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LM5050-1: Hot swap leakage curent

Victoria Qin
Intellectual 2620 points
Part Number: LM5050-1
Other Parts Discussed in Thread: LM5050-2

Hi team,

My customer is using LM5050-1 for redundant power supply. The schematic is as below.

When P12V_MB1 is removed and P12V_MB2 is normal operation, the ouput PIN P12V is normal, but P12V_MB1 (IN pin) has 7V stable voltage(not decrease by time) . Same situation when P12V_MB2 is removed, the P12V_MB2 has 7V voltage. 

I notice in datasheet that, when IN pin is floated and VS is powered, there is about 50uA current leak out of IN. So is it the reason why there is a 7V voltage when power is removed? Is it a normal phenomenon and if not how to avoid it? 

Thanks

Victoria 

  • 0
    TI__Guru 57737 points

    Hi Victoria,

    Please refer to the below e2e FAQ for more understanding on this topic. 

    LM5050-1: LM5050-1 Leakage Current: 

    https://e2e.ti.com/support/power-management/f/power-management-forum/994560/faq-lm5050-1-lm5050-1-leakage-current

  • 0 in reply to Praveen GD
    TI__Intellectual 2620 points

    Hi dear,

    Thanks for your reply.

    I notice in that FAQ

    ‘Either nFGD can be left open if not used or connected to IN/OUT through pull up resistor. Additionally this would not require PCB changes and hence recommended for designs that are close to mass production or at mass production.'

    In LM5050-2 datasheet, it says, it requires an external pull-up resistor to a voltage not higher than 5.5V, can it be left open? And, in my customer's system, the power rail is 12V, which is higher than 5.5V, can it use a pull-up resistor to IN/OUT? This might bring change to customer's PCB.

    That FAQ also mentioned,

    'This leakage current is not desirable in many applications such as battery powered rails where leakage current depletes the battery.'.

    Does it mean this leakage current depletes the PS2 battery? Because PS1 has been removed.

    Looking forward to your reply.

    Victoria

  • 0 in reply to Victoria Qin
    TI__Guru 57737 points

    Hi Victoria,

    The nFGD pin is rated for a Abs Max voltage of 7V and a recommended operating voltage of 5.5V. So, the  nFGD pin can be connected to IN/OUT through pull up resistor if the max IN/OUT voltage is less than 5.5V. Otherwise, you can leave the nFGD pin floating.

    Please refer LM5050-1 datasheet snapshot below. When IN is floating and VS is powered, there will be continuous leakage current from IS VS pin to GND. If the PS2 is a battery, then he battery can drain due to this continuous leakage current into the IC and it is GND. 

  • 0 in reply to Praveen GD
    TI__Intellectual 2620 points

    Hi Praveen,

    Praveen GD said:
    If the PS2 is a battery, then he battery can drain due to this continuous leakage current into the IC and it is GND. 

    If PS1 and PS2 are batteries, when PS1 OFF and PS2 ON, does the leakage current drain both batteries? Does the leakage current have influence on the under LM5050-1? 

    Looking forward to your reply.

  • +1 in reply to Victoria Qin
    TI__Guru 57737 points

    Hi Victoria,

    The leakage current is present when IN pin of LM5050-1 is floating. This means that that the PS1 battery is completely isolated and there is no chance of it being darined.