Hello,
I designed a buck-boost using LM34936-Q1. I am noticing that the output ripple has weird shape ( attached).
I measured SW jitter, Bode plot. Everything is fine. Jitter less than 3% and Phase margin > 80 degree, BW = 25kHz for FSW = 400kHz.
The noise is periodic.
VIN = 16V, VOUT = 10.7V, FSW = 400kHz. I checked SW node, only buck side is switching.
Hi Feng,
I checked SW2 it is steady. Please see the waveforms below.
First is SW1 and VOUT
2nd is VOUT and voltage cross current sense ( Inverted) . I am using 3 mohm current sense. Please see the values in the schematic snapshot
Hi Feng,
Below waveform is at 4A IOUT, VIN = 14V, VOUT = 10.7V. Yellow: VOUT, GReen : CS-CSG inverted.
To me, current sense looks okay. I was thinking may be a case of insufficient slope compensation, so I increased the C_SLOPE from 100pF to 120pF. The recommended from excel tool is 120pF. But no effect.
Hi Ajit,
The duty cycle is stable from the first waveform.
And it seems there is also periodic noise from Vcs waveforms. Do you think the periodic noise might come from test setup? Where do you put the ground wire of the probe?
Best Regards,
Feng Ji
