Ok, I have some actual oscilloscope measurements now. PWM frequency is 25KHz and measures correctly now. Apparently I was doing something wrong on my ESP32 when it seemed to be doubled.
Battery 7.7v
100% duty:
Low side gate 0v
High side gate 6v
Bootstrap capacitor 3.5v
Mosfet output 6.4v
2/3 duty:
Low side gate alternates 0v and 8v
High side gate alternates 0v and 7v
Bootstrap capacitor is mostly 7v, with 230ns blips up to 10v
Mosfet output is mostly 0v with 230ns blips up to 3.4v
1/3 duty:
Low side gate alternates 0v and 8v
High side gate alternates 0v and 7v
Bootstrap capacitor is mostly 7v, with 230ns blips up to 13v
Mosfet output is mostly 0v with 230ns blips up to 6.2v
The blips seem to occur during the deadtime window, starting as the high side gate is switched off, and ending just before the low side gate is switched on.
For comparison, I took the same measurements on Lepton:
Low gate alternates 0v and 8v
High gate alternates 0v and 15.5v
Bootstrap capacitor alternates 7.4v and 15.2v
Mosfet output alternates 0 and 7.7V, with small spikes at the transitions to about 8v and -0.3v.
So apparently the bootstrap is not working, but I still don’t know why.