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TPS55288EVM-045: TPS55288EVM-045 Issue After Output Enable

Part Number: TPS55288EVM-045
Other Parts Discussed in Thread: TPS55288

We are using the TPS55288 on a new prototype, with an input voltage of 3.6V and a target output voltage of 5.5V. We discovered an issue during bring up so we purchased the TPS55288EVM-045 to rule out the possibility of layout issues. Unfortunately, we have experienced the same issue whilst using the TPS55288EVM-045. After the output enable bit is set in register 0x06, the input voltage drops rapidly to below the VVin_UVLO threshold and the output voltage increases at a faster rate than the slew rate setting. This is shown in the scope trace below (red trace is the input voltage, blue trace is the output voltage). After this has occurred, reading the registers gives the default values (including the output enable bit being set back to zero). 

  • Hi Emma,

    When OE bit is set, the device will start up and after about 3.4ms, it will get into the target output value.

    Which slew rate do you mean here? If you mean 03h register, the value is the output change rate, not the startup rate.

    I am guessing if the input wire is long and you startup with loading, so the current through the wire will cause the  voltage drop.

    Regards,

    Bryce

  • Hi Bryce,

    The same effect on the input voltage is seen even with no load applied at the output. 

  • Hi Emma,

    Can you also probe the inductor current, SW1 and SW2 waveforms on one page?

  • Hi Bryce,

    I have the below trace with: Red: Input, Blue: Output, Green: SW1, Yellow: SW2.

    (Please let me know if there is a better way of sharing scope data on this forum than as images)

  • Hi Emma,

    Thanks for feedback, I will also test on bench to check Vin waveforms drop.

    You can also share the image, file, data and link about the data.

    Regards,

    Bryce

  • Hi Emma,

    Below is my bench test waveform, I used the same working condition as yours. Input voltage of 3.6V and a target output voltage of 5.5V, write to OE bit to startup with no load. But I don't find the Vin drop as yours, can you also probe the inductor current to see if there is large inductor current during the startup?

    CH1-Vin, CH2-SW1, CH3-SW2, CH4-iL

    Regards,

    Bryce

  • Hi Emma,

    We have not seen an update from you for three weeks, so I assume the questions are answered and the issue is solved.
    I close this thread now. If there is still something open, please reply and the thread will get opened again.
    If you have any other question or of the thread has been locked, please open a new one.


    Best regards,
    Bryce