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TPS55330 with dynamic load

Leonid Gnusin
Prodigy 150 points
Other Parts Discussed in Thread: TPS55330

We design boost converter based on TPS55330, with 4.2V input and 5-10V output for our 125KHz RFID application. During evaluation found that output voltage drop is too high ~ 400mV @5V output, with dynamic load of 200-300mA peak @125KHz. Was tested also TPS55330 EVB and found the similar behavior. Can you please explain how to improve the design to reduce output voltage drop? See attached pdf of measured output voltage and current waveforms.

TPS55330 dynamic load_EVB.pdf

  • 0
    TI__Mastermind 35165 points

    Hi Leonid,

    The transient response of a non synchronous converter from no load to load can be slow. Therefore the drop in the output is most likely caused by the transition from no load to the dynamic load. In steady state with the dynamic load I expect the output will remain stable.Operating with VIN closer to VOUT can also make this worse because the IC is usually pulse skipping.

    The transient response can be improved by increasing the output capacitance and then selecting new compensation. The new compensation should be selected at full load.

    Best Regards,
    Anthony

  • 0 in reply to Anthony F
    Prodigy 130 points

    We have been using the TPS55330 to take 3.7V to 18V (400mA).  During steady state testing with an electronic load, it performed well but we were getting huge drops (several volts) in the application when we go from near zero output load to 400mA.  Speeding up the control loop didn't do much for us.  The only way to substantially improve the droop was to use a LOT of output capacitance (more than we can fit on the PCB).  The TI eval board shows the same slow response to step loads.  We came across this post while looking to see if anyone else had a similar problem with this part.  Just a FYI for anyone else considering the TPS55330 for applications with large step loads or transitions that go from low load (pulse skip mode) to a high current.  

  • 0 in reply to mtucker
    Prodigy 150 points

    We adopted a council to increase capacity and update compensation (this is important!), which has brought us tangible improvements. We also increased the switching frequency and increased the power inductor. We hed to redisign the PCB to solve it. In the final, we got acceptable results.