Do

• Use multiple resistors for the high voltage startup resistor network
• Limit the current into the FLT pin, as the pin can only handle 5mA
• Use multiple resistors for the current sensing resistor if designing for higher power designs (such as 60W)
• Use high frequency bypass capacitors close to the transformer in addition to the bulk capacitors
• Place the slope compensation resistor close to the UCC28750 device, not the current sensing resistor
• Use an additional current sensing filter capacitor to aid the leading edge blanking with noise filtering
• Place a resistor in series with the DRV pin to the gate of the MOSFET to tune the turn-on and turn-off rate of the MOSFET
  • To increase turn off speed, use a separate diode and resistor path for the turn-off edge to have a faster turn-off edge and a slower turn-on edge

Figure 8-18 DRV gate drive resistor network setup

• Use small traces for the power path, use large traces, greater than 40mil (1mm)
  • A trace can carry about 0.5A to 1A per 10mil (0.254mm) trace thickness
• Put high voltage traces next to low voltage traces, use a high voltage spacing rule and set a restriction in layout
• Arbitrarily place grounding points, have a particular power path ground loop and a separate signal ground loop, tied together near the power stage input bulk capacitor