UCC23513: UCC23513 working on 200kHz switching frequency for LLC

Hi Gary,

The UCC23513 can switch at almost 25MHz unloaded.

The package has a power rating of 0.75W, operating junction temperature of 150C and a Theta JA of 126°C/W, which means that if the ambient temperature is 125°C, UCC23513 can cycle a 1nF capacitor load at 18V at 600kHz before its thermal rating is exceeded at this temperature extreme. 

(150-125)/126 = 0.2W

CV^2 = (1nF) * (18V)^2 = 324nW

f_sw = 0.2/ 324n = 612kHz

However, it is usually more important to determine the switching losses of the Mosfet. This will vary based on the gate driver's output drive strength and the externally added Rg and Cgs. If the switching losses are too high, the Mosfet will burn up at a much lower frequency than the gate driver. 

For example, C3M0015065D is a SiC FET with a nominal 1.5mJ turn-on and a 0.7mJ turn off. However, this will change based on externally added Rg and Cgs. 

The UCC23513 has a pretty good output drive strength compared to competitors, and it can help to improve switching efficiency of mosfets and enable higher switching frequencies. In the measurements below, you can see the UCC23525 can provide higher output drive strength when the externally added Rg is less than 12 Ohms:

C3M0015065D with UCC23513: Eon with 50A and 5 Ohm Rg

Eon vs. Id, Rg=5 ohms, Cgs=0nF

50A Eon vs. Rg

Best regards,

Sean