Hi Sir,
My customer design TPS7A2018P and feedback the output voltage has spike if there is inrush current.
Other vendor’s solution waveform is ok.
Would you please review this case and provide your comment?
Here are schematic, block diagram and environment setup.
BR,
SHH
Hi SHH,
I tested an EVM and I'm not seeing the same thing that the customer is seeing. The EVM that I have is using plenty of Cin to hold this steady, and Cout is 2x 2.2uF capacitors. I do not think this is due to Cout but I believe the issue is on the input. I think the small spike on Vin in the customer data set is causing the issue. It could be that the LDO is falling into dropout during turn on, which is causing this overshoot. Another option is ringing on Vin during turn on, caused by the ferrite bead or stray inductance, which is interacting with the LDO. To mitigate this you could remove the ferrite bead, or increase Cin. You should have the customer provide a zoomed in plot of the test data, at 0.1 ms / division, to see where Vin drops during turn on and what is going on.
Here is a link to an App note describing the issue (overshoot during turn on caused by the LDO being in dropout).
Channel 1 = Vin
Channel 2 = EN
Channel 3 = Vout
Channel 4 = Input Current (I was not able to quickly break the connection on Vout to easily measure Iout, but I think the issue is on the input so this shouldn't matter)
Thanks,
Stephen
