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TPS2546 current-limit settings

Matt Overlin
Prodigy 130 points
Other Parts Discussed in Thread: TPS2546, TS3A4741, CSD17483F4

In page 31 in the TPS2546, there is an equation that gives the i_lim resistor value, which would correspond to a certain output current limit.  Using this equation: If I want my current limit to be 1.50 A, I should use: 50,250/1.5 A = 33.5 kOhms.  However, on page 29 in the example application (figure 38 .. with 2 TPS2546 chips), there is a resistor of 29.8 kOhms to set a current limit of 1.5 A.

So, 33.5 kOhms vs. 29.8 kOhms.  There seems to be an inconsistency here.  

Basically, I want to know what resistances correspond to the following current limits: 0.9A, 1.0A, 1.5A, 2.0A, 3.0A.

Thanks,

Matt

  • 0
    Prodigy 130 points
    Another question about the setting the current limits for the TPS2546:
    I want to have 2 resistors in parallel that connect the ILIM_HI pin to ground. And, one resistor will be switched in or out. I thought about using the TS3A4741, for example, to switch one resistor in and out. In this way, I can have to different current-limit settings, by controlling this switch from a microcontroller, for example.
    However, I would not like to use the TS3A4741. Instead of the TS3A4741, though, I would like to use the CSD17483F4, and control this transistor to be ON/OFF. So, I could choose between 2 current-limit settings in this way instead.
    Is it okay to use the CSD17483F4 instead of the TS3A4741 here?
    I'm not sure about what V_DS for the transistor will be as well as other things. I just don't know enough about the TPS2546 to say whether or not the CSD17483F4 will work with it like this.
    Thanks!
    Matt
  • 0 in reply to Matt Overlin
    TI__Mastermind 25045 points
    Hi Matt,

    Your post has been moved to the Power Interface - POE, Hot Swap & ORing Controllers Forum as I believe they should be able to provide you with the information that you need.

    Regards,

    David
  • 0 in reply to DavidL
    TI__Mastermind 42795 points

    Use page 31 equation to calculate the current limit.

    As for page 29 figure 38, it represents CDP/SDP PPM. 1.5A/0.9A are the continuous currents and 29.8k will guarantee a 1.5A minimum for that application.