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UCC27517 output current

K.Hamamoto
Guru 12155 points

Hi

I have some question about output current(sink/source).

On the datasheet, it is defined as following.

On the other hand, the drive output current is a pulse current at some frequency.

For example, the RMS current is 318mA when Ipeak is 900mA and frequency is 7MHz.

If RMS current can be assumed as continuous current,  it exceed the above spec. Is that correct?

Regards,

Koji Hamamoto

  • 0
    TI__Mastermind 31580 points
    Hi Koji-san,

    I have asked one of the HPDS applications engineers to respond to your post.

    Thanks

    Peter
  • 0
    TI__Mastermind 23015 points

    Hello Koji,

    The best method to determine the average current from the gate drive power dissipation is to examine the total gate charge of the MOSFET and the operating frequency.

    The gate drive power is determined by Pg=Qg * Vdd * fsw. The current will be Ig=Qg * fsw. The average current of charging the MOSFET for turn on has to be discharged by the turn off (or sink).

    For the frequency you mention of 7Hz the maximum gate charge to stay within the 0.3A average current rating will be: Qg=Ig/fsw =0.3A/7MHz=42.8nC.

    At these higher operating frequencies, be sure to confirm the power dissipation, including the gate drive current, as above, plus the quiescent operating current at the operating Vdd.

  • 0 in reply to Richard Herring
    Guru 12155 points
    Hi Richard-san

    Thank you for your support.

    I understand that the output current can be estimated by the above calculations.
    On the other hands, how can we estimate the output current if the output is a transformer (not MOSFET. It drives trans)?

    That drive current is ; peak = 0.9A , frequency = 7MHz.

    Regards,
    Koji Hamamoto
  • 0 in reply to K.Hamamoto
    TI__Mastermind 23015 points

    Hello Koji,

    Thank you for the clarification that the driver load is a transformer, so that could be a different calculation assuming the transformer is not driving a MOSFET on the secondary side.

    In the earlier post, you had mentioned a peak current of 900mA and RMS of 318mA. Can you provide the details of the waveform shape and maximum duty cycle? Can you confirm what type of load is on the transformer output, resistive capacitive etc.

  • 0 in reply to Richard Herring
    Guru 12155 points
    Hi Richard,

    Thank you for your quick support.

    Can we talk on e-mail?
    Because I have some waveform however that is confidential.

    Regards,
    Koji Hamamoto
  • 0 in reply to K.Hamamoto
    Guru 12155 points
    Hi Richards,

    Can we talk by e-mail about this post?
    I can send the schematic and waveform.

    Regards,
    Koji Hamamoto
  • 0 in reply to K.Hamamoto
    TI__Mastermind 23015 points

    Hello Koji,

    I looked for your email, but you are not on our mailing lists. My email is richard_herring@ti.com .