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TPS7H1111-SEP: ferrite beads does not affect Vout regulation stability?

Kazuhiko Hirano
Genius 15088 points
Part Number: TPS7H1111-SEP
Other Parts Discussed in Thread: TPS7H1111-SP, DAC39RF10-SP

Tool/software:

Hello,

Looking at DAC39RF10-SP/SEP datasheet Figure 8-22 and 8-23, ferrite beads are used at TPS7H1111-SP Vout. Those ferrite beads does not affect Vout regulation stability at all?
Are there anything to be cared about using ferrite beads?

Best regards,

K.Hirano

  • 0
    TI__Genius 12100 points

    Hi,

    It is acceptable to use ferrite beads downstream from the TPS7H1111 output. If using a ferrite bead, the OUTS connection should be placed before the ferrite bead to keep the ferrite bead outside of the control loop. 

    Thanks,

    Sarah

  • 0 in reply to Sarah Koch
    TI__Genius 15088 points

    Sarah,

    Thank you for your response.
    As a rule of thumb, to keep the ferrite bead outside of the control loop, how much distance should be keep between Cout and the ferrite bead?

    Best regards,

    K.Hirano

  • +1 in reply to Kazuhiko Hirano
    TI__Genius 12100 points

    Hi Hirano-san,

    The bulk tantalum COUT should be placed inside the control loop near the LDO output pins. As far as I am aware, there is no strict requirement on how close the ferrite bead can be placed to the LDO output. The important thing is to ensure that the OUTS connection occurs before the ferrite bead. Generally ferrite beads are placed closer to the load, so this would naturally create some separation from the LDO output.

    The datasheet does have some additional guidance and data comparing performance of the TPS7H1111 with and without a ferrite bead. I believe these tests were done on the EVM if you would like to see a reference board layout. 

    Thanks,

    Sarah