• State Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 2 answers
  • Subscribers 62 subscribers
  • Views 511 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.

TPS92515: Selection of Rsense

na na78
Guru 16770 points
Part Number: TPS92515

Hi

How to consider the rating of Rsense?

We suppose to be Vin=30V and ILED = 1.2A.

Could you please show us the way to estimate?

BestRegards

  • 0
    TI__Mastermind 28655 points
    Hello nana78,

    This is in the datasheet. See section 8.3.1 for an explanation of how the TPS92515 regulates current and how to calculate Rsense.

    Basically Rsense is sized for Vcs/Rcs = Iled + (1/2)Ipeak2peak. You have to know what the peak to peak current ripple is to calculate Rsense.

    Regards,
  • 0 in reply to Irwin Nederbragt
    Guru 16770 points
    Hi Irwin

    Thank you for your reply.

    Regarding to power ratings, can we obtain as Power = Rsense * [Iled+(1/2)Ipeak2peak ]^2 ?

    BestRegards
  • 0 in reply to na na78
    TI__Mastermind 28655 points

    Hello,

    That result will be larger than the actual power but can be used to size the resistor.

    Power = Rsense * [Iled+(1/2)Ipeak2peak ]^2*maximumdutycycle.  If the maximum duty cycle is 50% then the power rating will be half of the equation without the dutycycle in it.

    Also, if the current ripple is a high percentage of the average current you would have to look up the equation for calculating RMS current in the resistor or use the RMS integral equation.

    Regards,

  • 0 in reply to Irwin Nederbragt
    Guru 16770 points
    Hi Irwin

    Thank you for you reply.

    I made example, could you please check this?


    Rsense : 0.2ohm
    ILED : 0.35A
    Ip2p : 0.1A
    Duty(max) :50%

    Power(Rsense) = 16mW, as estimation.

    So we can select Rsense 1/16W power ratings.

    BestRegards
  • 0 in reply to na na78
    TI__Mastermind 28655 points

    Hello,

    The calculation is correct but the resistor value is wrong.  Please go through the datasheet on how to calculate the current sense resistor value.  You will need to go through the design process because it will include the inductor value, switching frequency, Vin, Vled.  You need to design the circuit to know what value the current sense resistor value will be.

    Regards,