• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 2 answers
  • Subscribers 62 subscribers
  • Views 389 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

TPS43060: DCR current sensing values

Nitish Agrawal
Expert 1595 points
Part Number: TPS43060
Other Parts Discussed in Thread: LM5121

Hello,

I am trying to implement DCR current sensing when using TPS43060 as boost controller.

Per my calculations:
Vcs_max_typ = 0.0695 V (calculated based on max duty cycle, using Fig. 20 of TPS43060 datasheet)
Rcs = Vcs_max (typ.)/(1.2*I_L,pk) = 10.387mohm

Chosen inductor = 8.2uH (max DCR = 10.81mohm, min DCR = 9.83mohm).

L (henry)         DCR, ohm          L/DCR =
8.20E-06         0.01                    8.20E-04                 (Figuring that 0.01ohm is a reasonable value for the inductor DCR)

Choose values of R1, C filter that lies across the 8.2uH inductor):
R1 (ohm)        L/DCR                C (calculated)
1000               8.20E-04            8.20E-07

Per the 2014 How2Power article by Haifeng Fan, I plan to use a 1kohm compensating resistor to negate the offset caused by the 70uA bias current of the current sense inputs..

Are the R1 and C values above reasonable?
Can I use these as the final values or do I need to consider anything else (such as the gain of the current sense amplifier, etc.)  or any other elements?

Regards,
Nitish

  • 0
    TI__Guru* 78630 points
    HI Nitish,

    Once the time constant matches, it should work. So you selections are okay.

    Good luck in your project.

    Thanks,
    Youhao Xi
  • 0 in reply to Youhao Xi
    Expert 1595 points
    Hi Youhao,

    Thank you for your response. A couple more questions:

    1) What is the acceptable level of ripple in the voltage being fed across ISNS+, - ISNS- pins?

    2) Is there a recommended way to limit inrush current into the boost converter from the input supply when using TPS43060?

    Kind regards,
    Nitish Agrawal
  • 0 in reply to Nitish Agrawal
    TI__Guru* 78630 points
    Hi Nitish,

    The current sense amplifier is fast device, and the maxim ripple across these two pins is 50mV, or it will trip the peak limit.

    If the inrush is mainly caused by load, then you can increase the SS capacitor to slow down the start up. If the inrush is mainly caused by charging the output capacitor during input application, SS will not help. In such case, you should consider the LM5121, or add a hotswap device at the input of the boost stage.

    The LM5121 has the inrush limit function integrated, and please take a look.

    Thanks,
    Youhao