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LTC4353 Permits reverse current

Hello,

We are using a circuit where it gets Power from two supplies and have implemented LTC4353 for reverse current protection. Such that one of the Source(Battery) does not get loaded.

We found issues that the mosfet M1 and M2 ( We used different mosfets instead of Si4126DY used in datasheet ) both are getting Switched ON at some conditions when Only ONE power supply is present allowing for reverse current. 

Please find the attachment of How it is working for us.

LTC4353 Circuit also allows Current sharing when both Supply's difference vary in mv considering that the 

Mosfet has Body diode. But this is okay for us.

please provide us solution.

Regards,

Raj.

  • Hi Raj,

    Just to understand your question correctly, for the attached schematic,

    1.   When you apply 12V on Vin1 pin and 0V on Vin2 pin, you are seeing a voltage on the Vin2 pin. Voltage on Vin2 is following the voltage on Vin1 node that is if Vin1 voltage goes up, Vin2 voltage goes up and vice versa. Is this correct? 2.   Can you tell me the voltage level at Vin2 pin when Vin1 has 12V on it.  

    3.   Are you seeing this on a board or in a simulations? Is this LTSpice simulation? If so, can you send me the LTspice file.

  • Hello Manpreet,

    1. We did not use any LTSpice simulation and we tested this schematics on board.

    2. Yes Exactly. Vin1 is used and Vin2 is open. When Voltage on Vin1 is at 12v,I could See Voltage around 11.80 to 11.99 at Vin2.

    The Mosfet should be at off state but it does not. Its not getting heated,gate pin is not floating concluding that its not Partially ON either.

    Regards,

           Raj.

    Sent from Mail for Windows 10

  • Hi Raj,

    Do me a favor and check the connection of MOSFET on GATE2 and make sure that the DRAIN of the MOSFET is connected to VOUT and SOURCE is connected to VIN2 terminal. I am suspecting that MOSFET on the GATE2 is connected in reverse order, that is DRAIN of the MOSFET is connected to VIN2 and SOURCE is connected to OUT2. Doing so, body diode of the MOSFET on GATE2 will always conduct from OUT to Vin2. So even if GATE2 is pulled low, current will keep on flowing from the OUT through body diode of the MOSFET on GATE2 to Vin2 terminal and you will see a voltage at VIN2 terminal which will be equal to  (VOUT - forward drop across the body diode).

    Regards,

    Manpreet 

  • Hello Manpreet,

    Yes I have checked the connection twice.

    One more issue I got is I could see another Mosfet's gate is partially ON in the sense I could measure around 4v.

    This is causing for the reverse current making a low Rds on value.

    Body diode becomes useless when the Mosfet is partially Switched ON.

    I replicated the Application circuit correctly and also provided a capacitor with a capcitance at CPO1 = x10 gate capacitance of Mosfet ( CISS ) as mentioned in datasheet.

    Regards,

    Raj.