LTspice sim is not regulating

[Faringdon]

Hi,
Why is this LTspice sim not regulating...its an attempt to regulate the output current.
Top FET getting turned on continuously.....a bootstrap driver cant do 100% duty , so why does it try to?

[Andy Watson]

If I've read your circuit correctly, you've created a positive feedback loop. U3 increases output with increasing current. U2 inverts this - so its output reduces as the current increases and it appears that you are feeding this "voltage" back to the switcher, U1 - which presummably (I've not read the data sheet) sees this as a lack of output voltage - so it increases its output - as far as it can.