Hi Team, I am assisting a customer seeking for your inputs.
Trying to create a 9 V to 3.3 V buck converter using the Lm2650 chip. I used the circuit topology shown in Figure 18 along with the components in Table 1 to prototype with the chip. I left the Freq adj pin unconnected, as I believed that is how you would get a switching frequency of 90 kHz.
One big issue I had with this circuit was getting a consistent output voltage. I found that when I put different resistors from Vout to ground, it would change what the output voltage is. I tried putting a very low resistance to get a larger output current (as that is what Table 1 is rated for), and found that ~25 ohm load would get a 3.1 V output.
Trying to make a consistent power supply for a fluctuating load circuit, and seeing small differences in load resistance changing the output voltage worries me a lot. I was hoping that this chip would provide a consistent output voltage through hysteresis/PID control, but it does not seem to be doing that.
Is there something that I can do in order to bias this circuit correctly at the right output voltage? Could I be making some type of wiring mistake, or could it be that a different IC would have better results at maintaining a consistent output voltage with a varying load?
Thank you.
-Mark
