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TPS7A54: Bias supply

Kazuki Itoh
Genius 10660 points
Part Number: TPS7A54

Hi team,

My customer is considering TPS7A54 to generate 2.3V/15A from 2.5V rail by current sharing configuration.

The available rail is limited, so I think they will go without BIAS.

Just for reference, if BIAS is used, is clean power supply needed?

Or, the noise at the BIAS pin doesn't affect the noise performance?

Regards,

Itoh

  • 0
    TI__Expert 6955 points

    Hi Itoh-san,

    I am assuming that you mean you will be having a 1.5A rail from the 2.5V->2.3V is that correct? if so I don't see a problem without using the Bias rail. If you do decide to use the Bias rail the PSRR is pretty high from Vbias to Vout see graph below, so you will have a reduction of ~70dB across frequency for the noise that is on Vbias. If you do use the bias pin you will also have to connect a local 10uF capacitor from bias to GND to help with transients and this capacitor will also help alleviate noise as well.

    Regards,

    Mark

  • 0 in reply to Mark Sellers
    TI__Genius 10660 points

    Hi Mark-san,

    No, I mean I want to power 2.5V->2.3V 15A rail with 4x TPS7A54 with current sharing configuration.

    Regards,

    Itoh

  • +1 in reply to Kazuki Itoh
    TI__Expert 6955 points

    Hi Itoh-san,

    My fault i missed the current sharing part of the first question. Yes you can achieve this through current sharing. You will need to use ballast resistors or amplifiers though. There is a good app note below on how to use ballast resistors with parts that are in the same family of LDOs as the TPS7A54's. 

    A couple of lessons learned here after doing this a few times I would error on the side of using 5x LDOs here as the current sharing is not always perfect and while it is possible to use 4, you will get better results out of the ones using 5 LDOs. The other reason i recommend using 5 LDOs is then each one will only be expected to run 3A, which will effectively lower the dropout voltage and allow you to get higher PSRR and better transient performance out of them. Using 5 will allow you to lower the dropout voltage to around 120-130mV when using 3A, which also gives you a little bit of room to have tolerance on your input rail.

    Hope this helps clear up some questions now!

    Regards,

    Mark

    https://www.ti.com/tool/TIDA-01232