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UCC39002: About load current sharing accuracy and LS pin

Part Number: UCC39002

Hi,

Could you tell me about relationship between current accuracy and LS pin of UCC39002.

Is there a possibility of affecting the load current sharing accuracy by connecting a resistor or capacitor between the LS pin and GND?

Best Regards,

Yuto Sakai

  • Hello Sakai-san

    The LS pin should not be loaded in any way - so no resistor or capacitor to ground.

    The current sharing accuracy at full load is 1% and this is normally good enough. As the current reduces the accuracy will normally get poorer but this is not  a problem because the individual power modules in the sharing arrangement are operating at less than full power.

    Given that the graph of sharing accuracy versus current is a straight line then differences in the gain and offset values of the individual current share circuits will cause current imbalances. These could be corrected by external trimming circuits - possibly under digital control or else trimmed manually. But to be honest, this level of complexity isn't worthwhile in most applications.

    Regards
    Colin

  • Hi Colin-san,

    Thank you for your reply.

    They are concerned about whether the current sharing get poor 

    because the response speed of the amplifier inside the LS pin is slower than the response speed of the amplifier inside the CS + pin and the CS- pin.

    They think that it can be improved by changing the external resistance value or capacitance value.

    Also, They think that slowing down the response speed by resistors and capacitors connected to the outside of the LS pin may make the current sharing poor.

    Will not you give me your view on these?

    I would like to explain not to connect resistors or capacitors to the LS pin after answering the above contents.

    Best Regards,

    Yuto Sakai

  • Hello Sakai-san

    The control bandwidth of the UCC39002 is inherently low - it must be lower than the bandwidth of the control loops in the individual power modules in the power share system - this is explained in the datasheet and worked examples are in the MathCad worksheet for this device.

    In general, there is only a limited ability to improve the bandwidth of the current sharing system -

    The LS connection must not be loaded in any way - this connection is compensated internally in the UCC39002 and any RC networks on the LS line can cause instability.

    Regards

    Colin