We are using the MP3431 to supply the voltage for an Hbridge which is driving a purely resistive load of ~9 ohms at 25 kHz. The input voltage is a battery pack with a nominal voltage of 10.8V and and output voltage of 14V. Here is the circuit we’ve built on our first prototype PCB:
It is based off this MPS target design:
We are seeing large drops in the output voltage when the load is switched on, roughly ~2.8V of variation. This is causing problems since we are trying to precisely control the amount of power delivered to the load. Here is a scope capture showing the step response:
OUT2 is the voltage across the 9 ohm load.
Is this just beyond the capability of the MP3431 to handle a step response like this?
Are there any design issues with the circuit?
Is there anything we should try with the compensation network to improve the step response?
We are very space constrained and had to compromise on the amount of output capacitance so we are expecting less than ideal output voltage ripple but even this is far beyond the estimate from the web design tool. Any help is appreciated, thanks!