In a flybuck application, the isolated output power rate may be limited by the low-side sink current limit. Therefore, users must select design parameters elaborately to promote the isolated power rate. The key factors affecting the negative primary winding peak current are D_max, N₂/N₁, N₃/N₁, and the output current. The following tips are for trying to keep the margin:

1. Select a reasonable range of duty cycle. TI recommends a duty cycle ranging from 20% to 50% in most cases. Users can reduce D_max by setting a lower primary voltage or increasing the minimum input voltage to increase the negative current margin.
2. Minimize the leakage inductance. Leakage inductance is a crucial factor determining the ramp rate of the current in the secondary winding which charges the output capacitor. A nominal amount of leakage is within 1% of primary inductance.
3. Pick the correct turns ratio. A lower turns ratio (isolated side to non-isolated side) results in a lower reflected current in the primary winding.
4. Raise the non-isolated output power, which will reduce the negative winding peak current.
5. Reduce the isolated output power. This is the most direct way to lower the level of the negative current.