher than 4.7 uH, continuing to increase inductance does not achieve a lower PVIN startup as expected. The reason why Startup fails to output normally should be related to the total energy of the inductor during excitation and discharge, so the reasons for this is further analyzed in Section 3.4.1.