Isolation between DCDC input and other loads or other DCDCs in Parallel

[OneGeekGuy]

Hi all!,

I am currently designing an Evaluation board to do some testing with an ESP32 and some solenoids. In this case I am using a DCDC Buck converter to get 5V from the 12V Input which will be supplying the ESP32. On the same 12V rail, there are solenoids connected, not big deal just miniature solenoids (0.2A@12V). I was taking a look to placing two 10uF Electrolytic caps close to each Solenoid control circuit (NMOS) in a way I can reduce the effect on the 12V line due to the solenoid switching (Low speed, do not expected high speed switching on the solenoids).

My question was, and maybe it is a bit overthinking if the extra 20uF capacitors would affect the dynamic behavior/stability of the DCDC converter, how this could be isolated, using LC or Pi filter to adapt or isolate the Input impedance on the DCDC converter? How use to be done in situations in which the need of adding a lot of capacitors on other branches connected to the same rail as the DCDC might significantly affect the Input impedance on the DCDC?

Also, one thing to consider, the Electrolytic caps will approx. 20mm away from the DCDC input in which close to it will be the real Input capacitors for the DCDC (x2 10uF MLCC)

Thanks in advance for any comment or feedback.

[edavid]

Yes, you are overthinking.  Don't worry about it.

Also, why did you choose to place 20uF at each solenoid?  I wouldn't think that would be enough to make a difference.  I would start with 470uF.

[langwadt]

Yes, you are overthinking.  Don't worry about it.

Also, why did you choose to place 20uF at each solenoid?  I wouldn't think that would be enough to make a difference.  I would start with 470uF.

or place it a the input at the DCDC making 5V with that diode in series with the 12V supply, that  way it'll power the DCDC through any small dips in the 12V

[PGPG]

if the extra 20uF capacitors would affect the dynamic behavior/stability of the DCDC converter

Have you ever read in any appnote that adding extra capacitance at DCDC input can ruin its stability?
At DC 12V supply I would rather see 220uF or 470uF capacitors.

[OneGeekGuy]

Yes, you are overthinking.  Don't worry about it.

Also, why did you choose to place 20uF at each solenoid?  I wouldn't think that would be enough to make a difference.  I would start with 470uF.

It was eyeballed, I need to check the specs of the Solenoid and make some calculations, as you stated probably 20uF is useless, also 470uF might be challenging to fit within the size of the PCB, but I can still figure it out.

or place it a the input at the DCDC making 5V with that diode in series with the 12V supply, that  way it'll power the DCDC through any small dips in the 12V

Is my understanding correct, you are suggesting to "isolate" the DCDC generating 5V using a diode in series so no current will flow back from the DCDC bulk input caps?

if the extra 20uF capacitors would affect the dynamic behavior/stability of the DCDC converter

Have you ever read in any appnote that adding extra capacitance at DCDC input can ruin its stability?
At DC 12V supply I would rather see 220uF or 470uF capacitors.

That is a good question, I think I got confused with adding an Input Filter to the DCDC, I do not remember having extra input capacitance affecting the DCDC. So maybe the question should be focused on trying to avoid loading the Solenoids from the Bulk capacitance on the DCDC regulator, if this could even happend with that small Solenoids.

Thanks!!

[langwadt]

or place it a the input at the DCDC making 5V with that diode in series with the 12V supply, that  way it'll power the DCDC through any small dips in the 12V

Is my understanding correct, you are suggesting to "isolate" the DCDC generating 5V using a diode in series so no current will flow back from the DCDC bulk input caps?

yes