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PMP9444: 49R9 resistor for SENSE+ input of LMZ31503, LMZ31506 and LMZ31710

Marian Krivda
Prodigy 120 points
Part Number: PMP9444
Other Parts Discussed in Thread: LMZ31506, LMZ31710, , LMZ31503

Hello.

Could somebody explain what is purpose of 49R9 resistor for SENSE+ input of LMZ31503, LMZ31506 and LMZ31710 on the PMP9444 schematic capture.

If I use it for 3.3V then I see 100 mV difference i.e.3,4 V which is absolute maximum for Xilinx Kintex Ultrascale.

I didn't find such recommendation in datasheets of mentioned DC-DC converters.  

Marian

  • 0
    TI__Expert 5685 points

    Hello Marian,

    The 49.9 ohm resistor are for remote sense.  The SENSE+ input needs to be connected at the load.  The 49.9 ohm resistor provides a local connection just for protection purposes incase the trace is not connected or something happens to that feedback path, there is a local connection.

    There should not be a 100mV difference in the output voltage at the load.

    Thanks,

    Robert

  • 0 in reply to Robert Taylor1
    Prodigy 120 points
    Hello Robert.

    Thank you for response.

    SENSE+ input is connected through 49R9 resistor (serial connection) to load, so there is voltage drop on this resistor (100 mV for 3.3V).
    For local protection, 49R9 should be connected in parallel i.e. between SENSE+ and VO, and SENSE+ should have direct connection to the load.

    Marian