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LSF0108: VREF_A Sink Current

IDK
Intellectual 290 points

Part Number: LSF0108

Hi,

The LSF's Understanding the Bias Circuit for the LSF Family video says:

"It is very important to note that current will be flowing into the A-side supply during normal operation, and not all voltage sources can sync current.

So be sure that your design can handle this current. The current that's being conducted through the reference FET will force a voltage from VREF A to VREF B, which will be the FET's threshold voltage."

With that said, how much current will VREF_A be expected to have to sink? In other words, what is this threshold voltage and what is the resistance through the FET?

Thanks,
Matthew

  • 0
    TI__Guru 61061 points

    Hey Matthew,

    The current sinking into the  A-supply can be calculated as (Vcc1-Vcc2-Vtn)/Rbias, where VCC1 is the higher voltage, Vtn is the 0.8V and Rbias is the 200k resistor.

    The threshold voltage is about 0.8V (hence the requirement that VrefA must be 0.8V less than VrefB) and the resistance of the FET when it is in the on state is characterized in the datasheet. Please see the below:

    Thanks,

    Jack