• State TI Thinks Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 2 answers
  • Subscribers 63 subscribers
  • Views 550 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TPS563200 - Inductor DC resistance value

Michael Hochmuth
Prodigy 60 points
Other Parts Discussed in Thread: TPS563200Part Number: TPS563200

Application: Power for clocked illumination

Question type: Development and troubleshooting

Support topic: /Other topics/Design techniques and how-to guides/

Description of the problem: Hello,

we have an application to realize 3.3V from 12V. We are clocking a VCSEL-array with 20...30MHz and a duty cycle of 50% over a burst time up to 5ms. The repeat rate is 25ms. In the burst the average current is ca. 2.5A. In our evaluation we had used the TPS563200 with WE-LHMI 74437324022 and all works well. We cannot use an inductor larger than 5x5x2mm³. The input inductande ist 22µF, the output has 47µF, than an ferrite and again 4x47µF MLCC to stabilize the supply for the VCSEL array.

Now I tooked then Webench to simulate something and it says that the DC resistance must be lower than 16mOhm. In the datasheet is no maximal DC resistance mentioned.

Is there a problem in stability of the circuit if the DC resistance of the inductor is 50...90mOhm, or is it only relevant for the efficiency.

Regards
Michael Hochmuth

  • 0
    TI__Expert 4875 points

    HI Michael,

    I got a little bit confuse for this description here "The input inductande ist 22µF, the output has 47µF, than an ferrite and again 4x47µF MLCC to stabilize the supply for the VCSEL array." Is 22uF and 47uF for input and output inductor or for capacitor? The unit for inductance should be H. I think you want to mention the input and output capacitor. TPS563200 is a DCAP2 part which require low ESR output cap in application. It is different from the DCAP part which require high ESR cap. There is no need to have a large output ripple for stability since there is internal ripple injection. In this case, the low ESR cap is recommended. It is for the stabilityt.

    Best 

    Anthony

  • 0 in reply to Anthony Lang
    Prodigy 60 points
    Hi Anthony,

    sorry for the late reply, I was placed to another project for a month. Of course 22µF is not the inductance it is the input capacitor. But I want to know the stability of the design because we have no place for a large inductor with small DC resistance. In the datasheet is no hint for the maximum DC resistance of the inductor but the Webench Designer says me to use an inductor with a resistance of 16mOhm. So I dont know if it is relevant for stability or only for effectivity.
    At this time I havn't seen any problems with a DC resistance of 50..60mOhm of the 2.2µH inductor (WE-LHMI 74437324022) . But can we get problems with stability in the future? Is it possible to use an inductor with 90mOhm RDC?

    Best regards
    Michael
  • 0 in reply to Michael Hochmuth
    TI__Expert 4875 points

    Hi Michael,

    I did not see any issues with stability if using higher DCR. If higher DCR indcutor selected, which means lower quality factor filter, the damping factor will be bigger. It only leads to smooth change of phase around resonant pole on bode plot. For DCAP2 part, there is a zero placed after resonant pole by ripple injection that will boost phase towards 90 degree. In this case, the phase will have enough margin around crossover frequency. No stability issue but only lower efficiency will have if bigger DCR inductor is selected. 

    Best,

    Anthony

  • 0 in reply to Anthony Lang
    Prodigy 60 points

    Hi Anthony,

    thank you for the explanation. This will help me.

    Best regards

    Michael