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LM43600: Reference Design PMP9546 - will the battery discharge through the charger if powered down

Don Edvalson49
Prodigy 230 points
Part Number: LM43600

Looking at reference design PMP9546  (Schematic at http://www.ti.com/lit/df/tidr919/tidr919.pdf ) I have a question that needs some information about the internals of the LM43600. If the power supply is shut off, but the battery is still connected, will the battery discharge through L1 and back into pins 1 and 2 of the LM43600? I am wondering if a diode is needed between L1 and the battery?

  • 0
    TI__Mastermind 27030 points

    Hi Edvalson:

    Your analysis is right, the battery need to be disconnected or add a diode to prevent current go back to input through L1 and body diode of internal mosfet to input.

    Thanks


    Daniel Li

  • 0 in reply to Daniel Li14
    Prodigy 230 points

    Thanks for your response.

    I assume the zener diode would connect after the blocking diode (directly to the battery) so that the forward voltage drop of the diode does not change the charge voltage. Does this seem correct to you?
    Don
  • 0 in reply to Don Edvalson49
    TI__Mastermind 27030 points

    Hi 

    zener diode is proivde constant votlage in  no load current or light load condition when battery votlage is charged nearly full. so no matter you put the zener diode bofore or after the diode. it is only to prevent when the sensed current lower than FB, the voltage will raise until 7.8V(6.8Vzener+1V FB)

    Zener also has some variation compare to diode voltage drop, so it can't be used accurate control the votlage at feedback point.

    Thanks

    Daniel Li