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LM66100: Supply ORing with 2xReverse Current Blocking configuration

Baptiste Bainier
Prodigy 135 points
Part Number: LM66100
Other Parts Discussed in Thread: TPS2116

Hello, 

Due to our tight layout, we tried to implement supply ORing with 2*RCB configuration (see the schematic attached).

It seems that the LM66100 lets the current go from Vout to Vin even when Vin is powered off, which is a big issue to us. 

Maybe there is something we missed in the datasheet ? Is it normal that this circuit doesn't work ?

Here is a part of our Supply schematics; the power can come from either 12V supply or Lithium cell. In case both are present, the 5V generated from the 12V supply (IC10) is higher than the 5V from the cell (IC11), giving it higher priority on the 5V out rail and enabling the Cell charge (U6).

Problem is when only cell is present, 5V goes through D8 and powers the cell charge and the 12V rail through the IC10 buck...

Thank you, 

Best regards,

Baptiste. 

  • 0
    TI__Mastermind 32650 points

    Hi Baptiste,

    LM66100 cannot be effectively used to OR and RCB at the same time. The reference that turns off the device is the CE voltage. This means that the CE voltage has to rise over the VIN voltage by a specific amount to turn off the device.

    If you note our turn on and turn off specifications, when setting the device up in an OR-ing circuit the devices work in a break-before-make topology (turn off one device before turning on the other). By connecting the system like this, you are dependent on the RCB protection being triggered to turn off the device. This means that up 0.5A or more could flow in reverse before enough voltage is generated across the FET for the device to recognize it as a reverse current event. This is because even though the turn off voltage is 35mV, the R_on of the FET is around 70mOhm.

    I would recommend changing the topology to be more like OR-ing as stated on the datasheet or to use an integrated device like TPS2116 that provides internal back to back FETs (to protect against reverse current events) and two channels to one channel MUXing with the option to set priority at specific voltages.

  • 0 in reply to Shreyas Dmello
    Prodigy 135 points

    Hello, 

    Indeed, we could verify that. Thank you for the answer and the PowerMUX suggestion,

    Best regards, 

    Baptiste