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TPS2412: Load sharing/redundancy in 12V high current system

Christian Ahler1
Intellectual 410 points
Part Number: TPS2412
Other Parts Discussed in Thread: UCC39002, TPS2410

Hi TI and other experts.

For a new server design we would like to incorporation a redundant power scheme constructed by two independent power supplies (instead of a ready made one). This is to make is possible to monitor what is going on. For that we need an Oring concept. It is a 12V system. 20A on each supply. Hence a total of 40A.

It has to be realized such that one supply can fail short and the other will still operate. It also has to be realized (if possible) such that load sharing is a natural part of the system. Each supply will deliver about half of the power in normal operation. 

What solution(s) should we consider. TPS2412? There might be other that are better suited for a 12V "high current" system.

Thanks in advance. 

Best, Christian

  • 0
    TI__Genius 16305 points

    Hi Christian,

    TPS2412 is best suited for ORing 12V power rail at 20A each.

    However, when it comes to load sharing TPS2412 it better than having two schottky diodes, because forward drop of schottky diodes have a negative temperature coefficient. Here it can lead to a situation where only one 12V rail takes bulk of the load current.

    TPS2412 has a linear ORing scheme where external MOSFETs forward drop is regulated to 10mV. This results in a better load sharing and blocks reverse completely (DC current) when the one of the input fails short.

    Please note that TPS2412 doesn't take part actively in load sharing and load sharing accuracy largely depends on the voltage difference between two 12V power supplies and to some extent PCB trace resistance due to routing mismatch. Droop sharing (internal to power supplies) is common practice to achieve load sharing. "https://training.ti.com/power-tips-parallel-power-supplies-droop-method-0" 

    For accurate load sharing, additional load share controller such as UCC39002 is required. UCC39002 controls the power supply feedback voltage / sense lines to adjust the power supply to achieve accurate load sharing.

    For load sharing, please refer to the application note "http://www.ti.com/lit/an/slua550/slua550.pdf" and to avoid hiccup issues during startup refer to http://www.ti.com/lit/an/slyt100/slyt100.pdf to 

    Regards,

    Kari.

  • 0 in reply to Karikalan Selvaraj
    Intellectual 410 points

    Thank you for your reply. 
    The solution is comprised of two complete of the shelf supplies, hence no access to feedback voltage. Do you have solutions for load/current sharing for this as well?

    Cheers, Christian

  • 0 in reply to Christian Ahler1
    TI__Genius 16305 points

    Hi

    Could you let us know by how does the two shelf power supplies output voltage differ?

    Regards,

    Kari.

  • 0 in reply to Karikalan Selvaraj
    Intellectual 410 points

    Hello again,

    This is still of importance.

    They can differ as much as allowed. What we are interested in currently is being presented/suggested different solutions. Would be great if you can assume the differ by 1V in one case and by e.g. 50 or 100mV in another case. We can based on this define the requirement for the power supplies in mention. 

    You are also very welcome to suggest different power suppliers for reference with some of you designs. The combined output should be 12V and 200 og 300W. Hence 20A ish.

    This is for a server series.

    Thanks.

    Best, Christian

  • 0 in reply to Christian Ahler1
    TI__Genius 16305 points

    Hello Christian,

    Usually 12V shelf supplies catering to the telecom market have load sharing implemented using droop sharing.

    Droop sharing is a load sharing technique implemented within shelf power supplies (in its feedback loop, you can refer to the training link)

    Most of the shelf power supplies offer this feature and you could cross check with the power supply manufacturer.

    But if the droop sharing is not already available in the shelf power supply, then we may have to implement other methods which may not be power efficient at 20A.

    For example lets assume two 12V power supplies differ in the DC voltage by 100mV, one is 12.0V and other is 12.1V, then to enable load sharing equally between the two, the power dissipated due to 100mV voltage difference between the two supplies has to be considered. At 20A total power, 10A will be taken from each supply and the second one with 12.1V will have to dissipate 100mV * 10A = 1W of power. This amounts to 0.4% of power loss at 240W power. Would this be acceptable?

    If this is acceptable, we can work a solution that enables load sharing with TPS2410 or preferably LM74700.

    Regards,
    Kari.