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UCC28781: Audible noise in ABM

Marc Fournier
Prodigy 10 points
Part Number: UCC28781

Tool/software:

Hi,

The audible noise is really high when the converter is in ABM (burst mode). In AAM, there is no noise.

I tried to adjust Rbur1 and Rbur2, to exit burst mode at 20% of max power. But actually it exits this mode more at about 80% of full power.

In the excel file (SLURAZ0), what does the line "target to enter ABM" means ? It is not clear as I am more interested to exit it quickly considering the noise.

I would expect a percentage to exit ABM, not to enter in this mode.

Can you provide advices to lower the noise or at least to lower the burst mode range ?

Best regards,

Marc

  • 0
    TI__Mastermind 24375 points

    Hi Marc,

    Thank you for reaching out.

    The target to enter ABM is nothing but when the converter is operating at full load in AAM mode as the load is reduced at what percent of full load, the converter enters into ABM. This is ideally set at 40-50%. The exit of ABM will happen at very low load where the converter enters Standby and low power modes.

    Regards,

    Harish

  • 0 in reply to Harish Ramakrishnan5
    Prodigy 10 points

    Thank you Harish,

    I have one more question:

    - Is it possible to lower the negative current used to achieve ZVS ? In my simulation, I needed a lower negative secondary current (-3.75A) than in reality (-4.6A). Consequently, the losses are higher than expected even though the real Coss is lower than in simulation. I understand that this current is tuned automatically to achieve ZVS on the primary FET, but I want to be sure.

    Thanks,

    Marc

  • 0 in reply to Marc Fournier
    TI__Mastermind 24375 points

    Hi Marc,

    I think this might be difficult to achieve as most of this is internal. Ultimately this has to be as you pointed out optimizing for Coss of primary and SR FET along with the clamp capacitance. Below are some tradeoff based on study considered:

    Regards,

    Harish