despite the analysis tools saying that the phase margin is around 90 degrees, the device is inherently instable, oscillating at 7khz. input 5V out 2.4V low current around 100mA. external sync at 847.5khz. goal minimal ripple/noise.
Hi,
Are you doing the hardware testing right now? Can I see your set up and the Vsw waveform?
Best,
Fox
I turned on persistence to see the switching spread and oscillation. green below the classD stage RF field at 6.78Mhz, and the switching at 6.78/8=847.5kHz, MP1496S feeds the classD stage at 2.4V ; load is constant. Isupply is 40mA at 5V; 10 ohms, 220nF extra filter between MP and classD load.
I use an external voltage source with 82k into the fb pin to set the output voltage. unfortunately one cannot simulate this with the online or offline simulator.
sometimes the chip switches to discontinuous mode, looking apparently more stable.
what makes the chip behave like this ? it is externally synchronized to 847.5kHz.
I give up. This chip cannot be tamed, and is also quite brittle, easy to destroy.
time to move on to another brand.