Original question:
Tool/software:
Hi,
We are concerned about poor PSRR at 1MHz and I am trying to simulate PSRR with PSpice, I am new to this tool and need guidance.
How would I go about accomplishing this ? I have found examples with LTSPICE that I am using as reference, but now sure how to measure ripple at input and output and feed that back into a transfer function that is sweeped over frequency.
Thanks
Hi Daniel,
1MHz is outside of the LDO bandwidth (which is usually something like 200kHz at full load for LDOs), so the PSRR at that frequency is only due to the output capacitor - the peak in the PSRR plot is due to the same. So, to increase the PSRR at 1MHz, you would need to get the output capacitor impedance at 1MHz down, and the easiest way to accomplish this is to choose a capacitor that resonates at 1MHz, and using multiple of the chosen capacitor will improve the effect. I'm trying to work out how to simulate the expected PSRR with this method, but I'm getting an answer that doesn't align with my expectation. I'll update you if I can figure out a good way to simulate it.
Regards,
Nick
