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TPS61029 Start-Up Issue

Shane Murphy
Prodigy 65 points
Other Parts Discussed in Thread: TPL5111, TPS61029, TPS61020

We are attempting to power a device using the TPS61029 boost converter.  I have been using the evaluation kit for the TPL5111 which has the TPS61029 to power this new component on the bench and I am having issues.  Sometimes the TPS61029 is able to power up properly but other times it has issues which can be seen in the attached scope plot.  The output voltage(blue waveform) is supposed to be 3.3V but as you can see in the plot it doesn’t stay at 3.3V, it drops down to 2V.  During these failed startup attempts it will eventually settle at a 2V output.  The yellow waveform is the output current(100mV = 100mA) and the input voltage to the regulator is 3V.

What could be causing this behavior?

  • 0
    TI__Mastermind 46905 points
    The TPS61029 has small current limit when VOUT is lower than VIN, please refer to the application report"TPS61020 Boost Converter Start-Up and Precharge". i think it is the reason the TPS61029 stay at VOUT=2V

    if carefully check the output current waveform, it seem there is very high spike in the yellow line which may cause the TPS61029 trigger current limit. so the VOUT of the TPS61029 drop down below VIN and the TPS61029 restart.
  • 0 in reply to Jasper Li
    Prodigy 65 points

    Thank you for the application note, we may need to switch in the load after the power supply is stable.  This could address the failures where the supply never starts properly.

    Most of the failures however seem to occur after the power supply "starts up".  As you can see in the attached plot, the output voltage reaches 3.3V and stays there for 700+ms(the purple trace is the input voltage to the supply).  There is then a current spike as you mentioned which causes it to drop to 2V.  My question is why doesn't it recover?  The current draw drops to below 200mA.  Shouldn't the supply be able to recover from this state? 

  • 0 in reply to Shane Murphy
    TI__Mastermind 46905 points
    if VOUT drop below the VIN, the device will trigger its internal short circuit protection logic and try to restart again (pre-charge then start to switch). and the device could be stay at pre-charge stage if the load is high.
    the solution should be avoiding the VOUT falling below the VIN. could you check the current spike value when the VOUT drop from 3.3V to 2V?
  • 0 in reply to Jasper Li
    Prodigy 65 points
    The current spike when Vout drops from 3.3 to 2V is in the 1.2-1.5A range.

    How long should the device stay in pre-charge if the load isn't high though? As you can see from the yellow trace the current sits below 200mA for hundreds of milliseconds without the output voltage recovering.
  • 0 in reply to Shane Murphy
    TI__Mastermind 46905 points
    the pre-change exits only VOUT is charged to near VIN. the VIN=3, VOUT=2 in the condition, so the device will never switching.
  • 0 in reply to Jasper Li
    Prodigy 65 points
    Why isn't Vout increasing though? The output current is less than 200mA, the current limit during pre-charge should be much higher than this correct? Yet the output is stuck at 2V with a low output current.
  • 0 in reply to Shane Murphy
    TI__Mastermind 46905 points
    please have a look at the datasheet page 11. the pre-change current at VIN=3, VOUT=2V is not higher than 150mA.