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Original question:

tps737: I can't understand 8.2.2.1 section of TPS737 datasheet

TPS737: Output capacitor selection

Yusuke Mukuno
Expert 7395 points
Part Number: TPS737

Hi Expert,

My customer is considering about output capacitor with TPS73733.

In generally, The 1uF MLCC has around 10mohm ESR.

Cout x ESR = 10(nF x ohm)  , It is below 50nF x ohm.

Is it meaning, we cannot use ceramic capacitor? or The total ESR is more higher, because it should have parasitic resistance,  board, socket, and solder joint resistance, something like that.

How should we think about it? please give me your advice.

(Datasheet description)

The TPS737xx requires a 1-μF output capacitor for stability. It is designed to be stable for all available types and values of capacitors. In applications where multiple low-ESR capacitors are in parallel, ringing may occur when the product of COUT and total ESR drops below 50 nF. Total ESR includes all parasitic resistances, including capacitor ESR and board, socket, and solder joint resistance. In most applications, the sum of capacitor ESR and trace resistance meets this requirement.

Thanks

Muk

  • 0
    TI__Mastermind 29150 points

    Hello Muk,

    The datasheet specifies that the capacitor and series resistance must not fall below 50 n-ohms.  For a 1uF capacitor this equates to 50 miliohms of parasitic resistance.  A ceramic can be used if the total combination of parasitic resistances (board resistance, contact resistance, and internal ESR of the capacitor) add up to greater than 50 miliohms.  Having said this, we recommend the output capacitor to be very close to the linear regulator output to reduce parasitic inductance.  If this guidance is followed it will be difficult to meet the 50 miliohm resistance requirement.  You may wish to add a small series resistor in series with the output capacitor if this is the case.  A 50 miliohm series resistor would meet this requirement for a 1uF ceramic output capacitor.

    Thanks,

    - Stephen