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LTM4646 feedback divider

In datasheet first output uses one internal resistor and one external resistor for feedback divider. Second output uses one internal resistor and two parallel external resistors for feedback divider. Is there any reason for using two parallel resistors and not one? Did i miss something?

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  • Hi Nus 

    Vout 2 is using 3 resistors for a remote sense divider network. The ground of RFB2 should be place close to the terminals of the load.

    Regards,

    Mikee

  • Hi Mikee

    This RFB2 || RFB3 design has been my question.

    If we need 1.5V output on Vout2, can we use two 30K for RFB2 and RFB3 ? we notice that the values in datasheet Table 1:  40.2K||24.3K = 15.1K, equal to two 30K in parallel. I think RFB2 and RFB3 could be other values as long as they have a equivalent parallel value of 15Kohm.

    Is somewhere of my understading wrong? 

    3. Another question, We are layout now. To use the remote feedback, I think RFB1/2/3 should be placed nearby LTM4646, but the trace  VOUTS1/VOUTS1- and VOUTS2/VOUTS2- should be routed from remote LOAD points as two differential pairs. How do you think? 

    Thank you very much !

     

Reply
  • Hi Mikee

    This RFB2 || RFB3 design has been my question.

    If we need 1.5V output on Vout2, can we use two 30K for RFB2 and RFB3 ? we notice that the values in datasheet Table 1:  40.2K||24.3K = 15.1K, equal to two 30K in parallel. I think RFB2 and RFB3 could be other values as long as they have a equivalent parallel value of 15Kohm.

    Is somewhere of my understading wrong? 

    3. Another question, We are layout now. To use the remote feedback, I think RFB1/2/3 should be placed nearby LTM4646, but the trace  VOUTS1/VOUTS1- and VOUTS2/VOUTS2- should be routed from remote LOAD points as two differential pairs. How do you think? 

    Thank you very much !

     

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