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TPS543620EVM: Question about Enable and Adjustable UVLO

Jayden Qiu
Intellectual 1125 points
Part Number: TPS543620EVM

Hi team,

I'm Jayden, I have some questions about enable and adjustable UVLO when I run the EVM in the lab.

The waveform on the left shows EN is float without RENT and RENB. Only the pullup current Ip sets the default state of the pin to enable. The  waveform on the right shows EN with RENT and RENB. The pullup current Ip and Ih sets the state of the pin to enable.

1.Why there is a 1.18V voltage platform in EN when it is floated at start-up sequence?

2. Why there is a voltage slope change in BP5?

3. SW has a single pulse before Vout is established. It also occurs in datasheet Fig8-10. Why does this single pulse appear?

Thanks. Look forward to your reply.

Question about TPS543620.pptx

  • +1
    TI__Mastermind 18370 points

    Hi Jayden,

    1)  This is not a plateau, but a low grade slope.
         Before the device is powered up, En is pulled up by 1.5 uA, which may not be enough to pull EN all the way up.
         As soon as the EN voltage riches above 1.3V, the EN is pulled up by 11.6 uA and the slope will be faster, pulling EN all
         the way up.

    2) The change in BP5 ramp is due to the internal circuitry and is expected. Nothing to be concerned about.

    3)  The SW pulses at the beginning of Vout ramp are narrower and less frequent (DCM).
          When SW is captured using a sampling/digital oscilloscope, some of these pulses may not be sampled and will not
          register. This is just a sampling oscilloscope artifact.

          Also if DCM is enabled, you may be in DCM mode with less frequent pulses.
          I don't think there is always one pulse showing up before other pulses. But just less pulses and even less 
          sampled/registered pulses in the beginning of ramp up.

    Hope this makes sense.

    Regards,

    Yitzhak Bolurian

  • 0 in reply to Yitzhak Bolurian
    TI__Intellectual 1125 points

    Hi Yitzhak,

    It resolve my issues. Thanks.

    BRs

    Jayden