a ring oscillator used to control a charge pump (it takes a couple of µs to swing on).
A boost circuit (two diodes an resistor and 1 capacitor) is used to get better control over the FET bridge, by changing the potential a bit.
After the first few seconds the lowside FET operating point will pulled down by the charge pump to ensure the FET close fully.
additionally to that, one could add an delay circuit.
