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LM53603-Q1: Output Voltage

Part Number: LM53603-Q1
Other Parts Discussed in Thread: LM53603

Hi,

The datasheet have following comments;

"Under no conditions should the output voltage be allowed to fall below zero volts."

Is this comment(falling below zero volts) how condition is supposed?

Best Regards,

Kuramochi

  • Kuramochi-san,

    The output voltage can go negative in cases where there is an inductive load and the output becomes shorted. This may happen in a USB charging application because the short circuit can occur at the end of the cable, and the inductance of the cable can pull the output negative. The main issue with the output going negative is that the BIAS pin is usually connected too the outut. A negative voltage on the BIAS pin will cause the IC to malfunction. Protection of the BIAS can be implemented by using a RBIAS and CBIAS and Schottky diode in parallel with CBIAS.

    Perry
  • Hi Perry-san,

    Thank you for your answer.

    I have an additional question.
    The LM53603 seems to delay the rising time of Vout when VIN drops below UVLO voltage and rises above UVLO voltage.
    What is occurring this delay depend on?
    Is it Vout setting value only? or is it related to Vin rising time, load current, and so on?

    Best Regards,
    Kuramochi

  • Hello Kuramochi-san,

    I am Robert Blattner and work with Perry-san. Once input voltage rises above input UVLO level, soft start begins after a ~700 us delay. During soft start, the output voltage set point rises from 0 V to nominal voltage over ~2 ms. This ramp does not depend on load. Also, during this period reverse current does not flow so output is not pulled down, making soft start safe if the output has voltage before start up. Is this the delay that you are observing?

    Regards, Robert
  • Hi Robert-san,

    Thank you for your reply.

    Sorry for the lack of explanation.
    I'm hearing that this delay is caused by setting Vout to over 6V.
    However I don't know the principle of this delay.

    So I would like to know what this delay is depended on.


    I send you the waveform by e-mail if you need.

    Best Regards,
    Kuramochi

  • Hello Kuramochi-san,

    Yes... Please send waveforms to robert.blattner@ti.com.

    Regards, Robert
  • Robert-san,

    I send you a material by e-mail.
    Could you confirm it?

    Best Regards,
    Kuramochi
  • Hello Kuramochi-san,

    I have recieved your information and am trying to reproduce the effect that you show in our lab.

    Regards, Robert