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LM5163-Q1: LM5163 about CIN cap choose

Lawrence He
Genius 3280 points
Part Number: LM5163-Q1
Other Parts Discussed in Thread: LM5164-Q1, LM5163

Dear,

our client was use LM5163-Q1, also we fill up excel file as attached, than we find some question as below:

1. we saw the LM5164-Q1 EVM , C8=33uF, But we use excel tool CIN CAP value only need >2.2uF

so LM5164-Q1 EVM parallel CIN cap  C8 & C9 & C10 was must need?


2. about CIN Datasheet 8.2.2.5

if the LM5163-Q1 is not located within approximately 5 cm from the input voltage source.

it is mean over 5cm, suggestion CIN more higher 2.2uf right?

3. about Datasheet 9. Power Supply Recommendations
avoid VIN each time the input supply is cycled ON and OFF. The parasitic resistance causes the input voltage to dip during a load transient. If the converter is operating close to the minimum input voltage, this dip can cause false UVLO fault triggering and a system reset.

so it is add CIN reason? if we do not need UVLO function , could we can remove CIN cap?

if any suggestion, Please advise me.

Thanks,

Best regards,

Lawrence.

  • 0
    TI__Expert 4720 points

    Hi Lawrence,

    2. it is mean over 5cm, suggestion CIN more higher 2.2uf right? Yes.

    3. That is part of the reason. the input parasitic inductance may cause loop unstable. 

    Please refer to these articles for more details:

    http://www.ti.com/lit/an/snva538/snva538.pdf

    http://www.ti.com/lit/an/slua929a/slua929a.pdf

  • 0 in reply to Neal Zhang
    Genius 3280 points

    Hi, Neal


    Thank you for your reply.


    about question one


    our application is automotive  and input form Battery to LM5163, and our client concern CIN capacitance.

    we use Excel tool as attached and our setting, we find optional EMI filter damping capacitance is 10uF

    https://e2e.ti.com/cfs-file/__key/communityserver-discussions-components-files/196/LM5163_2C00_-LM5164-Quickstart-Calculator-rev3_5F00_316K_5F00_100K.7z

    and LM5146EVM damping capacitance is 33uF.

    how to chooce CIN capacitance, was follow Excel tool?

    4.7uf // 10uf // 2.2uf  or  only 2.2uF is good enough

    ----------------------------------------------------------------------------------------------------------------------------------------------------------------

    By the way we use long cable 150cm connect to LM5146EVM, and remove C8(33uF) , and we find Vout 5V was stable....
    so we really confuse, should we can remove C8  capacitance in our design.

    If any suggestion, Please advise me.

    Thanks,

    Best regards,

    Lawrence.

     

  • 0 in reply to Lawrence He
    TI__Expert 4720 points

    Hi Lawrence,

    It's suggested to use 10uF cap in parallel with the 2.2uF cap, in order to prevent loop stability problems.

    Do you need to pass EMI? The attached calculation tool you attached is for conducted EMI, and 4.7uF/2.2uH is EMI filter.