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PMP10651: Question Regarding the Schematic

TI-CSC
Genius 14860 points
Part Number: PMP10651


Tool/software:

Hello E2E Experts, 

God day.

I wanted to mention the extra bypass capacitor in the red circled part. Is the load capacity of a linear regulator that small? Also, can I understand that there must be feedback after the bead as meaning that the bead must be added exactly at the location of the blue arrow?

Regards,

TI-CSC

  • 0
    TI__Intellectual 900 points

    Hi,

    for the TPS7A470X LDO, it needs minimum 10uf as cout to ensure stability. more Cout is needed if you need a better transient response on that voltage rail.

    I have drawn out the LMZ1701 with a 2nd stage filter. Please see attached.

  • 0 in reply to Sarmad Abedin
    TI__Genius 14860 points

    Hello Samad,

    Good day.

    The IC that must be ultimately supplied requires a very large capacity (1000uF). However, buck converters such as LMZ have limited output capacitor capacity. (Also stated in the datasheet) This buck converter is also supported by WEBENCH, so setting the output voltage or obtaining the output capacitor is easy to use in a typical environment. However, I asked about the possibility of LDO enabling it to meet the conditions I want (1000uF) -- si this possible?

    000uF is too harsh, so at least 470uF is fine. This means that large LDO output capacitors can interfere with or ruin the operation of the step-down cone.

    Regards,

    TI-CSC

  • 0 in reply to TI-CSC
    TI__Intellectual 900 points

    Hey CSC,

    The limitation of the Cout on this buck module is not because of the topology but because it has internal compensation that is chosen to provide stability over a certain bandwidth of the converter. 1000uf is commonly seen on buck supplies especially at smaller Vout. I would recommend you go with more of a discrete solution and work with converters/controllers that provide external compensation.

    thanks.