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TM4C129ENCPDT: why Capacitor across power connector

Nishitha Chandrasekar
Intellectual 700 points
Part Number: TM4C129ENCPDT

Hi Sir,

I have a doubt, I have verified lot of control card, LED  module,  each control card and LED modules have a power connector as 5V from power supply, they have capacitor across power connector, may i know why capacitor is used their and how to calculate the capacitor value. I dont know this. please help me. In my LED module they have used 10uf with 6V rating. I dont know how they calculated this value 

  • 0
    TI__Guru*** 135355 points
    If by across the power connector you mean a capacitor between 5V and GND, then the answer is that is a filter cap to handle the ripple from the power supply and reduce noise in the system. The capacitor value is generally calculated based on the expected ripple voltage on the input and the tolerated ripple of the output. 10uF is pretty commonly used as it has a good trade-off between effectiveness of reducing the ripple voltage and size taken up on the PCB, making it useful for generalized applications where there will be variance in the input ripple voltage.
  • 0 in reply to Ralph Jacobi
    Intellectual 700 points

    Dear Sir,

    I can understand your answer, still i have some more questions, can you pls explain with some example.

    Currently i am using 5V 40Amps SMPS, its AC signal has 220V, 2.5Amps , 50hz frequency means how to know the input ripple voltage of this SMPS and place the correct capacitor across power connector??

    I have tried this formula whether it is correct???

    Ripple factor  = 1/4x1.732xfxCxRL

    RL = 5/40A = 0.125Ohms

    C= 470uF/25V

    Then ripple factor value = 0.49% this is correct orelse

    if i used 10uf instead of 470uF  then ripple factor value = 0.43% this is correct???

    Kindly help me

  • 0 in reply to Nishitha Chandrasekar
    TI__Guru 71526 points

    Hello Nishitha, 

    Thank you for using E2E, and in an effort to more fully understand your concern, can you tell me more about your design, please?  Can you post the schematic?  What TI devices does it use? 

    We have many SMPS Reference Designs, such as: www.ti.com/tool/TIDA-01495 .  And we also use WEBENCH for power supply design, which takes into account not only the ripple effects, but the overall power supply performance.  You could give this a try for your design: https://webench.ti.com/power-designer/switching-regulator?powerSupply=1  .

    Regards,

    ~Leonard