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TPS55340: How to choose a proper value for FB resistor?

Stephen Zhu
Prodigy 10 points
Part Number: TPS55340

Hello,

As we need to reduce the quiescent current of TPS55340 block, can we set the upper FB resistor 345K and the lower one 36K?

The input voltage(9V) of TPS55340 will always on when the product in sleep mode.

As a boost function group, there is a diode[D1 in reference schematic] connected from input to output. So the FB resistors are always powered by 8.5V.

The spec of I_fb is 1.6nA(Max 20nA).

So the combination of 345K/36K is a risk?

Thanks

Stephen

  • 0
    TI__Guru 65400 points

    Hello Stephen,

    Please have a look at this app note: Design considerations for a resistive feedback divider in a DC/DC converter

    In general you need to keep in mind that the resistors of the feedback divider influence stability.

    If the resistor values are really high, you need to calculate them with the additional information of the current flowing into the device. This current is flowing through the top resistor, but not through the bottom one, so you need to use Kirchhoff's law instead of the simple formula that ignores the current into the IC. But I expect that this is not yet necessary with the resistor values and FB current above.

    Best regards,
    Brigitte