Why does the SW point of the LM2842 have a phenomenon as shown when the inductance of LM2842 is insufficient, and when a large inductance is changed, a normal square wave is output?
What is the specific reason?
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Why does the SW point of the LM2842 have a phenomenon as shown when the inductance of LM2842 is insufficient, and when a large inductance is changed, a normal square wave is output?
What is the specific reason?
HI
the attached waveform is abnormal, it may due to small inductor caused the sub harmonic oscillation. you can use wenbench design tools for the schematic design for choosing proper output inductor and capacitor.
Is this because the inductance is too small and the energy storage is insufficient to enter the DCM mode?
Hi
I see you raise up same question on https://e2e.ti.com/support/power-management/f/196/t/938114
cause the inductor and output capacitor value will affect the loop stability of whole DCDC converter. I think you may have small value of capacitor too. our EVM is also 15uH, with 2*47uF 6.3V ceramic cap.
Thanks
Daniel Li
So in the design, it is not the DCM mode, is it? If in other circuit designs, if the inductance value is small, will it also enter the DCM mode?
Hi
In stable statues, the Device will come to DCM mode when Io<0.5*Iac(ripple current), and it will still be stable. smaller inductor will have larger ripple. It means the load current in DCM mode will higher then larger inductor case. so even you use larger inductor, there is still be a load current the device will come to DCM mode.
Thanks
So what I am wondering is whether the current is not enough because my inductance is too small and then the SW point oscillates when I enter the DCM mode. Or is it because the inductance is too small to cause stability problems
Hi
I think it is stability issue , our EVM is also 15uH inductor.
Thanks