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TPS62420: Layout question about feed-back.

Denis Alain1
Intellectual 600 points
Part Number: TPS62420


Hi,

We are doing an ECO and all DC-DCs have been re-layouted. All high-current parts are on TOP and the feedback resistors are on bottom. We connected the feedback resistor directly with VIAs in pad on output capacitors without small traces.

1) Is-it OK? Or we need to have feedback resistors connected to a less noisy area? I know that LC area have high freq current. I am not sure if it can affect the feedback.

Inside the following picture:

RED = TOP

BLUE= BOTTOM

Yellow rectangle: Vias in PAD to connect the feedback resistors.

2) Same questions for the feedback pin (pin 4) of the 1st DC-DC.

3) I am not sure why this DC-DC has a separate feedback pin (pin 4) vs resistor divider pin (pin 5). I never saw this on others DC-DCs. Can you explain me purpose of this feedback pin vs voltage divider?

Thanks,

Denis Alain, Eng

  • 0
    TI__Mastermind 26500 points

    Hi Denis,

    I will provide a feedback later today.

    Regards,

    Febin

  • +1 in reply to Febin
    TI__Mastermind 26500 points

    Hi Denis,

    I would like to share an App note that provides some Layout guidelines for a buck converter.

    https://www.ti.com/lit/an/slyt614/slyt614.pdf

    Regarding the IC pins, the internal design and pin-out for buck converters can be different from device to device. For TPS62420, the pin description is clearly explained in the datasheet. FB1 pin is a voltage sense pin which provides a direct connection from Vout to the error amplifier and ensures a better load regulation and faster transient response.

    I would like to understand if there is a possibility to change to newer devices during this ECO. TPS62420 is a pretty old part and I do not recommend this in newer designs.

    Regards,

    Febin

  • 0 in reply to Febin
    Intellectual 600 points

    Hi Febin,

    It is not too late to change the DC-DC. Do you have a suggestions with similar features and packages? The main issue is the lead time. It is a nightmare right now.

    Thanks,

    Denis Alain, Eng

  • 0 in reply to Denis Alain1
    TI__Mastermind 26500 points

    Hi Denis,

    Please have a look at our latest dual converter which is not yet RTM but can be used for prototype builds.

    https://www.ti.com/lit/ds/symlink/tps62442-q1.pdf

    Regarding the LT, honestly I would like to be transparent here and not give you false hopes. It is quite a challenging situation worldwide and we need to simply wait for some more time until the market cools down. I cannot assure any LT for this device. However, when do you need the samples and what quantity?

    Regards,

    Febin

  • 0 in reply to Febin
    Intellectual 600 points

    Hi Febin,

    Thanks for the information. Since we have orders already inside the pipeline for the original DC-DC, I will keep it on the current design. Our goal is to change only the FPGA since it is not available anymore. We will do another ECO later to upgrade other parts, but we will need to place orders at the right moment to have stocks when the new version of the PCB will ramp-up. I will keep your suggestion for this next ECO.

    Best Regards,
    Denis Alain, Eng