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TAS5805M: efficiency

Ella Zhang
Prodigy 330 points
Part Number: TAS5805M
Other Parts Discussed in Thread: TAS5805

Dear all

We found that the efficiency of TAS5805 increased with the Fsw. How can we explain this phenomenon?

We have tested the efficiency of TAS5805EVM in the following condition:

1.  Remove the beads and capacitor;

2. PVDD=15.4V;Load=6ohm;Output power=10W;

The test result is：

Fsw=384kHz；IIN=2.222A

Fsw=480kHz；IIN=2.157A

Fsw=576kHz；IIN=2.123A

Fsw=768kHz；IIN=2.073A

Thanks and best regards,

Ella

  • 0
    TI__Mastermind 24835 points

    Hi Ella,

    So you are using inductors in the output filter, right?

    The ripple current is lower with higher Fsw.

    Best regards,

    Shawn Zheng

  • 0 in reply to Shawn Zheng
    TI__Prodigy 330 points
    Hi Shawn，

    The above experimental results is tested without LC filter and beads in TAS5805EVM.

    When I use LC filter, the efficiency decrease with switching frequency.
    But when I use bead or without bead, the efficiency increase with frequency.

    Thanks and best regard.
    Ella.
  • 0
    TI__Genius 9995 points

    Hi Ella,

    As to efficiency of TAS5805's FB application, some main points are needed to be taken into consideration:

    • Output power is less than 2*10W in most TAS5805 FB application. Usually, efficiency is one of the main consideration;
    • When it comes to FB application, EMC performance are the main concern. Hence, only BD mode with SS are highly recommended.

    Further, usually, PVDD of TAS5805 is powered by customer's power board or an adapter, which usually shows a PI filter. Switching frequence of TAS5805 usually needed to be chosen according to cut-off frequency of the PI filter to obtain a good EMC performance.

    Based on the facts above, in TAS5805's FB applicaton, Fsw=384KHz is usually recommended for customer. But, it may be needed to adjust according to customer's applcication.

    Finlly, referring to https://e2e.ti.com/support/audio/f/6/p/735999/2718882?tisearch=e2e-sitesearch&keymatch=%20user:320278#2718882 , efficiency is affected by:

    1. Rds(on)
    2. Switching loss
    3. X value of FB

    When you increase your switching frequency, the swithcing loss increses and FB has bigger HF resistance. Hence, efficiency should be worse.

    Your results are not reasonble based on the analysis above, this is mainly due to the duty signal works on dummy load. Please use a speaker to test again.

    Regards,

    Alix Wan.