control issues with LM5160QPWPQ1

Hi

For Synchronous Buck / Fly-Buck P/N LM5160QPWPQ1 we have control problems. Initial circuit is according to the below circuit.

Spec:

• Vin=15-21V. all tests was performed in 18V
• Po max=5.5W
• Transformer ratio 6:28. Primary inductance 12uH. Leakage inductance 1.5%
• Switching frequency=300kHz
• Buck regulated voltage: 5V, and load of the 5V is 1W
• 3 output isolated voltages 23V with nominal 1W load each. Maximum 1.3W each

We have control issues with it. We are trying to work according the data sheet in 300kHz, but the controller is not stabilizing the output voltage.

In the data sheet page 22 there is a recommendation below, but it didn’t work when we put it:

We need to understand what is the problem and how can we fix it?

thanks,

Lior