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Equivalent LP3855 with current limit?

David Jones98655
Prodigy 110 points
Other Parts Discussed in Thread: LP3855, LMP8646

Hi -


I'm currently using an LP3855 for a 5V output with loads varying from 2A-100mA.  I want to limit the load to 1A partly to prevent the regulator entering the overcurrent protection, partly to protect my battery source. 

Is there an alternative to the LP3855 you'd recommend?  Alternatively is there an additional current limit circuit you'd recommend?

Many thanks,


David

  • 0
    TI__Mastermind 22610 points

    Q1: Is there an alternative to the LP3855 you'd recommend?

    A1: Possibly, but I'm not clear on the contraints set by: "... I want to limit the load to 1A ..." and yet "... loads varying from 2A ..." and "...  prevent the regulator entering the overcurrent protection ...".

    Q2: Alternatively is there an additional current limit circuit you'd recommend?

    A2: The just released LMP8646 Precision Current Limiter is a possibility for a 'roll-your-own' current limit scheme. The down-side is that the output of the LMP8646 need access to the LDO ADJ feedback pin, and I presume that you are using the LP3855ET-5.0 which will not work with the LMP8646.

    See Figure 17 in the LMP8646 datasheet ...

    http://www.ti.com/lit/ds/symlink/lmp8646.pdf

     

  • 0 in reply to Donald Jones
    Prodigy 110 points

    Apologies for ambiguity:  I'm using the LP3855 to power a modem with large capacitors to smooth peak loads, however they're a 0ohm load when they start charging - hence I want to limit the current through the LP3855.

  • 0 in reply to David Jones98655
    TI__Mastermind 22610 points

    A 5V LDO with a maximum short circuit current limit less than 1A. The next question would be: what do you need for continuous operating current?

    The LP2954IS/T has pre-set 5.0V at 250 milli-A output, with a short circuit current rating of 380 milli-A typical and 530 milli-A max.

    A lower short circuit current will need more time to charge the large capacitors to the final voltage.