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

3.3 The Way Vout Influence Start-up Process

This paragraph focuses on effects of Vout regarding with the lowest PVIN start-up. The Table 3-3 shows minimum PVIN supporting for regular start-up , under the condition that AVIN =0.7 V , L=1 uH the same, and target VOUT varies from each other.

Table 3-3 Minimum Start-up PVIN for Different VOUT
VOUT (V) PVIN min( mV)
1.8 90
3.3 120
5 140

As is shown inTable 3-3, the larger the VOUT is , the lower the PVIN startup can be achieved. The inductor current with different VOUT is shown in Figure 3-5. When VOUT is larger than AVIN, the device works under Boost mode. With PVIN no much difference, the main difference lie in the period when high side PMOS turns on, denoted as Toff.

As is shown, the lower Vout is , the more flat the inductor current ramp down, the longer Toff time is, which means more energy is converted to the output side during one switching cycle, because using the Toff period:

Equation 3. L d i d t = V O U T - P V I N

Thus the power converted to the output bus can be sorted from largest to smallest : VOUT=1.8V, VOUT=3.3V, VOUT=5V.

In conclusion, lower VOUT can achieve better and faster start up behavior.

GUID-20230822-SS0I-PTRH-CTJ5-VVVQ73FNHHFF-low.svg Figure 3-5 Inductor Current for Different VOUT