Hello.
Need to create DCDC for 12V/7.5V output with the MPQ4372 automotive device.
In addition to the ceramic capacitors for stability, I need to add large aluminum polymer capacitors to absorb the back EMF.
Is there a limit for Cout[max] and if so, what is it?
Thanx,
Eli.
Hello Eli,
The datasheet offers the following insight on the output capacitance:
There isn’t exactly a metric for the maximum capacitance for the output stated explicitly in the datasheet. What is the total capacitance that you have being used? Have you tested the MPQ4372 with this output capacitance? What is your expected load current?
Best,
Krishan
Hi, Krishan.
I am not yet sure about the maximum output capacitance required.
The motors combined draw about 6A, but the back EMF depends on the control loop as well. I would be glad if it’s possible to add a 1000uF aluminum electrolytic capacitor to absorb an 800mA low-frequency ripple under certain conditions.
I would recommend that you test this on your current config or with an EVB when you get the chance.
If the output capacitance is excessive, then this may destabilize the buck stage if you are not able to compensate the controller aspects to maintain stability. From a controls standpoint to explain why excessive capacitance affects the loop stability, the phase margin and loop bandwidth decreases. Otherwise, your ripple and low-frequency stability will surely benefit.
If you have the space to accommodate this, you can try adding a filtering inductor or perhaps a choke before the extra-large aluminum electrolytic capacitance as opposed to being in parallel with the typical ceramic capacitors.
This architecture should prevent this extra capacitance from affecting the control loop of the MPQ4372.
