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Original question:

LM74500-Q1: Some design question about LM74500-Q1

LM74500-Q1: What is the reverse current blocking used for?

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Intellectual 2145 points
Part Number: LM74500-Q1
Other Parts Discussed in Thread: LM74700-Q1

Dear TI,


We now want to use LM74500-Q1 or LM74700-Q1 for the reverse polarity protection.
The main difference between them is one has the function of reverse current  blocking and one doesn't.

We noticed that on the page 13 of the LM74500-Q1 datasheet (<LM74500-Q1 Reverse Polarity Protection Controller>):

(1) LM74500-Q1 is used in the “Load Driving Path”;
(2) LM74700-Q1 is used in the "Logic Path".

We are not clear that the LM74500-Q1 can be also used in the "Logic Path"?
If we choose to use LM74500-Q1, which problems will appear?


Regards,

William

  • 0
    TI__Expert 3370 points

    Hi William,

    LM74500-Q1 only provides reverse polarity protection without providing reverse current blocking, which is required to maintain charge on the hold-up capacitors connected to the downstream loads in the logic path, so that power supply to the loads could be maintained during short duration battery interruptions or battery failure events.

    Please refer to section 5 (Reverse polarity protection vs Reverse current blocking) of the following application note for further details: Basics of Ideal Diodes (Rev. B) (ti.com). Kindly let us know in case further clarification is needed. 

    Thanks and best regards

    Divyanshu

  • 0 in reply to Divyanshu Vadehra
    TI__Expert 3370 points

    Hi,

    An important addition: In case LM74500-Q1 is being sought to replace a discrete PFET based reverse protection solution, it implies that the output bulk capacitor is large enough to provide the necessary voltage to the downstream loads. In that case, LM74500-Q1 can be used for reverse protection as reverse current protection is not necessarily required and LM74500-Q1 would offer the required protection at a lower cost.

    Thanks and best regards

    Divyanshu