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What is the correct resistor for the power supply design at http://www.ti.com/lit/ug/sluub69a/sluub69a.pdf?

Otto Hunt
Expert 1475 points

The power supply here has the label LLC_RCS connecting 1.2 ohm sense resistors R7, R8, and R9 to R55 which is a 2.21K resistor, the other side of which goes to U6 pin 11. It makes no sense to put that 2.21K resistor in series with low-value sense resistors. Surely this is an error. What should it be?

  • 0
    Expert 1475 points

    Well, gee, I kept staring at the circuit and finally made a little sense of it. (Splitting the diagram into two sheets does not help!) There is a label "LLC_RCS" near the source of Q3. The three parallel sense resistors R7, R8, and R9, sense current flow from Q3 source to PGND. So R55 in combination with C39 is an input spike filter for U6 pin 11.