Other Parts Discussed in Thread: LM5122
Hi
I have built a high current 12 volt to 14.5 volt interleaved booster that has problems with the slave output and top fet not operating as per the datasheet
I have .0025 ohm resistors in the sense on both master and slave
Although both sides are drawing the same current the master top fet (synchronous rectifier) is operating correctly but the slave doesnt receive full gate voltage until > 30mV is developed across the sense resistor (data sheet indicates > 7mv). All indicated on a calibrated CRO
I have changed the slave LM5122 and the problem still exists. I have rebuilt the circuit on another PCB but the problem still exists
If the circuit is run at max output, with a higher voltage drop across the slave sense resistor the top fet operates correctly, but if the output current is reduced the fet gate drive is reduced (wave shape is still square but now has a step) and the slave top fet becomes HOT (as you would expect)
I am using PSMN4R5 fets that have a min turn on gate voltage of 2v and a max of 4v. This however does not explain the wave shape change
The interleaved circuit I have built is similar to the datasheet and values derived from WEBENCH
Any help would be greatly appreciated
Regards
Alan
