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LM5001: LM5001

Karan
Prodigy 100 points
Part Number: LM5001

Iam Planning to use LM5001 in isolated flyback controller (DCM) topology. iam planning to charge a battery pack of 74V with this converter. i need only the current regulation to happen and i don't need voltage regulation ( CV at output of flyback ). Is it fine if i connect both COMP and FB pins to ground to achieve this desired operation?. Or may i know if its not possible by above method, what could be the best solution. What could be the best config of COMP and FB pin's to charge a 74V battery from it 

  • 0
    TI__Guru 68535 points

    Hi,

    Thank you for considering the LM5001.  Do you want to regulate the charging current to the battery?  How much current?  When does the charging current must stop?

    Thanks,

    Youhao Xi, Applications Engineering

  • 0 in reply to Youhao Xi
    Prodigy 100 points

    Hii Sir,

    1) Yes i want to regulate the charging current to battery.

    2) i want to do Input current regulation of around 1A. ( And my Vin (Max) = 4.2V ) 

    3) My maximum battery charge voltage is 74V and the operating range is from (60V to 74V) i.e.. i should charge battery from 60V to 74V. And when battery reaches 74V, iam thinking that the IC can be turned off by ENABLE PIN. ( which is controlled by a microcontroller ).Iam confused with the COMP and FB pins configuration. What can be the best arrangemet to achive the operation mentioned ?

    I have a flyback transformer designed for

    1:20 turns ratio with ( Lpri = 44uH or 25uH).

    Vin (max)= 4.2V & max input current should be regulated to 1A

    Vout(Max) = 74V 

    Can LM5001 be used for this application? if not, may i know the replacement for this? And is transformer ( Lpri )  sufficient ? 

    Thankyou

  • 0 in reply to Karan
    TI__Guru 68535 points

    Hi,

    This sounds like an interest application. I think you mean your output voltage should be regulated at 70V.  During charging, you would like to charge in constant current, and your input current must be limited at 1A or below.  Are my understanding right?  A simple flyback may not be able to achieve all these, and additional external circuits are needed. Below is one idea:

    • Set your flyback output regulation to 70V.  Use a resistor divider to monitor your battery voltage, and monitor through the FB pin.
    • Place an RC network between the COMP and FB pins for the loop compensation.  This will stabilize your voltage loop.
    • Employ a sense resistor at the battery charging return path and use an op-amp to compare the charging current by pulling down the COMP pin via a blocking diode.  So COMP can only be pulled down by the op-amp.  If no resistor is allowed on ground, then you can employ an TI INA part to sense and regulate the charging current,
    • Do the same for the input current, also use an blocking diode to be able to pull down the COMP pin.

    Operating principle:

    • When you batter voltage is inadequate, the FB will try to push COMP high but the output current control op-amp will hold COMP to regulate the charging current to your setting point.
    • When your input current reaches the setting point, the input current limit op-amp will start to pull down COMP to regulate the input current.
    • When the batter voltage reaches 70V, the FB reaches the setting point and the controller itself will reduce COMP to regulate the output voltage at the setting point. 

    Hope this clarifies.


    Thanks,

    Youhao Xi, Applications Engineering