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LM66100: Need for FET on a Input Polarity Protected part?

SmartEnrg
Expert 1145 points
Part Number: LM66100
Other Parts Discussed in Thread: TIDA-010224, , , TPS22919

Referring to TIDA-010224 - Low-Power Wireless Camera Reference Design

I see there's (Q1) SI2323DS in front of (U3) LM66100DCKT input pin

LM66100 datasheet describes it as "5.5-V, 1.5-A 79-mΩ, Low IQ Ideal Diode With Input Polarity Protection"
Why Q1/FET is needed/ used in addition to U3's Input polarity protection?

I see it (the FET) is not used in LM66100EVM - so even more curious...

Please advise. Thanks.

  • 0
    TI__Genius 13260 points

    Hello,

    I am looking into this and will get back to you by EOD tomorrow. 

    Regards,

    Kalin

  • 0
    TI__Genius 13260 points

    Hello,

    The purpose of the PMOS is to provide RPP. The LM66100 function here is set up to be Dual Ideal Diode ORing for continuous output power. It is not used to provide RPP due to V_VBAT being another path that the LM66100 doesn't feed. The TPS22919 doesn't provide reverse polarity or reverse current protection so the PMOS is needed. 

    Regards,

    Kalin

  • 0 in reply to Kalin Burnside
    Expert 1145 points

    Thanks Kalin,

    If I understand you correctly - the reason PMOS isn't needed to protect (2x LM66100) OR'ed section, but because V_VBAT is extended out to U20 and TPS22919 doesn't support RPP, is that correct?
    In other words - if my application (unlike TIDA-010224) Only require single supply VBAT, derived from either Primary Batt (3.6V), or USB (5V),  automatically switching between the two (LM66100). That's it! In that situation - I do Not need PMOS (just like in LM66100EVM design), right?

  • +1 in reply to SmartEnrg
    TI__Genius 13260 points

    That is correct. Without the battery gauge circuit between the supply and the LM66100 device there wouldn't be a need for the PMOS. 

    Regards,

    Kalin