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Selecting capacitors to use with LDO regulators

andre.robotokogaku
Intellectual 440 points
Other Parts Discussed in Thread: TPS7A80

Hello guys,

I'm planning to use the TL760M33 3.3 LDO voltage regulator and I'm concerned about the stability of the IC with respect to the output capacitor ESR. Datasheet says the ESR should be between 1.4 and 2 Ohm.

The thing is that I'm using, in the 3.3V power bus, some low ESR caps to filter EMI. Will theses caps destabilize the LDO, even if they are not close to it? If so, how can I solve the problem?

 

Thanks in advance,


André.

  • 0
    TI__Expert 8890 points

    Hello Andre,

    Yes, it is always a fear that the down-line bypass capacitances can destabilize the power supply - and this is true for any power supply including this regulator.  Typically however if you use say a 10uF tantalum cap with approx 1.5ohms esr (TPSA or TPSR*106*006 from AVX) , this amount of capacitance swamps any effect from the bypass capacitance down-line. Only if the other filter capacitances add to the same order of magnitude as the output capacitance will you have a possible problem.  But then you can increase the output capacitance ( from 10uF to 22uF) to compensate for the other added filter capacitors.  And increasing the output capacitance will have the added effect of allowing lower esr. Roughly doubling capacitance allows halving esr (though this is not characterized on the data sheet and therefore not guaranteed).  

    Please also note that the esr is a function of load - according to the data sheet Fig 1. If you artificially added a 30mA minimum load you could also steer away from your esr dilemma.  

    I might also recommend using the TPS7A80 in your application.

    Bill

  • 0 in reply to Bill Stokes
    Intellectual 440 points

    Thanks for the quick and precise answer, Bill!

     

    André.