I'm currently using a LM5109B to attempt to drive a high-side N channel mosfet in a particular setup. I want to drive it independently of the low-side driver. I'm aware that the provided IC is used for H-bridge configuration. As expected, when there is no load and HI is pulled low, the HS is floating and the gate is driving. When I put a load with HI low, the gate doesn't drive. Is there any solution to ensure that HS isn't floating in this particular situation? Is there any High-side gate driver that can be used for this particular application? 
Thanks
Electronic – Driving a high-side N-channel FET
mosfet-driver
Related Solutions
Yes, the 1K gate-to-source resistor is creating your problem. The good news is, you don't need it. A gate-to-source resistor is needed if your MOSFET cannot be actively driven off when it is needed to be, but that is not the case with the IR2101. You will often see a gate-to-source resistor used when a MOSFET gate is connected to a microcontroller to force the MOSFET off until the microcontroller can initialize the pin as an output.
Here is the datasheet for IR2101. And here is the Functional Block Diagram (from the datasheet):
As you can see from the functional block diagram, the gate drive outputs HO and LO are actively driven both high and low so the 1K ohm resistor is not needed.
The problem that you are seeing is that the bootstrap capacitor is being discharged through the 1K ohm resistor (in series with the 100 ohm resistor). From looking at the decay rate on your waveform, it looks as though that waveform was captured with only the 330nF capacitor in place (using the formula T=RC to get the time-constant).
Yes. Any form of isolated or boost supply can provide the high-side gate voltage referenced to its source. Some ideas:
- Floating Charge pump (I was considering the LTC1754 for a very similar application)
- Small flyback with output referenced to source
- Floating boost
- Photovoltaic cells powered by on-board LEDs (Photovoltaic Isolator)
The main concern is level-shifting the control signal without killing your deadtime, introducing too much latency, or slowing down turn-on.
Obviously you need to be cautious of exceeding the Vgs during turn on/off of the floating supply also.
Some references:
http://www.vishay.com/docs/91421/appnote9.pdf
Is it safe to "top up" bootstrap capacitors using a charge pump?
http://www.ti.com/lit/an/slva444/slva444.pdf
https://www.fairchildsemi.com/application-notes/AN/AN-6076.pdf
Best Answer
That chip uses bootstrapping and, bootstrapping requires that the load voltage goes high and low quite frequently. If this does not happen then the bootstrap capacitor loses its charge and you will be unable to drive the HO pin above the level of voltage on the source of the upper MOSFET. And, that means you can no longer activate the high-side MOSFET.
If you want a solution you should use an isolating DC-DC converter that can apply a voltage higher than Vin to the upper driver circuit.