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TPS714: Selection of FB resistor

Hale Tan
Expert 3770 points
Part Number: TPS714


Hi team!

The customer wanted to use about below 1Mohm resistor as feedback resistor. Because the selected resistor type is almost below 1Mohm. But as datasheet said, we suggest the feedback resistor is as shown below. The customer needs to keep low voltage output ripple(about 30mV) and the output is 5V~7V, about 10mA. If they choose resistor below 1Mohm, what is the risk? And do you have any advice?

  • 0
    TI__Guru 50025 points

    Hi Hale,

    Do they need to keep the output voltage within 30mV of the nominal voltage with transients as well? Or do they just need the AC ripple to be less than 30mV?

    Using smaller resistors is not an issue with regards to stability and other device performance characteristics. It is generally better to use smaller resistors for improved accuracy, but the smaller resistors consume more current. This extra current does come from the output of the device so it is no different than a load, and having a minimum load helps with transient performance as well. So, if they can afford the extra current it is better to use the smaller resistors. 

    They can also put a feedforward capacitor in the range 10nF ~ 100nF from OUT to FB to further improve noise and transient performance, as well as PSRR.

    Regards,

    Nick