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TPS766xx LDO Output Capacitance

The TPS766xx data sheet includes some typos concerning output capacitance. Please reitterate the Cout requirements and in particular comment on the ESR requirement for larger capacitors. It appears from the data sheet curves that the requirement is really that the ESR zero be less than 320KHz. Is this correct?

Incorrect wording from data sheet: "The minimum recommended capacitance value is 4.7 mF and the ESR (equivalent series resistance) must be between 300 mW and 20 Ω."

My customer would like to use a 100uF, .022 ohm cap. This would place the ESR zero at 72KHz, which I believe should be OK.

  • You are correct in that the minimum ESR for Co=4.7uF needs to be 300mOhm not 300mW.   That ESR range only applies to Co=4.7uF.  In general, the ESR minimum lowers as the output capacitance increases.  The exact value for the ESR zero depends on what is generating the dominant pole in the system, the output capacitance or the internal error amplifier.  As the output capacitor increases, the pole it creates gets lower in frequency and can approach the error amplifier pole.  Your customer's value ESR sounds reasonable for that Co but I suggest they check the ringing after a load transient in-system if possible just to make sure.  In some cases, significant additional ceramic capacitance in parallel with the bulk Cout can cause instability.