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TLV62130A: Addition of extra LC filter, stability concerns

Alexander De Geeter1
Prodigy 115 points

Part Number: TLV62130A

Tool/software:

Hello,

For a new design i would like to power the transceivers of a FPGA with a buck converter.

Quite a while ago i have seen your presentation of low noise buck converter design: Low-noise and low-ripple techniques for a supply without an LDO PPT

So i would like to implement the solution with an extra LC filter with a bead, we would like to use the TLV62130A for that.

One problem is that the cuttof frequency of the LC filter has to be larger the loop bandwidth to have this double pole not affect the stability.

However with DCS control it is hard to estimate and control the loop bandwidth due the non lineair behavior, therefore we would to change the setup a bit.

If we connect the Vos pin to the output of the converter, then the fast non lineair loop isn`t so much impacted by the extra bead filter.

As far as i know is the upper voltage error amplifier quite slow, so we can connect this pin after the bead filter to regulate the DC drop away.

But we wanted to double check if we don`t forget anything and wanted to have your opinion. 

We know you have some dedicated buck converters available for this, these inject the inverse of the bead filter response as far as i know.

But these aren`t available in our basket.

Kind Regards

Alexander

  • 0
    TI__Genius 15110 points

    Hello Alexander,

    Trying to understand your requirement and please confirm below:

    As of now TLV62130A VOS pin is connected to output filter capacitor and in your case you wanted to use extra ferrite bead which will be connected after the output filter cap and you want to connect VOS pin after the ferrite bead ? Also you want to connect feedback pin after ferrite bead via resistor divider or even with ferrite bead you want to connect feedback pin from output filter capacitor via resistor divider?  

    Regards,

    Haseen.

  • 0 in reply to Haseen Reddy Siripi Reddy
    Prodigy 115 points

    Hello,

    No the plan is to connect the inner fast COT loop direct at the capacitor (Vos pin) and the slow voltage loop after the bead.

    In the past we measured the loop response of this outer voltage loop and this seems to be quite slow (a couple of 100Hz), so we don`t expect that the high bead filter will affect this loop response and the total stability of the converter.

  • 0 in reply to Alexander De Geeter1
    TI__Genius 15110 points

    Hello Alexander,

    From the above it is seen that its a deviation from our recommended connection for FB pin.

    We have not validated internally with this configuration and we would like you to test thoroughly and take the decision.

    Regards,

    Haseen.