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+24V input ，use TPS54331, power down maintain the board work 300ms

user4973896
Expert 1555 points
Other Parts Discussed in Thread: TPS54331

my board power dissipation is 5W to 10W when it normally works，Now input power is +24V ，I use TPS54331 to convert +24V to other power to make the board work，if i want my board still  work  300ms  after  power down the 24V , what  a  captiance should  i  add  between the +24V and  gnd , how to choose?please  help  me   ! 

  • 0
    TI__Expert 5745 points

    The energy in the Cap is E=C*V*V/2. And the energy E in the input cap should be Dissipation/Efficiency. But you still need to do the test to verify it.

    By the way, what's your application environment ? Why you want to work 300ms after power down?

    It's not a good way to do this. The circuit may may power up with a big input cap.  

  • 0 in reply to Vental Mao
    Expert 1555 points

    hello，thank you reply to me so quickly!my system is for Subway passenger information system,now the supply power is dc 24V ,i want to generate 5V and 4.2V for imx6,can you introduce to me a device  with 300ms Vout Hold-up Time function when power off and output current 3A ,if there is not ,just introduce some close to my demand,i still can't calc the value of cap ,could you tell me more detail ?finally,can you reply to me quickly?

  • 0 in reply to user4973896
    TI__Expert 5745 points

    I'm sorry, I don't know which part can hold-up time.

    And for this, the calculate value of the cap is more than 0.4F which is a really big cap. I'm not sure the IC can work well in such a big cap, you can have a try.