HIP4082 input & bootstrap problem

Question

Concerning the HIP4082 IC from intersil. I was asking about the input to the IC. Pins (ALI,BLI), can I use a very low frequency input on these pins for example to control a stepper motor, so the frequency won't be stable sometimes up to 1 KHZ and other times as low as 1 HZ or even slower.
The problem is how will the bootstrap capacitor be charged ?

Answer 1

You're right to be concerned with how the bootstrap capacitor will be charged at low frequency. Bootstrap N-channel gate drivers (like HIP4082) have a known drawback that they can't operate at 100% duty cycle, because the bootstrap capacitor discharges over time. Similar thing can happen if the frequency is very low.

You could use a large bootstrap capacitor. If your application allows it, you could short off-periods when the gate is low - just to recharge the bootstrap capacitor.

I have ran a bootstrap circuit** at 60Hz. The capacitor discharge wasn't a concern. i would imagine that you could use a bootstrap gate driver at 1Hz.

** That was a bootstrap gate driver made with discrete components. It wasn't a HIP4082. YMMV.

By the way, this app note can come handy.