• State TI Thinks Resolved
  • Locked Locked
  • Replies 2 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 147 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.

LMR43620-Q1: A cap question for LMR43620MSC3RPERQ1

Rong Liu
Prodigy 50 points
Part Number: LMR43620-Q1

I am using LMR43620MSC3RPERQ1. On the page 38 of datasheet, it states "If the application is operating close to the minimum input voltage, this dip can cause the
regulator to momentarily shut down and reset. The best way to solve these kind of issues is to limit the distance
from the input supply to the regulator or plan to use an aluminum or tantalum input capacitor in parallel with the
ceramics. The moderate ESR of these types of capacitors help dampen the input resonant circuit and reduce
any overshoots. A value in the range of 20 μF to 100 μF is usually sufficient to provide input damping and help to
hold the input voltage steady during large load transients.".

My power input is 5V (USB port) and output is 3.3V. The trance length is less than 25mm. Should I still add an aluminum cap? I have a concern on vibration profile on the aluminum cap and the tantalum cap is too expensive. Thank you.  

Rong 

  • 0
    TI__Guru 57555 points

    Hello

    The issue that is mentioned in the data sheet refers to applications that are operating close to the minimum input voltage of 3.3V, or so.

    In that case a large load transient on the output of the regulator can cause the input voltage to dip below the minimum input, causing the 

    regulator to shut down, until the input voltage recovers.  This possibility will depend on many factors such as how close you are operating to the 

    minimum input voltage, the effective impedance of your input supply, the severity of your load transient, and the amount of input capacitance.

    In your case, operating at 5Vin, you have about 2V of head room.  It would seem that would be adequate to prevent any issues with the device

    shutting down from under-voltage.

    However, if you have any doubts it would be best to test with your specific USB input and expected load transient.

    Keep in mind that using an Al. electrolytic on the input can also help to damp any EMI input filter that you may be using.

    Thanks

  • 0 in reply to Frank De Stasi
    Prodigy 50 points

    Got it. thank you