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TI Home » TI E2E Community » Support Forums » Power Management » SIMPLE SWITCHER® » SIMPLE SWITCHER® - Forum » LM3478 stops switching as Vin drops
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LM3478 stops switching as Vin drops

This question is answered
Nick Tseng
Posted by Nick Tseng
on Jul 12 2012 09:54 AM
Intellectual1300 points

Team,

Honeywell is experiencing a problem with their LM3478. As they drop Vin from 4.8V to 4.7V, the part stops SW and the gate drive signal stays high (100% duty cycle). I have attached a schematic and a .ppt illustrating this behavior. Another thing to note is that they are pulsing the input voltage from 0 to Vin.

Vout = 44V 

Iout < 350mA

Their voltage at Vsense (shown in slides 1 and 2) is <100mV. In the datasheet, the lower limit is specd at 125mV. I can't find what happens when you're below the lower threshold in the datasheet.

Please advise.

Thanks,

Nick3515.LM 3478.pptx

6607.LM3478 circuit.docx

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  • Giuseppe Pinto
    Posted by Giuseppe Pinto
    on Aug 07 2012 16:38 PM
    Expert3815 points

    Hello Nick,

    what's the current limit on the input power supply (the supply that generates 4.7V)?

    Regards,

    Giuseppe

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  • Nick Tseng
    Posted by Nick Tseng
    on Aug 07 2012 16:51 PM
    Verified Answer
    Verified by Nick Tseng
    Intellectual1300 points

    Giuseppe,

    Sorry for not closing this out. You actually provided the answer to me on this via email (attached).

    8182.RE SperianHoneywell LM3478 support.msg

    Thanks,

    Nick

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