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TPS548D21: TPS548D21 unity Gain BW

Ramya Gorantla
Prodigy 170 points
Part Number: TPS548D21

HI,

We are using TPS548D21 as 1V core supply to the Ethernet Switch.

We have AVS (Adaptive voltage scaling)  feature in ethernet switch for 1V core supply.                                        

As per the switch design guide: The AVS is suitable to work with external voltage regulators which have a unity gain bandwidth in the range of 15–300 KHz.

 

I am not able to find the Unity gain bandwidth of the regulator in the datasheet or in any of the webench graphs.

 Can you please let us know the unity gain BW for the regulator and also share the bode plot information available for this regulator.

Regards,

Ramya

  • 0
    TI__Expert 7500 points

    Hi Ramya,

    Our US team is on holiday. They will respond to you soon.

    Thanks,

    Lishuang

  • 0
    TI__Expert 5310 points

    Hi Ramya,

    The TPS548D21 uses a DCAP3 control topology, which is difficult to model with Webench in the frequency domain given that it uses adaptive on-time control. The unity gain bandwidth will depend particularly on the RAMP setting, output capacitance, and inductance in your particular design. As far as ensuring stability goes, I would follow the recommendations in section 8.2.3.4.1 and table 7 in the datasheet regarding output capacitance and ramp selection. Also, installing a 10ohm resistor between TP6 and TP7 using the EVM will allow you to conduct a bode plot measurement on the EVM. I can provide guidance on measuring the frequency domain stability on the customer's design if needed as well.

    Regards,

    Alec Biesterfeld

  • 0 in reply to Alec Biesterfeld
    Prodigy 170 points

    Hi Alec,

    Thanks for the Reply..

    Can you help in getting the unity gain band width for my design

    This is the configuration which we are using for our design:

    VIN =12V

    Vout=1V

    ILOAD Max= 25Amps

    ILOAD min = 5 Amps

    Switching frequency = 650 KHz

    Inductor =440nH ( IFLR5151HZERR44M01)

    COUT total = 6X 330uF ( Tantalum Caps) , 3X100uF (ceramic)

    Please let me know if any other information required.

    Please note that our switch requirement for using this regulator is as follows: The AVS is suitable to work with external voltage regulators which have a unity gain bandwidth in the range of 15–300 KHz”. 

    Regards,

    Ramya

  • 0 in reply to Ramya Gorantla
    TI__Expert 5310 points

    Hi Ramya,

    In general, the Unity Gain Bandwidth can be estimated using the following formula:

    In this estimation, g_m is an internal gain/transconductance, tau is the ramp time constant ( assuming you are using the recommended 13.5 us). I ran the calculation using the details in your application, and I would estimate the unity gain bandwidth of your design to fall between 110 kHz and 200 kHz depending on the derating of the output caps. I would verify with a frequency analyzer if possible given the requirements of the unity gain bandwidth, but my estimation appears to satisfy your requirement.

    Regards, 

    Alec Biesterfeld