I have a UCC1806 that skips pulses at less than 20% of max load. Typically they go down to 10% of max load. This one has an unusually large output inductor which should extend the min current lower. When it skips a pulse pair the output inductor goes discontinuous and causes spikes and high ripple on the 5 V output.
Here are the parameters of the suppply.
1) push pull topology typical hookup with no current slope compensation. 2) 44(ct):24(ct) transformer 3) Input 30V : output 5V @ 4A max 4) Output inductor: 100uH, low esr electrolytics at 400uF on the output 5) current sense transformer 1:75 with 37 ohm burden resistor and a 499 ohm with 100pF spike filter before the isense pin. 6) Ilimit pin is set to 5.6V though some 200K range voltage divider from a 10V reference (forget the exact values) and is decoupled with 2uF. 7) SD pin is tied low. 8) Sync and from a crystal osciliator and the Rt is tied to vref and Ct is ground (external clock operation). 9) switching Freq is 100KHzIs there any indication from the above that could cause a problem. @800mA output current the current ramp is about .25V and clean. Then all of a suddend evey other pulse pair stops occurng reliably. raise the output curent to 1 amp and above and the supply acts normally.
any ideas on where to look?.