Half Bridge Driver IC Usage inquiry

Question

I want to use this Half Bridge Driver for a Buck converter Design. To validate it, I wire the connection as the simplified application diagram in the datasheet, with .1 uF capacitors. The input VDD is 12V. I feed the High and Low inputs with a %50 percent fixed duty cycle at a 15KHz frequency using a micro-controller as shown below on the Left. There was a small dead-band included for protection.

I expect the output at HO and LO without anything connected to be a square wave but I receive the output below on the right, where green is the low side, and yellow is the high side:

What did I do wrong? What Can I check? When I turn the driver on without input I see a biased Voltage around 10V.

Answer 1

I expect the output at HO and LO without anything connected to be a square wave

Don't.

The MOSFETS need to be connected to see an output square wave? ... Do I also need to connect the inductor and capacitor?

Of course! High side MOSFET needs a gate voltage higher than its source voltage to turn on. As can be seen from the schematic below, the voltage on its source is approximately the output voltage and CBS is used for "adding" this output voltage to the gate. That's called bootstrapping.

Here's how a bootstrapped driver is used in a sync-buck converter:

^{simulate this circuit – Schematic created using CircuitLab}

NOTE: I didn't show the external diode because UCC27201 has it internally.