I'm copying “Ultra-Wide Input Range Non-Isolated 12V Buck Converter” from LT8316 datasheet into LTspice. But the results seems to be very strange. The voltage on FB is even higher than Vin, which is way above the standard reference voltage(1.22V). I can't find any difference between the datasheet and my LTspice project, all the diodes are confirmed. Can somebody help?

 

voltage on FB is even higher than Vin, which is way above the standard reference voltage(1.22V).

I think you are measuring "FB" by looking from Ground to FB. The voltage on FB is AC and can be as high as Vin + a small amount to as low as about Ground.
When you look at the pins on the IC you need to look at the voltage from "gnd" to "fb". Do you know how to do that in LTSPICE?


Key point is that the IC is not sitting on Ground! It is sitting on a point that is switching from Vin to Ground.

 

The voltage on FB is even higher than Vin

As noted, you need to measure between FB and the IC GND.
You do that by clicking on the FB node, and then without releasing the mouse button, go the the GND node and release the button.

My simulation of the circuit shows it cutting out after a few ms since your Rload1 value of 10 ohms gives too large an output current.
The data sheet says the maximum load is 200mA giving a minimum Rload1 of 60 ohms.

 

Thank you guys! Very specific and clear answers!

 

I'm copying “Ultra-Wide Input Range Non-Isolated 12V Buck Converter” from LT8316 datasheet into LTspice. But the results seems to be very strange. The voltage on FB is even higher than Vin, which is way above the standard reference voltage(1.22V). I can't find any difference between the datasheet and my LTspice project, all the diodes are confirmed. Can somebody help?

There were a couple of minor errors on your schematic, but the biggest issue was likely that you must look at the difference between the FB pin and the GND pin on the part since the GND pin is not connected to circuit GND.

I changed the output capacitor to be 3x 47 uf with 10m ESR, and the load resistor to 12 V/100 mA = 120 R rather than the 10 R load you had. I also added some net labels to the fb, zero (i.e. the LT8316 GND pin), and the output node to make probing easier. I shortened the run time to 200 ms. I have attached my modified schematic and plot files.

If you zoom into the waveform at the end of the run you will see the FB voltage (i.e. the voltage V(fb, zero) the voltage between the fb and zero nets) is about 1.3 V during the off time and about -0.7 V during the on time.

HTH

 

There were a couple of minor errors on your schematic, but the biggest issue was likely that you must look at the difference between the FB pin and the GND pin on the part since the GND pin is not connected to circuit GND.

I changed the output capacitor to be 3x 47 uf with 10m ESR, and the load resistor to 12 V/100 mA = 120 R rather than the 10 R load you had. I also added some net labels to the fb, zero (i.e. the LT8316 GND pin), and the output node to make probing easier. I shortened the run time to 200 ms. I have attached my modified schematic and plot files.

If you zoom into the waveform at the end of the run you will see the FB voltage (i.e. the voltage V(fb, zero) the voltage between the fb and zero nets) is about 1.3 V during the off time and about -0.7 V during the on time.

HTH

Thank you for giving suggestions!