Load step regulation of MP9486

DC-DC Power Converters
1

Hi,

I am using an MPS9486AGN-Z to convert Vin (20-30V) to 5V, 1.2A output but the load step response is very slow. The output recovery time is about 500ms. The design is based on the typical application in the datasheet but the inductor is 47uH and the output capacitance is much larger (100uF on the output plus 820uF+1000uF further downstream with a ferrite bead in series, between 100uF and the two larger capacitors). The load step is 0.2→1.2A and the voltage drop is about 8mV at the 100uF capacitor and about 24mV at the 820+1000uF capacitors. Why is the regulation so slow, can it be improved? Fsw is about 277kHz.

2

Hello,

Generally, I would recommend using a higher switching frequency as this would mean you would have significantly faster voltage transitions. The MP9486A is capable of switching up to 1MHz. Try stepping up by gaps of 100kHz to test the regulation time performance.

Having excessive output capacitance can also be a factor in a slowed regulation time. I would recommend using the configuration as seen in the typical application:

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3

Of course, when you increase the switching frequency and decrease the Cout, be wary of the output ripple. This is the primary tradeoff in changing these features.

Best,

Krishan