Hello,
I am working on creating a device which uses an esp32 chip to measure temperature and humidity and adjusts the speed of two fans depending on these measurements.
For this I need a 3.3V power supply for the esp and the sensors and a 12V power supply to power the fans. The input voltage is 230V mains power that I have rectified to DC.
I am trying to achieve this using two mp9488 in parallel. The one for 12V seems to work as inteded, but the one for 3.3V pulses on about two times a second.
A picture of the 3.3V circuit should be attached here
Do you have any ideas what might be causing this behaviour and how to fix it?
Thank you in advance, Jonathan.
Hello @JLundhoj ,
About how much current do the fans pull from the MP9488?
Kindly provide Vout, switch node voltage and, inductor current waveforms. By seeing these three waveforms I can get a better idea of what is happening and how to best help.
Regards,
Jonathan
Mightn’t you be better off deriving the 3.3V from the 12V? 3.3 from 300 is a pain and this kind of sampled feedback circuit is touchy.
You are probably in trouble with the leading edge blanking. The first 400nsec after the switch turns on the current sense amp is blanked. But with 300V in and 100uH of inductance the current is going to be at about 1.2A as soon as the current sense amp takes a look At that point it looks like the system will think it is shorted and shut down for a bit. The reference circuits in the datasheet use 1.2mH inductors.
