Hi,
We have a design using an LP87524J PMIC providing 4 voltage rails from a 5V supply voltage as shown in the schematic below.
We are setting the output voltages and startup sequencing at power on through the I2C interface.
I am seeing some noise on some of our boards on the 2.2V output which occasionally causes the PWR_GOOD to assert low and reset our system. I have read the registers when this happens and it is always the Buck 2 regulator that is causing the issue.
The following 2 captures show the output of Buck 2 across C135 on a board which is showing this issue, the persistence display shows that the sinusoidal waveform varies with time quite a bit:
The next scope capture is a different board that is not exhibiting this issue:
On the board showing the issue I also took measurements on the downstream side of the ferrite bead and I still see some of the sinusoidal noise but with a lot of the higher frequency components filtered out.
Are there load conditions that would cause the PMIC to respond in this way? We have done the layout according to the recommendations in the datasheet.
Thanks,
Kevin
