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LM5051: Combine High side and low side Oring Fet controllers in circuit

Dirk-Jan Vethaak
Prodigy 40 points
Part Number: LM5051
Other Parts Discussed in Thread: LM5069, TPS3711, TPS3701

Dear engineers,

I am looking for a solution for the problem below:

Have a  primary and backup powersupply of 24V 3A, worst case scenario is the both grounds are not connected to each other. ( floating) .

When the primary voltage drops a certain level the systeem needs to switch over to the backup power and switch off the primary supply input.

Hereby the positive side and negative ("gnd") must be changed . ( low side is needed to protect against difference in the floating "gnd" and avoid gnd loops in the wrong return paths / cables)

1) I saw the LM5050 and LM5051, Is it possible to combine them ?    

2 ) Or is there an other solution , prefferable with inrush limiter. ?  like LM5069 

Note: I dont want to use a double switched relay.

Kind regards,

Dirk-Jan Vethaak

  • 0
    TI__Genius 16305 points

    Hi Dirk,

    Yes you can use LM5050 and LM5051 together.

    For the scenarrio when both the grounds are not connected to each other(floating), then LM5050 would do the job of switching over to available supply.

    But LM5051 will help mainly to block any reverse current in the ground loop that could be formed.

    Could you give a pictorial representaiton of the system diagram you plan to implement so that we are on the same page.

    Regards,
    Kari.

  • 0 in reply to Karikalan Selvaraj
    Prodigy 40 points

    Hi Kari,

    hereby an overview:

    Redundant Power supply:

    There is one primary power supply and a backup. Only one of them will be switched on. Both grounds are floating and the cables to the power supply are long enough which can cause ground loops.

    If the primairy power supply is ok then the power switches SW 1 high and low will be closed and SW2 High and low will be open. Otherwise the switches will be switched opposite.

    A deadtime is needed, so there will be no overlapping of both power supplies / GND. (1-5 ms) during falling or rising edge.

    The supervisor ic can be the TPS3701 or TPS3711.

    I saw that the body diode from the mosfets in combination with lm5050  lm5051 still allow current to flow , which i don't prefer. 

    Maybe there are other IC's which can solve this problem beside chips discribed earlier? 

    Kind Regards

    Dirk-Jan