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LM7480: Differences between LM7480, LM7481 and LM74502

fedi makni
Prodigy 50 points
Part Number: LM7480
Other Parts Discussed in Thread: LM7481, LM74502,

Tool/software:

Hello,

I am currently designing a protection circuit for our device. Our device operate at 48V with output current of around 8A
We would like to protect it from:

Reverse polarity

Inrush current

OV

We thought about using an ideal diode for that task as we check texas instrument website and the used filter option we came across 3 different parts LM7480, LM7481 and LM74502.

Other than the fact LM7481 has higher gate drive current we couldn't find significant differences between them in order to select the appropriate part.

Could you share with us any that we may miss in order to choose a suitable one?

Additional thing we want to confirm is that those devices doesn't have an overcurrent protection feature as while checking on the parametric search in digikey the output current is set to 5A so we want to make sure.

Thank you for your support.

Best regards

  • 0
    TI__Mastermind 47280 points

    Hi Fedi,

    LM7481,LM7480 has an additional feature of reverse current blocking as compared to LM74502.

    These devices do not have over current protection integrated.

    Regards,

    Shiven Dhir

  • 0 in reply to Shiven Dhir
    Prodigy 50 points

    Hello,

    Thank you for your reply.
    We chose to use the LM74800-Q1 for our application and i would like if you can assist me to understand couple of parameters in the datasheet.
    To limit inrush current we need to add a cap (Cdvdt) the formula is as shown in the picture below

    • For Cout is the total expected capacitor at the load correct?
    • Iinrush is the max inrush current allowed to go through the mosfets (for example if our load is expected to draw 8A we can set Iinrush to 10A for example) correct?

    • Any formula for the added resistor in series with Cdvdt?

    Another request is regarding the mosfet selection, in page 24 there is a Maximum gate-source charge of 43nC, does that mean any mosfet with higher gate-source charge cannot operate optimally or only the active rectification will be poor?

    Thank you for your support.

    Best regards.

  • 0 in reply to fedi makni
    TI__Mastermind 47280 points

    Hi Fedi,

    Yes, COUT is the total load capacitance.

    Inrush is the max current during output capacitors charging. It is not the max total load current.

    Resistor can be kept fixed at 50-100ohms. I doesn't have an influence in inrush current calculation.

    Higher Qg mosfets can be driven. But Active rectification performance will be affected.

    Regards,

    Shiven Dhir

  • 0 in reply to Shiven Dhir
    Prodigy 50 points

    Hello,

    Thank you,

    So Iinrush is the acceptable max current we want to allow at the start-up of the system correct? To make sure if our system operate at 8A for example it will be a value slightly above the 8A or even 8A if we don't want to allow inrush current and that cause a slow turn on.

    Because i saw in the datasheet that for some calculation you used 250mA which make me wonder.

    Another point is as in our application it is a little hard to estimate the load capacitance is there a max value we need not to exceed or something like that? 

    Looking forward to your reply.

    Best regards.

  • +1 in reply to fedi makni
    TI__Mastermind 47280 points

    Hi Fedi,

    Yes, its the maximum current allowed at startup. Datasheet used 250mA maybe just an example. You can setupup 8A inrush limit as well. Please not that MOSFET has to be strong enough to handle 8A inrush.

    There is no maximum value of load capacitance. As far as the MOSFETs can support its charging, any value is fine.

    Regards,

    Shiven Dhir