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LM7310: Priority PowerMUXing application related query

Abhinav Adya
Prodigy 10 points
Part Number: LM7310

Tool/software:

I am working on a new project and were considering using the LM7310 for our purpose. We have two DC power supplies - An SMPS (220VAC/12VDC 50A O/P) and an AUX (12V DC O/P). Till the supply from Mains is available SMPS remains ON and the AUX replaces the SMPS when there is no power available from the mains supply. We are using the standard values of the caps and resistors as given in the datasheet. As per the datasheet, when the circuit is configured according to Priority Power MUXing, the Vout(min) when the power switches between the SMPS to the AUX is as can be seen below in cell B20,C20 and D20 for different values of Cdvdt. Since the voltages obtained here are extremely low, I wanted to know if this is a mistake in my understanding and how to rectify this error.

Thank you

Regards

Abhinav

 

  • 0
    TI__Mastermind 39315 points

    Hi Abhinav,

    It looks odd to me also when calculating using this formula. When using the power PMUX configuration, the first eFuse is turning off and the second one is doing the startup. During this transition, if the load continues to draw current, that current is provided by the output capacitor. This formula is nothing but minimum voltage supply minus the capacitive discharge during that time period. 

     This low voltage from the formula means that the capacitor won't be able to supply this much current and voltage will drop to zero very quickly. Increasing the Cout will help here (adding a bulk cap to prevent power rail drop).

    One thing I want you to check is, will the load current be 2A or less. If it is continuous 2A, then Cout needs to be increased.  

    Best regards,
    Arush