I've started a power design using TI's WEBBENCH. The resulting design utilizes a LM22678-Q1 (-5V). The output plots show under 3mV of ripple, which is acceptable. However, I don't know if this is assuming 0V ripple on the input supply. The data sheet doesn't have any PSRR specs on it, so I'm at a loss on what to expect if there is any noise on the input supply voltage.