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How to evaluate PSRR of an LDO?

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Newbie level 5
Jul 11, 2011
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Hi guys,

Can any one help me how to measure PSRR of an LDO and what measuring instrument to use in order to measure PSRR?
would it be okay if i embedd a sinusoidal signal on top of my Supply Voltage and measure the RMS value at the VCC line and at the OUTPUT line?

thanks for these references. but i want to know how to do it during bench test? i was thinking of doing it by like that of simulation however i dont know what instrument to use to measure the ripple at the output. so im thinking i just have to use a multimeter set at Vac fucntion and measure the ac ripple at the input and the ac ripple at the output and just solve the dB equivalent?

You can measure LDO PSRR using a network analyzer and a power amplifier. An oscilloscope with a function generator and amplifier might also work as described in the article.
To measure AC PSRR of LDO, you can use LC summing node or a bias tee. This mixes the AC and the DC of your signal generator and DC power supply. When using a bias tee be sure to use high current driving capability..picosecond 5547 can do the trick if your ldo load is less than 500mA. Then you can measure the Input ripple which is supplying by your signal generator at a defined ampitude(lets say 500mV ptp)and frequency and measure its corresponding ripple across the input and output capacitor with a spectrum analyzer. The logarithmic ratio of output to input is your PSRR.

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