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UC2843: Floating Buck converter, System stability issues

Part Number: UC2843

I am designing a Floating Buck converter(Power Switch connected in negative DC input side, positive rail directly connected to the battery) for 52V/15A Battery Charger using UC2843, Battery Should charge at 15A in CC Mode until the battery voltage reaches around 51V. 

Based on the application note given here  https://www.ti.com/lit/ug/tidu413a/tidu413a.pdf?ts=1606830361321&ref_url=https%253A%252F%252Fwww.google.com%252F 

The inductor current is not constant when the duty ratio is above 0.5.  the slop compensation designed based on the UC2843 datasheet. please help me out solving the problem.

  • the circuit diagram and Inductor current, Switch current and Gate pulse waveform given here, please help me to find and correct the problem

  • Hi Ramesh,

    The first thing you should check is your IF opto current because at least on the time scale provided it appears to be ~0 mA which means that neither your CA or VA is sinking current. The opto is rated for IFmax=30 mA so you can reduce the 1 kΩ resistor in series with the opto diode. Verify the CA and VA are operating with the dynamic range you expect so sufficient current is flowing through the opto. Check this for CC, CV and especially within the transition between CC/CV boundary. Once you are satisfied the control amps are biased and gain is correct, try increasing the amount of slope comp and see if the instability is removed?

    Regards,

    Steve M